SPI Review Edelman Ultrasound Physics

Pataasin ang iyong marka sa homework at exams ngayon gamit ang Quizwiz!

what does applying a wall filter do for color fill

wall filter eliminates low frequency doppler shifts , removing color from slow moving blood cells

the units for all intensities are

watts/cm2

what are the units for intensity?

watts/cm^2

what is the parameter determined by both the medium and sound source

wavelength

quality factor

a unitless number that is inversely related to bandwidth

decibels are a ____. the measured level is divided by the starting level

ratio

Sound waves produced by very small sources diverge in the shape of a _____.

V and are known as huygens' wavelets, spherical waves, or defraction patterns

ohm's law equation

Voltage (V) = Current (I) x Resistance (R)

All intensities have units of?

W/cm2

How is clutter or ghosting artifact eliminated?

Wall filter ( they serve as reject for doppler )

what are the units for power?

Watts or J/s

what are the units for acoustic impedance

rayls Impedance is often represented by the letter Z

what are the two kinds of magnification

read & write zoom

Impedance is important in ____ at boundaries.

reflections

focal zone

region around the focus where the beam is relatively narrow

Near Zone (or Near Field, or Fresnel Zone)

region from the transducer to the focus ( for CW, the diameter of the sound beam as it leaves the transducer is the same diameter of the active element. at the end of the near zone, the beam narrows to only 1/2 the width of the active element )

transducer frequencies of 2 MHz to 10 MHz are used to perform clinical doppler exams. however, doppler shifts range from

20Hz to 20,000Hz ( the range of audible sound)

calculating the number of gray shades

2^number of bits (ex. 2 bits = 2^2=4

what is the log of 1,000

3 ( 10*3)

typical values for propagation speed are

500m/s-4000m/s (depending on tissues it is traveling through)

what are the typical values for amplification

60-100 dB

for color to appear in a vessel, an angle other than _____ must be created

90 degrees

Where is lateral resolution the best?

@ focus. focus where the beam is narrowest

Enhancement artifact

Appears as a hyperechoic region beneath tissues with abnormally low attenuation. they are the opposite of shadowing. can be clinically useful. it may provide valuable diagnostic information that helps to characterize tissue. it is entirely unrelated to the speed at which sound travels in a medium

where is the pressure lowest at location A B C through a stenosis

B baby - kinetic energy increases with the higher velocity through the narrowing. as kinetic increases, pressure decreases ( it converts into kinetic as the blood accelerates)

Negative decibels

Describe signals that are DECREASING in strength or GETTING SMALLER ( when the intensity is reduced to 1/2 its original value, the relative change is -3dB) ( when the intensity is reduced to 1/10 its original value, the relative change is -10dB)

what is depth of view

Describes the maximum distance into the body that an ultrasound system is imaging

beneficence

Doing good or causing good to be done; kindly action

how does frequency affect focal depth?

Frequency and focal depth are directly related.

contrast agents

Gas bubbles encapsulated in a shell

Is amplitude adjustable?

Initial amplitude is, yes.

Is power adjustable?

Initial power is adjustable yes via the U/S machine.

what is the relationship between the prp and prf

Inversely related and reciprocals ( the longer the prp --> lower prf) PRF= 1/PRP

Temporal resolution artifact

Low frame rates. Less accurate positioning of reflectors in motion. -the ability to precisely position a moving structure

linear phased arrays crystals amount, shape, & width

amount: 100-300 shape: rectangular and narrow width: 1/4 to 1/2 of sound's wavelength

the y axis for a mode displays

amplitude

clutter

another form of noise. it is the presence of false echo signals arising from location outside of the main sound beam

what is power modulation harmonic imaging

another imaging technique specifically designed to augment harmonic reflections, which contain less distortion

pulsed wave doppler

Only PZT crystal is necessary. The crystal alternates between sending and receiving US pulses.

What are the 3 bigness parameters? (CW)

P.I.A power amplitude intensity

what is the decreasing order of impedance of a transducer

PZT > matching layer > gel > skin

adjustable focus systems are called

Phased array

What are the 3 acoustic variables?

Pressure (P), density (ρ), and distance (particle vibration)

spatial resolution artifact

Related to the overall detail in an image. determined by line density, axial resolution, and lateral resolution

Snell's Law Equation

Sin (transmission angle)/Sin (incident angle) = Speed of Medium 2/ Speed of Medium 1

what is pulse repetition period determined by?

Sound source only & imaging depth that the sonographers select

What is duty factor determined by?

sound source

what is pulse repetition frequency determined by?

sound source.. it is determined by the max imaging depth of the system

I sapa

spatial average, pulse average

_____ is the distance that a pulse occupies in space from the start to the end of a pulse

spatial pulse length

__ improves with high pixel density and creates an image with greater detail

spatial resolution

the __ or image detail of an analog scan converter is excellent because of the large number of storage elements within the matrix

spatial resolution

horizontal lines in a display

spatial resolution is affected by the number of horizontal scan lines per frame. spatial resolution is best with a greater number of lines

_ describes the relative relative weight of a material.

density. when equal volumes of two materials are compared, the dense material weighs a lot, whereas the non dense weighs little

the loss of piezoelectric properties is called

depolarization

the x-axis for a mode display represents

depth

Accuracy of reflector depth positioning in A mode, M mode, B mode and 2D imaging is called

depth calibration

characteristic of speed error

- correct number of reflectors - improper depth - appears as a step off

what is the difference spatial pulse length and pulse duration

spl = the distance while pd = the time

what are characteristics of enhancement

- hypoechoic (appears the same as the foreground color) - the result of too little attenuation - located beneath a structure with abnormally low attenuation

deep focus and focal depth

- larger diameter PZT - higher frequency

the numerical value of the mechanical index, and therefore, harmonic production, increases with

- lower frequency sound and - stronger sound waves ( substantial pressure variation)

what are two characteristics that create pulses of long duration?

- many cycles in the pulse or - individual cycles with long periods

refraction occurs only if two conditions are satisfied:

- oblique incidence ( not normal) and - different propagation speeds of the two media

under what conditions will the transmission angle equal the incident angle

- oblique incident - different propagation speeds ( speed 1 = speed 2)

receiver corrects for attenuation with a process called

compensation

what are the 5 parameters determined by just the sound source?

- period - frequency - amplitude - power - intensity

what is period determined by?

determined by the sound source only, not the medium

beam former

determines the firing delay patterns for phased array systems

determinants of sound beams for the characteristic: beam divergence

diameter of ceramic and frequency of sound

determinants of sound beams for the characteristic: focal length

diameter of ceramic and frequency of sound

__ presents processed data.

display

what is the relationship between the velocity of blood and doppler shift?

doppler shift is directly related to the velocity of the blood cells

maximum sensitivity

evaluated with the output power and amplification of the system set to the maximum practical levels

right angle

exactly 90 degrees

when exposed to the low pressure component of a sound beam ( rarefaction), contrast microbubbles ____

expand to a greater extent than they shrink

the most important operational parameter associated with an ultrasound movie is the systems ability to create numerous frames each second. this parameter is called

frame rate

what is temporal resolution determined by?

frame rate

_____ is the number of particular events that occur in a specific duration of time. in ultrasound, this of a wave is described as the number of cycles that occurs in one second

frequency

the elapsed time from pulse create to pulse reception is called

go return time or time of flight

B-mode was the first form of

gray scale imaging, which is the basis for all other types of gray scale imaging, including real time imaging

Attenuation in air is _______ attenuation in soft tissue.

greater than

Attenuation in bone is _________ attenuation in soft tissue.

greater than

-3dB means

half

when the signal to noise ratio is ___, the signal is much stronger than the noise and the image is of high quality

high

advantage of continuous wave doppler

high sensitivity; there is no aliasing; able to measure very high velocities

an ultrasound machine is imaging to a depth of 2 cm. would the PRF be described as high or low

high when imaging shallow depth... shorter time to create new pulse therefor prf can be higher

A sound wave, with an intensity of 50 W/cm², strikes a boundary and is totally reflected. What is the: intensity reflection coefficient? reflected intensity?

intensity reflected coef = 100% ( all reflected) reflected insentiy = 50 w/cm2

two methods of focusing for mechanical transducers are

internal focusing with the use of a curved active element external focusing with the use of an acoustic lens

what is the relationship between frequency and period

inversely related (p * f = 1) --> reciprocal

reflected intensity

is the intensity of the portion of the incident sound beam that, AFTER striking a boundary, RETURNS BACK from where it came.

quality assurance

is the routine, periodic evaluation of an ultrasound system to guarantee optimal image quality. these must be performed periodically and routinely

what does the acoustic insulator do for a transducer

isolates the internal components of the transducer from the case. prevents vibrations in the case from inducing an electrical voltage in the PZT of the transducer

acute angle

less than 90 degrees

wide dynamic range means

many shades of gray ( low contrast image )

___ maintains and organizes the proper timing and interaction of the system's components

master synchronizer

Sound travels fastest in

materials that are stiff but not dense (aka bone)

what is the prefix, symbol and value for an exponent of 10^-6

micro, u, 1/1000000

what is the prefix, symbol, and value for an exponent of 10^-3

milli, m, 1/1000

what are the units for spatial pulse length?

millimeters (mm)

what are the units for pulse repetition period?

milliseconds

what is harmonic imaging

the creation of an image from sound reflections at twice the frequency of the transmitted sound

focal length or near zone length

the distance from the center of a lens to the focal point

half-value layer thickness

the distance sound travels in a tissue that reduces the intensity of sound to one-half its original value ( the HVL may also be described as the depth of tissue that results in 3 dB of attenuation to the intensity) (aka... penetration depth, depth of penetration, half boundary layer)

Acoustic propagation properties are?

the effects of the medium upon the sound wave

phase delay

the electrical signals are separated by then billionth of a second. these differences between the wavelets create a single beam. the time delays are the phase delays

bioethics

the ethics of medical and biological research

analog scan converter

the first type of scan converter and made gray scale imaging possible

viscosity describes

thickness of a fluid

Can amplification alone make an image of uniform brightness from top to bottom?

no

what is the value for an exponent of 10^0

1

can output power along make an image uniform brightness from top to bottom?

no

will a vessel ever be filled with color if it is perpendicular to sound

no

what is the parameter that is determined by the medium only

speed

units for flow

volume divided by time L/min 5L/min

the frequency of a transducer does not change. if the diameter of the new pzt crystal increases, what happens to the wavelength

no change

a disadvantage of selecting a lower frequency transducer for reducing aliasing

no significant disadvantage except forr lower frequency sound produces lower quality anatomic image

focus or focal point

~the location where the beam reaches its narrowest --> minimum diameter.

what is the effect of demodulation on an image

none. the purpose of it is to change the form of the electrical signal so that it is appropriate for the display

a disadvantage of selecting a new view with shallower sample volume for reducing aliasing

none. the sonograpehr wants a location that is shallower

harmonic frequency sound arises from

nonlinear behavior

non linear behavior

nonlinear means irregular or disproportionate. a system is nonlinear when it behaves unevenly

the very top of the doppler display is called the _____, whereas the bottom is called ____

nyquist limit, alaising

objective vs subjective standards

objective is completely unbiased, while subjective is influenced by experiences or beliefs

What is a PACS system?

( Picture Archiving and Communications System) A computer system that not only allows acquisition, but also the interpretation, storage and recall of each medical image in digital form.

what is the meaning of 20 dB

(10dB means 10 times bigger 20 dB is 10dB and 10dB therefore 20 dB means 10 x 10 or ) 100 times bigger

what is the meaning of a 6 dB change?

(3dB means 2 times bigger 6 dB is 3dB and 3dB therefore 6dB means 2 x 2, or) 4 times bigger

characteristics of lobe artifact

-a second copy of the true reflector -the artifact and the true reflector are located side by side at the same depth

Doppler packet disadvantages:

-more time needed to acquire data - reduced frame rate -decreased temporal resolution

hydrostatic pressure of a supine patient

~zero at all locations

6 assumptions of imaging systems

-sound travels in a straight line, -sound travels directly to a reflector and back, -sound travels in soft tissue at exactly 1540 m/s, -reflections arise only from structures positioned in the beam's main axis, -the imaging plane is very thin, -the strength of a reflection is related to the characteristics of the tissue creating the reflection.

what are the typical values for power?

.004-.09 watts ( 4-90 milliwatts)

what is the typical value of a period?

.06-.5 us (microseconds)

what are the typical values for axial resolution

.1 to 1 mm ( lower numbers indicate shorter pulses and improved image accuracy)

what are the typical values for wavelength?

.1-.8mm

what are the typical values for spatial pulse length ?

.1-1.0 mm ( length in soft tissue)

what are the typical values for half value layer thickness

.25-1.0 cm

Cosine of angles: 0 degrees = __ cosine 30 degrees = 60 degrees = 90 degrees = 120 degrees = 150 degrees = 180 degrees =

0 degrees = 1 30 degrees = .87 60 degrees = .5 90 degrees = 0 120 degrees = -.5 150 degrees = -.87 180 degrees =-1

decimal numbers

0-9

what are the typical values for duty factor?

0.2% to 0.5% (DF is 100% for CW)

what are the typical values for pulse duration?

0.3 μs to 2.0 μs.

example of binary number

0101010011

five techniques may be used to avoid aliasing artifact:

1) adjust the scale to its max ( prf to the max) 2) select a new view with a shallower sample volume 3) select a lower frequency transducer 4) use baseline shift 5) use CW doppler

what are the three basic modes of display, or formats, of viewing ultrasound information have significance

1. amplitude mode 2. brightness mode 3. motion mode

what are the consequences of using backing materials

1. decreased sensitivity 2. wide bandwidth 3. low quality factor

translating image information from the real world ( analog) to the computer world (digital) and back again is a five step process which includes:

1. electrical signals created by the transducer during reception are converted from analog to digital form by the analog to digital converter ( the digital information is a string containing only 0s and 1s) 2. the digital information is stored in the scan converters computer memory. any processing of the reflected signals before storage is called preprocessing. 3.the image information (still digital form) continues to be processed by the ultrasound systems computer. any processing after storage in the digital scan converter is called 4. digital signals cannot be directly displayed on analog display devices. digital signal must be translated back into analog from by digital to analog converter 5. the signal, now in analog form is presented on the analog video display for interpretation

Attenuation is determined by

1. path length ( the farther the sound travels, the greater attenuation and weaker the beam.. distance and attenuation are directly related) 2. frequency of sound ( attenuation is greater in higher frequency sound than lower.. frequency and attenuation are directly related)

what four distinct modifications happen when a beam is focused

1. the beam diameter in the near field and the focal zone narrows 2. the focus is moved closer to the transducer ( near zone is reduced 3. beam diameter beyond the focal zone widens. so focusing improves lateral res in the near and focal zones, and degrades lateral resolution beyond focal zone 4. size of focal zone is reduced. ( narrowest = where lat res is best)

an ultrasound system is highly sophisticated. it creates sound pulses, retrieves reflections, and presents audio and visual information for our interpretation. the system has two major functions:

1. the preparation and transmission of electrical signals to the transducer, which creates a sound beam 2. the reception of electrical signals from the transducer, with subsequent processing into clinically meaningful images and sounds

what is the wavelength of a 1 MHz sound in soft tissue?

1.54mm

what is the wavelength of other frequency sound waves in soft tissue ( use 2 MHz)

1.54mm/2 = .77mm

what are the five order of receiver operations for the system to function properly?

1.amplification 2. compensation 3. compression 4. demodulation 5. reject ( order is alphabetical)

what are the typical values for pulse repetition period?

100 us - 1 ms ( prf is generally 100 to 1000 times longer than pulse duration)

Sound is traveling in a medium and strikes a boundary with normal incidence. If 63% of the wave's intensity is reflected back toward the transducer, what percentage is transmitted?

37% intensity will be transmitted. conservation of energy occurs at the boundary. 63+37=100%

what is the log of 10,000

4 ( 10*4)

bit

A contraction of "Binary Digit". A bit is the single unit of information in a computer, typically represented as a 0 or 1. smallest amount of computer memory

reverberations resemble

A ladder or Venetian blind

revocation of consent

A patient may withdraw previously granted consent at any time

characteristics of refraction artifact

A second copy of the reflector. The copy is side by side, or at the same depth as the true reflector.

attenuation coefficient in soft tissue

AC and freq directly related. the AC is 1/2 the freq. AC(dB/cm) = freq (MHz) / 2 0.5 dB/cm/MHz

gray shades on a doppler spectrum are related to

Amplitude of reflected signal or number of blood cells creating reflection

risk benefit relationship

Benefits to the patient must outweigh the risks of the exam

How are amplitude and power related?

Both describe size or magnitude of a wave. Directly related. When one increases, so does the other. ( power is proportional to the amplitude squared)

what is spatial pulse length determined by?

Both the source and the medium ( it equals the number of cycles in each pulse times the wavelength of each cycle)

what is wavelength determined by?

Both the source and the medium ( it is the only parameter that is determined by both the source and the medium)

digital scan converter

Computer memory that stores echo information a process called digitizing

How does the sonographer change duty factor?

Changes when imaging depth is altered. as depth increases, transmit time remains constant while listening time is prolonged. The duty factor decreases. Duty factor increases when systems image superficially.

comet tail artifact is created when

Closely spaced reverberations merge

a word of computer memory

Consists of 2 bytes or 16 bits

range ambiguity artifact

Created by a reflector that is located deeper than the maximum displayed depth

axial resolution artifact

Created when a long pulse strikes two closely spaced structures, where one is in front of the other, or parallel to the main axis of the beam. Only one reflection will appear on the image if the structures are closer together than one-half the spatial pulse length.

the 13 microsecond rule

For every 13 MICROSECONDS of GO-RETURN TIME, the object creating the reflection is 1 CM DEEPER in SOFT TISSUE

what are the units for frequency?

Hertz (Hz) 1 cycle/second = 1Hz

characteristics of edge shadowing

Hypo- or anechoic (background color) Results when the beam spreads after striking a curved reflector Extends downward from the curved reflector's edge, parallel to the beam Prevents visualization of true anatomy on the scan

what are the units for pulse repetition frequency

Hz, or per second

Temporal intensities from largest to smallest

I tp, I max, I pa, I ta

imaging vs doppler

IMAGING DOPPLER 1. Normal incidence-90 degrees 2. High Freq-improves resolution 3. Pulsed wave only 4. Minimum of 1 PZT 4. 1pzt-PW or 2pzt-CW DOPPLER 1. 0 or 180 degrees (true velocity) 2. lower freq- avoids aliasing 3. PW or CW 4. 1pzt-PW or 2pzt-CW

wide bandwidth or broadband

Imaging probes produce pulses that are identified as these.

what are other names for axial resolution

LARRD Longitudinal, axial, range, radial or depth resolution

mnemonic for lateral resolution is

LATA lateral, angular, transverse, azimuthal

what is a channel

Made up of a single PZT element, the electronics in the beam former/pulser, and the wire that connects them

Piezoelectric Materials

Materials which CONVERT SOUND into ELECTRICITY and vice versa

dosimetry

Measure of radiation dose to an individual

I sppa

Measured at 1. the LOCATION where intensity is MAXIMUM (spatial peak) and 2. AVERAGED over the TRANSMIT TIME (pulse average) (spatial peak, pulse average)

I spta

Measured at 1. the LOCATION where intensity is MAXIMUM (spatial peak) and 2. AVERAGED over ALL TIME (both TRANSMIT and RECEIVE) ( spatial peak, temporal average)

I sptp

Measured at 1.the LOCATION where intensity is MAXIMUM (spatial peak) and 2. the instant in TIME that the MOST POWERFUL part of the pulse passes (temporal peak) ( spatial peak, temporal peak)

I sata

Measured over 1. the ENTIRE cross-sectional area of the sound beam (spatial average) and 2. over ALL TIME (temporal average) ( spatial average, temporal average)

what is propagation speed determined by?

Medium only - density and stiffness

Is propagation speed adjustable?

No *Speed changes only when the wave travels from one medium to a different medium.

Is wavelength adjustable?

No, wavelength cannot be changed by the sonographer when using a particular transducer.

Can sound travel through a vacuum?

No. Sound must travel through matter and there is no matter in vacuums.

is pulse duration adjustable?

No. The sonographer cannot alter pulse duration while using a particular ultrasound system and transducer.

what are the units for duty factor?

None. Percentages do not have units.

range error artifact

Propagation speed errors are also called

refraction

The bending of a wave as it passes at an angle from one medium to another ( refraction is transmission with a bend)

radiation force

The force exerted by a sound beam on an absorber or a reflector AKA feedback microbalance

transmitted intensity

The intensity of the portion of the incident sound beam that AFTER striking the boundary, CONTINUED FORWARD in the direction it was traveling

Intensity Transmission Coefficient (ITC)

The percentage (%) of the intensity that passes in the FORWARD DIRECTION when the sound beam strikes the interface between 2 media

Respiration affects venous flow for 2 reasons:

The venous system is low pressure Muscles responsible for respiration alter pressures in the thorax and the abdomen

what are the units for pulse duration?

Units of time like microsecond (μs).

Compensation creates an image that is

Uniformly bright from top to bottom

curved and oblique reflectors

When a sound beam strikes a curved or oblique reflector, some of the reflected sound may be directed away from the transducer.

REFLECTION ANGLE = INCIDENT ANGLE

When reflection occurs with oblique incidence, the sound beam is NOT redirected back to the transducer, but rather in a DIFFERENT DIRECTION. The direction it goes in will be EQUAL and OPPOSITE to the incident angle: ANGLE OF INCIDENCE = ANGLE OF REFLECTION

the reynolds number predicts

Whether flow is laminar or turbulent

b-modes x and z axis

X: depth (derived from the time of flight information of the sound pulse Z: amplitude

the x and y axis for m mode

X: time y: depth

Is intensity adjustable by the sonographer?

Yes, initial intensity, like power and amplitude, can be adjusted by the sonographer.

Is the pulse repetition period adjustable?

Yes. Adjust depth.

Is the duty factor adjustable?

Yes. Changing the depth of view of a scan also changes the duty factor.

what is he equation for impedance

Z (rayls) = density (kg/m^3) x prop. speed (m/s)

what is gravitational energy

a form of stored or potential energy. is associated with any elevated object

a byte is

a group of eight bits of computer memory, such as 10011111

B-mode appears as?

a line of dots of varying brightness

turbulent flow converts flow energy into other forms such as sound and vibration. sound associated with turbulence is called

a murmur or a bruit

a stenosis is __

a narrowing in the lumen of a vessle

M mode is the only one that provides information about a reflector's changing location with respect to ______________.

a or b mode

what are considered out-of-phase waves?

a pair of waves that have their peaks at different points and at different times

what are considered in-phase waves?

a pair of waves that have their peaks at the same time and same location

lateral resolution

ability to distinctly identify two structures that are very close together when they are side by side or perpendicular to the sound beams main axis

___ occurs when ultrasonic energy is converted into another form of energy

absorption . like scattering, absorption is directly related to frequency. as a result of absorption, higher freq waves attenuate more than lower frequency waves. sound traveling in bone undergoes extensive absorption

name the three components of attenuation

absorption, reflection, scattering

sound waves are also known as ____ waves

acoustic

Phased array always means:

adjustable or multi-focus

what is acoustic impedance determined by

associated with the medium only. it is calculated, no measured

when sound waves weaken as they propagate, they decrease in intensity, power, and amplitude as sound travels.. this is known as

attenuation

10 bB of attenuation means

attenuation means weakening so the dB is -10dB

As a sound beam strikes a boundary energy is ______ and what equation applies?

conserved and 100% of the intensity must be accounted for 100% = inten. reflection coef. (IRC)(%) = intensity trans. coef. (ITC) (%)

acousto-optics

based on the interaction of sound and light a shadowing systme caled a schlieren allows us to view the shape of sound beam in a medium

With phased, linear, annular and convex array probes, the ___________ coordinates the electrical signals sent to each active element.

beam former

a disadvantage of using baseline shift to reduce aliasing

can be ineffective if aliasing wraps

turbulence is often associated with ____ and elevated blood velocities

cardiovascular pathology

what is the prefix, symbol, and value for an exponent of 10^-2

centi, c, 1/100

effects of a stenosis

change in flow direction increased velocity as vessel narrows turbulence downstream from the stenosis pressure gradient across the stenosis loss of pulsatility

what kind of interference occurs with in-phase waves?

constructive interference

When pulsed and continuous wave sound beams have the same SPTP intensities, which wave has the higher SPTA intensity

continuous

when pulsed and continuous wave beams have the same SATP intensities, the ____ wace beam has the higher SATA intensity

continuous

units for compression

dB

what are the units for amplification

dB

what are the units for compensation?

dB

what are the units for attenuation coefficient

dB/cm

With edge shadow, the sound beam refracts at the edge of a curved reflector. the beam spontaneously diverges, resulting in a drop in intensity. this causes

edge shadowin

what does the wire do for a transducer

electrical connecting between the pzt and ultrasound system. where the voltage returns to the system

linear phased array transducers sound beam's are focused

electronically

An array comprises a single slab of PZT cut into a collection of separate pieces called _______.

elements

what happens if a crystal is damaged for linear phased array tranducers

inconsistent or erratic beam steering and focusing

lateral resolution artifact

occurs when a pair of side-by-side reflectors are closer than the width of the sound beam -Two objects appear as one reflection on the image - may display a small reflector as a wide line rather than a narrow dot AKA point spread artifact

oblique incidence

occurs when the incident sound beam strikes the boundary at any angle other than 90 degrees ( not at right angles or perpendicular)

electrical resistance is reported in units of

ohms

_____ describe the features of a sound wave

parameters

respect for autonomy

patient has capacity to act intentionally, with understanding and with free will. informed consent

conservation of energy

percent of sound reflected and transmitted must equal 100

3 rules for powers of 10s

positive exponents are >10 negative exponents are <10 0 exponent has a value between 1 and 10

____ is the manipulation of image data after storage in the scan converter

postprocessing

___ is the rate of energy transfer or the rate at which work is performed.

power

___ is the manipulation of image data before storage in the scan converter

preprocessing

fast fourier transform is used to

process both pulsed and CW doppler signals

informed consent

process where the patients are educated about the essentials of a medical procedure

what of ultrasound is the random redirection of sound in many directions

scattering (sound scatters when the tissue interface is small ( equal to or less than the wavelength of the incident sound beam) ) ( lung tissue scatters sound because the alveoli are filled with air )

advantage of pulsed doppler

selecting exact location of the doppler interrogation, called range resolution range specificity freedom from range ambiguity artifact

normal sensitivity

settings are those at which all the pins, solid masses, and cystic structures in the test phantom are accurately displayed

images displayed one frame at a time in a process called

static scanning

______ occurs when a fluid moves at a constant speed or velocity. ( present in venous circulation when pt stops breathing for a second)

steady flow

__ describes the ability of an object to resist compression

stiffness (will retain it's shape)

proper methods for quality assurance programs are

test under known, defined conditions use constant instrument settings use a phantom with measurable characteristics image in an identical environment

the disadvantage of diffuse reflection is

that backscattered signals have lower strength than specular reflections

an advantage of diffuse reflection is

that interfaces at suboptimal angles to the sound beam can still produce reflections that will return to the transducer

spatial peak intensity ( Isp) is

the maximum in space

peak intensity is

the maximum value

what is the relationship between actual velocity and measured velocity when blood moves at a 60 degree angle to the beam?

the measured velo at 60 degrees is one half of the actual velocity ( since cosine of 60 is .5)

the half value layer thickness depends on

the medium and the frequency of sound

pixel density

the number of picture elements per inch

incident intensity

the sound wave's intensity immediately before it strikes a boundary

what is the significance of displaying all component frequencies with fast fourier transforms

the spectral display of FFT distinguishes laminar from turbulent flow

Hemodynamics defined

the study of blood moving through the circulatory system

compensation operation or uniformity

the systems ability to display similar reflectors in the phantom with echoes of equal brightness

the vessel is tilted so the top right is high and the bottom left is low, which way do you steer your color box

to the right

____ indicated the speed of swiftness of a fluid moving from one location to another. (how fast)

velocity

____ is defined by a magnitude and a direction.

velocity

Bernoulli's Principle describes the relationship between

velocity and pressure in a moving fluid

resonant frequency

vibrates freely for a long time at a single frequency

What appears on an image when two reflectors positioned perpendicular to the sound beam are closer to each other than the beam width?

when 2 close reflectors other than the width of the beam, only one reflection is observed in the image

positive doppler shifts

when blood cells move towards the transducer. this results in reflected frequency higher than transmitted

when is temporal resolution reduced?

when few images are displayed per second (low frame rate)

what happens if the crystal is damaged for mechanical transducers

whole image is lost

Is amplification adjustable?

yes

does increasing the scale have any other effect on a color doppler image

yes, increasing the scale decreases the sensitivity to slow flows

is there another form of nonlinear behavior of a microbubble that creates contrast harmonic?

yes, it occurs with contrast agents. which is a non linear relationship betweeen mechanical index and harmonic creation

does the sonographer control postprocessing?

yes, which all postprocessing changes can be reversed, which will restore the initial numerical values of the image data

does the sonographer control preprocessing?

yes, which it alters the image data forever and cannot be reversed or undone

is compensation adjustable?

yes. TGC's

Is reject adjustable?

yes. it usually has two levels: one that is built in and one that is adjustable

is output power adjustable

yuh

an advantage of using baseline shift to reduce aliasing

zero baseline shift allows the high velocity flows to be displayed in the proper direction, which allows measurements of max velo to remain accurate even after changing baseline

what is DICOM

(Digital Imaging and Communications in Medicine) a set of rules, or protocols, that allows imaging systems to share info on a network

how does speed of sound in pzt affect frequency

(in PW transducer) the speed of sound in PZT and the frequency of sound are directly related.

characteristics of focal enhancements

- a hyperechoic side to side region ( appears the same as the foregound) - results from increased intensity at the focus

a-mode displays are created as

- a sound pulse is emitted by the transducer, a dot moves at a constant speed across the system's display - when a reflection returns to the transducer, it is processes and the moving dot is deflected upward on the screen

pulse duration's relationship to - number of cycles in the pulse - period - frequency

- directly related to # cycles - directly related to period - inversely related to freq (MHz)

spatial pulse length's relationship to - # cycles in the pulse - wavelength - frequency

- directly to the # cycles - directly to the wavelength - inversely SPL (mm)= # cycles * wavelength (mm)

what are two characteristics that create pulses of short duration ?

- few cycles in the pulse or - individual cycles with short periods

what are two characteristics that create short pulse length

- fewer cycles in the pulse - cycles with shorter wavelengths

five goals of a quality assurance program are

- guarantee proper operation of the system - select gradual changes - minimize downtime - reduce the number of non diagnostic exams - reduce the number of repeat scans

advantages of power mode

- increased sensitivity to low flow or velocity, such as venous flow or flow in small vessels - anaffected by doppler angles ( unless the angle is 90 degrees) - no aliasing, since the velocity information is ignored

Color doppler provides information on the location of flow and therefore

- is a pulsed ultrasound technique - has range resolution ( or range specificity ) - is subject to aliasing

factors the affect beam divergence in the far field for less divergence

- larger diameter - higher frequency

Shallow imaging ( duty factors)

- less listening - shorter prp - higher prf - higher df

Doppler packet advantages:

- more accurate velocity measurement - increased sensitivity to flow

deep imaging (duty factors)

- more listening - longer prp - lower prf - lower df

three disadvantages of power mode

- no measurement of velocity or direction - lower frame rates ( reduced temporal resolution) - susceptible to motion of the transducer, patient, or soft tissues, which may result in a burst of color, or flash artifact

two forms of sensitivity are

- normal - maximum

tissue harmonics are: ( summary)

- not present as sound leaves the transducer; they are created deeper in the tissues - created in the tissues during transmission - created by nonlinear behavior int he speed of sound. sound in compressions travels faster than in rarefactions - primarily created along the beams main axis

Artifacts include reflections that are described as:

- not real - not seen on the image - incorrect shape or size - incorrect position - incorrect brightness

what factors affect the number of pulses needed to create an image?

- number of pulses per scan line ( number of focal points) - sector size - line density( lines per angle of sector)

whaat conditions create aliasing

- occurs only with pulsed doppler, never with CW - occurs when the doppler sampling rate is too low in comparison to the measured blood velocities

what two forms are there for laminar flow

- plug flow - parabolic flow

What should the sonographer do when first meeting a patient?

- respectfully introduce yourself - identify the patient

Multi-focus & temporal resolution

- single focus = 1 sound pulse is transmitted. - multi focus = increase in pulses transmitted.

factors that affect beam divergence in far field for more divergence

- smaller diameter - lower frequency

shallow focus and focal depth

- smaller diameter PZT - lower frequency

when the mediums speed is faster than that in soft tissue ( speed error)

- sound travels faster than the ultrasound system expects - pulses return from their trip in the body (fast) - go return time is too short - system assumes reflectors are close to the transducer -reflectors are located too shallow on image -distances are underestimated

when the medium's speed is slower than that in soft tissue ( speed error)

- sound travels slower than the ultrasound system expects - pulses return from their trip in the body ( slowly) - go return time is too long - system assumes reflectors are far from the transducer - reflectors placed too deep on image - distances are overestimated (reported number is too large)

Tissue equivalent phantoms are similar to soft tissue in the following ways

- speed of sound (1540m/s) - attenuation - scattering characteristics - echogenicity

with a pulsed wave transducer, two characteristics of the active element combine to determine the frequency of sound:

- speed of sound in the pzt - thickness of the pzt

what are things to consider when obtaining color fill in the vessel

- steering - gain - angle of incidence should not be 90 - aliasing

in differences appear between the ultrasound scan and the actual pin locations in the test object, the error may be caused by

- system malfunction - the speed of sound in the phantom is different than 1540 ms

what are the advantages of beam formers?

- system modifications and updates often require only software programming (making it more flexible) - digital systems are extremely stable ( wont fall out of calibration) - digital systems are versatile ( can use transducers with many frequencies)

what is the significance of the gradual development of a harmonic signal ?: during fundamental imaging, significant amounts of artificat arise within the first few centimeters of a tissue. these strong artifacts appear for 2 reasons

- the beam is very strong - the many different superficial anatomic layers distort the sound beam

How is M mode displayed?

- the reflections move at a constant speed from right to left across the screen - squiggly lines represent changing depth of the reflecting surfaces

characteristics of low freq pulsed wave imaging transducers

- thicker pzt crystals - pzt with lower speeds

characteristics of high frequency pulsed wave imaging transducers

- thinner pzt crystals - pzt with higher speeds

devices to ensure quality assurance

- tissue equivalent - doppler phantom - beam profile/ slice thickness phantom

what are the two components of pulse repetition period? which one can the sonographer change

- transmit time (pulse duration--> sonographer cannot change) - receive time

doppler phatom

- vibrating string - moving belt - flow phantom

attenuation of ultrasound in media - water - blood, urine, etc - fat - soft tissue - muscle - bone and lung - air

- water -- extremely low - blood, urine, etc--low - fat--low - soft tissue --intermediate - muscle --higher - bone and lung -- even higher - air -- extremely high

pulse repetition frequency and max imaging depth

- when the depth of view is shallow, prf is high & vice vera (PRF is inversely related to the max imaging depth)

A sound beam has decreased to 1/100 of its initial intensity. How is this described in decibel notation?

-20dB (1/10 x 1/10 = 1/100... 1/10 in dB notation is -10dB.. double that to make 1/100.. -20dB)

characteristics of mirror image

-A second copy of a true reflector -The copy appears deeper than the true reflector -A bright reflector, the mirror, lies on a straight line between the artifact and the transducer. -True reflector and artifact are equal distances from the transducer

Is period adjustable?

-No. The sonographer cannot change the period while using a basic ultrasound system with a particular transducer.

what are the two components of pulsed ultrasound?

-Transmit, talking, or on time -Receive, listening, or off time

tissue harmonics

-created during transmission in tissue -occurs as sound propagates in tissue -results from nonlinear behavior of transmitted sound beam -weaker harmonic signal

doppler shift measured in hertz

-directly related to velocity -directly related to transducer frequency

coded excitation provides

-higher signal-to-noise ratio -improved axial resolution -improved spatial resolution -improved contrast resolution -deeper penetration

disadvantage to continuous wave doppler

-the exact location of the moving blood cells cannot be determined. (range ambiguity) - lack of time gain compensation ( reflections created form deeper blood cells will have a lower amplitude than reflections from blood cells at shallower depths---> doppler shifts produced by a deeper BC may be incorrectly interpreted as having been created by fewer blood cells)

artifacts result from

-violation of assumptions -equipment malfunctions or poor design -the physics of ultrasound -operator error

with a fixed focus transducer, two factors combine to determine the focal depth:

1) transducer diameter 2) frequency of the sound

What are the 7 acoustic parameters?

1. Period 2. Frequency 3. Amplitude 4. Power 5. Intensity 6. Wavelength 7. Propagation speed

three processes contribute to attenuation:

1. Reflection 2. Scattering 3. Absorption

acoustic impedance = _____ x ______

Impedance = density (kg/cm3 ) x propagation speed (m/s)

how does density affect speed?

Speed and density are inversely related. As materials become more dense, the speed of sound in the material decreases. Therefore, sound travels faster in media with low density.

How does stiffness affect speed?

Stiffness and speed are directly related. As materials become stiffer, the speed of sound in the material increases.

What is pulsed sound?

a pulse of ultrasound is a collection of cycles that travel together, a pulse must have a beginning and an end.

decibel notation is

a relative measurement, a comparison, a ratio, logarithmic

the ____ ____ is an important tissue property that influences the amount of reflection

acoustic impedance

an advantage to using continuous wave doppler for reducing aliasing

aliasing never appears on CW, bc aliasing is only related to PW

how does persistence and spatial compounding differ?

all of the image used in persistence are from the same view. the images used in spatial compounding are from different views or angles

temporal intensity refers to

all time, transmit and receive. a pulsed ultrasound beam does not have the same intensity at different times

the different measurements of intensities are important in the study of

bioeffects

bistable vs gray scale displays

bistable images are composed of only 2 displays : black and white gray scale have many levels of brightness with shades of gray

Negative Doppler shift

blood cells move away from the transducer. the reflected frequency is lower than the transmitted

velocity in a vessel decreases as

blood flows out of the stenosis into a vessel segment of normal diameter

why does blood move from one location to another?

blood moves from regions of high energy to low energy. ( energy gradient)

when the frequency of different waves differ, _____________ interference occur

both constrictive and destructive

Output power vs receiver gain

both control image brightness; patient expose to u/s energy is affected by alterations in output power, but not by changes in amplification - gain (when possible turn down power & turn up gain b/c power puts more into patient, gain doesn't put anything in) too dark, gain up. too bright, power down

how does transducer diameter affect beam divergence in the far field

crystal diameter and beam divergence are inversely related

isoechoic

describes structures with equal echo brightness

how do particles move in longitudinal waves?

in the same direction that the wave propagates. sound is a longitudinal wave.

A disadvantage of pulsed-wave Doppler (PW)

inaccurate measurement of high velocity signals because of aliasing

incident intensity formula

incident intensity = reflected intensity + transmitted intensity

fixed focusing

includes external and internal technique. the focal depth and the extent of focusing are determined when the transducer is fabricated and can't be fixed

advantage of adjusting scale to max to avoid aliasing

max prf raises the nyquist limit which allows for less alaising

Angles with a measure other than 90 degrees are _______?

oblique (includes acute & obtuse)

homogeneous

of the same kind; alike --- portion of the tissue or an image that has similar echo characteristics throughout

-10 dB means

one tenth

primary limitation of persistence

reduction in the displayed frame rate, which reduces temporal resolution

10 dB means...

ten times larger

Increase wall filter doppler output

the bottom one

__ is the distance or length of one complete cycle.

wavelength

the beam diameter at deeper than 2 near zone lengths is

wider than transducer diameter

what is lateral resolution determined by

width of the sound beam (narrower beams have better res)

Doppler packets

with color Doppler multiple pulses are used to accurately determine blood vessel velocities; these multiple pulses are called packets

in vitro

within a glass, observable within a test tube

in vivo

within the living body

Far Zone (Fraunhofer Zone)

~the region or zone deeper than the focus, beyond the near field. ( where the beam diverges or spreads out )

power doppler

(energy mode) non directional color doppler. amplitude mode of Doppler where it is not the shift itself that provides the signal but rather the strength (amplitude) of the shift

Focusing Techniques

(method name type) lens- external- fixed, conventional, or mechanical curved active element- internal- fixed, curved, or mechanical electronic- phased array- adjustable

Is spatial pulse length adjustable?

*No.* The sonographer cannot alter pulse length. In a particular medium, a transducer's pulse has a fixed length that cannot change.

Is the pulse repetition frequency adjustable?

*Yes*. The sonographer can change PRF by adjusting the depth of view of a scan.

A sound beam has increased from its initial intensity by a factor of 100. How is this described in decibel notation?

+20dB (10*10=100... 10 times in decibel notation is +10dB... therefore the dB notation for 100 is +10dB and another +10dB.. making +20 dB)

characteristics of shadowing

- Hypo or anechoic - Result of too much attenuation - Located beneath the structure with abnormally high attenuation - Prevents visualization of true anatomy on the scan

limitations of analog scan converters

- Image fades over time - Image flickering - Instability - Deterioration

what is intensity determined by

- Initially by the sound source -But changes as sound propagates through the body.

what is amplitude determined by?

- Initially the sound source -But it decrease as it propagates through the body ( rate of decrease depends on the medium)

advantages of digital scan converters

- Uniformity: consistent gray scale quality throughout the image - Stability: does not fade or drift - Durability: not affected by age or heavy use - Speed: nearly instant processing - Accuracy: error-free

characteristics of comet tail

- appears as a single long hyperechoic echo - located parallel to the sound beams main axis

curved and oblique reflectors: the amplitude of the reflection received by the transducer may be less than expected. in this case, reflectors :

- are absent on the image - appear too weak on the image or - appear different from other similar reflecting boundaries

four requirements for a quality assurance program are

- assessment of system components - repairs - preventative maintenance - record keeping

Devices measure the output of ultrasound transducers by absorption, or the conversion of sound energy into heat

- calorimeter - thermocouple - liquid crystal

what affects does a stenosis have on blood flow (possible)

- changes in direction ( as blood flows into and out of the narrow portion of the vessel) - increased velocity within the stenosis - post stenotic turbulence ( eddy flow) - pressure gradient across the stenosis ( the pressure downstream is lower than upstream bc loss of energy) - conversion of pulsatile flow patterns to steady flow

what two physical principles always apply to reflection with oblique incidence

- conservation of energy - reflection angle = incident angle

two user controls on video monitor can alter characteristics of displayed images

- contrast: determines the range of brilliance within the displayed image. bistable images are high contrast - brightness: determines the brilliance of the displayed image

operational settings for temporal resolution worse - lower frame rates

- deeper imaging - multiple focal points (improves lat res) - wide sector - high line density ( improves spatial res)

crosstralk results from either

- doppler gain set to high - an incident angle near 90 degrees between the sound beam and the flow direction

Venous flow in legs correlates with movement of diaphragm

- downward movement of the diaphragm (inspiration) decreases venous flow in the legs ( downward --> decreases) - upward movement of the diaphragm ( expiration) increases venous flow in the legs ( upwards --> increase) changes in venous return to the heart are opposite to the return from the legs

fast fourier transform has two advantages

- exceedingly accurate - displays all individual velocity components that make up the complex reflected signal

two methods of spectral analysis are currently used

- fast fourier transform (FFT) - autocorrelation

what are the three forms of energy associated with blood

- kinetic - pressure - gravitational ( the total energy at a specific location within the circulation is the sum of all three energy forms)

imaging depth and temporal resolution for deep imaging

- long go return time - longer Tframe - lower frame rate -inferior temporal resolution

characteristics of pulsed doppler

- low quality factor - lower sensitivity - wide bandwidth pulses

what are two characteristics that create long pulses

- many cycles in the pulse - cycles with longer wavelengths

what are the five additional parameters that describe pulsed sound?

- pulse duration - spatial pulse length - pulse repetition period - pulse repetition frequency - duty factor

two ways to avoid aliasing are

- raise the nyquist limit - reduce the doppler shift

four commonly accepted principles of health care ethics include

- respect for autonomy - nonmaleficence - beneficence - justice

operational settings for temporal resolution better - high frame rates

- shallower imaging - single focus - narrow sector - low line density

imaging depth and temporal resolution for shallow imaging

- short go return time - shorter Tframe - higher frame rate - superior temporal resolution

Improved axial resolution is associated with

- shorter spl - shorter pulse duration - higher freq ( shorter wavelength) - fewer cycles per pulse ( less ringing) - lower numerical values

Write magnification is characterized by

- the image used to identify the roi is discarded and all new image info is acquired - the number of pixels or scan lines in the roi image is greater than that in the rois portion of the original image - the increased number of pixels in the region of interest improves the spatial resolution

read zoom is characterized by

- the number of pixels or scan lines in the magnified image is the same as the original image - spatial resolution does not change because the number of pixels in the roi is unchanged

at the boundary between two media

- the principle of conservation of energy applies - if the reflected and transmitted intensities are added, the result must be the incident intensity - if IRC and ITC are added, the result must equal 100%

Two forms of harmonics are important in diagnostic sonography

- tissue harmonics and - contrast harmonics

read zoom has what 3 steps

- ultrasound system scans the anatomy - image is converted from analog to digital forma and is stored in the scan converter - the sonographer identifies the region of interest and the system reads and displays only the original data

write zoom has what 4 steps

- ultrasound system scans the anatomy and created an image - the image is converted from analog to digital forma and is stored in the scan converter - the sonographer identifies the region of interest, at that moment, the system discards all the existing data in the scan converter - the ultrasound system then rescans only the region of interest and writes new data into the scan converter

dedicated CW transducers do not use backing material, which results in :

- undampened transmitted signal - narrow bandwidth - high quality factor - higher sensitivity

the two most commonly used dictionaries are called ( color maps)

- velocity mode - variance mode

Breathing affects 2 venous flows:

- venous flow in the legs (return up) - venous return to the heart, which comprises venous flow from the IVC to the heart

PACS has three major advantages

- virtually instant access to archived studies - no degradation of data which often happens over extended time periods with analog archiving - store and forward telemedicine, the ability to electronically transmit images and reports to remote sites

as blood flows through the circulatory system, energy is lost in what 3 ways

- viscous loss - frictional loss - inertial loss

pulse repetition period and maximum imaging depth

- when the depth of view is shallow, the prp is short & vice vera ( PRP is directly related to max imaging depth)

Anatomy of a sound beam

-Focus -Near zone -Focal length -Far zone -Focal zone

what are the characteristics of damping material

-High degree of sound absorption -Acoustic impedance similar to PZT

what does the mechanical index depend on ?

-frequency of the transmitted sound -pressure (peak rarefaction-negative)

mechanical transducers have how many active elements

1

what are the three methods of focusing

1) external focusing = with a lens 2) internal focusing = with a curved active element 3) phased array focusing = with the electronics of the ultrasound system

what characteristics of a transducer determine the spread of the beam in the far field ? two factors combine to determine beam divergence

1) transducer diameter 2) frequency of the sound

what are the typical values for pulse repetition frequency

1,000 to 10,000Hz

what is the speed of sound in soft tissue

1,540 m/s (1.54 mm/µs) or (1.54 km/s)

what is the typical value for frequency?

2 MHz to 15 MHz

Elastography

A sonographic technique employed to evaluate a mass based on its stiffness, ultimately providing a prediction as to if the mass is more likely malignant or benign ( images are related to the mechanical properties of the tissue)

spectral analysis

A tool that breaks the complex signal into its basic "building blocks" and identifies the individual velocities that make up the reflected Doppler signal

kinetic energy is determined by what two factors

An object's mass and the speed at which it moves

characteristics of reverberation

Appears in multiples Appears as equally spaced Located parallel to the sound beam's main axis Located at ever-increasing depths

contrast harmonics

As an ultrasound pulse interacts with micro bubbles a small amount of energy is converted from the fundamental frequency to the harmonic frequency. contrast harmonics are created during reflection

Slice thickness phantom

Assesses slice thickness and its effect upon image accuracy Slice thickness determines elevational resolution

focusing

Concentrates the sound energy into a narrower beam and thus improves lateral resolution

Pulsed wave transducers

Creates a short duration electrical spike that travels through the wire and strikes the PZT crystal in the transducer

How is duty factor calculated?

DF(%) = ( pulse duration / prp ) x 100

Converting Sound Energy into Heat

Devices measure the output of ultrasound transducers by absorption, or the conversion of sound energy into heat

color flow doppler

Doppler shift information in a two-dimensional presentation superimposed on a real-time gray scale anatomic cross-sectional image.

how is intensity related to power?

Intensity is proportional to power ( directly related.. when a wave's power is doubled the intensity is doubled. related to amplitude squared)

pulsed vs continuous wave doppler

Pulsed - range resolution - sample volume - limited max velocity - nyquist - aliasing CW - range ambiguity - region of overlap - unlimited max velos - no aliasing

Compression of Dynamic Range

Reducing the total range of signals, from the smallest to the largest Changes gray scale mapping Decreased the dynamic range of signals the largest signal remains the largest the smallest remains the smallest the range of signals is reduced

Positive decibels

Report signals that are INCREASING in strength, or GETTING LARGER (when a wave's intensity doubles, the relative change is +3dB) ( when intensity increases ten-fold, the relative change is +10dB)

_____ is the most relevant intensity with respect to tissue heating

SPTA

for continuous wave ultrasound, the beam is always "on" and the pulse average and temporal average intensities are the same. thus,

SPTA= SPPA and SATA= SAPA

the rank of intensities from largest to smallest:

SPTP, Im, SPPA, SPTA, SATA

Because peak measurements are larger than average measurements ______ intensity has the highest value, and _______ has the lowest value.

SPTP, SATA

pixel

Short for "picture element" it is the fundamental unit of a digital image, typically a tiny square or dot which contains a single point of color of a larger image. smallest building block of a digital picture

what is frequency determined by?

Sound source only, not the medium through which the sound is traveling

Frame rate is determined by what two factors?

Sounds speed in the medium, depth of imaging (recall speed of sound in soft tissue is 1.54 km/s)

focal enhancement

Special form of enhancement in which a side to side region of an image appears brighter than tissues at other depths. aka focal banding -- has the same appearance as an incorrect TGC setting an entire horizontal region appears hyperechoic

What is Rayleigh scattering?

Special form of scattering that occurs when the structure's dimensions are much smaller than the beam's wavelength. rayleigh scattering redirects the sound wave equally in all directions.. in ultrasound the interaction of ultrasound and RBCs result in this type of scattering

Why is there a "2" in the Doppler equation?

The 2 represents the fact that there are actually two Doppler shifts during a clinical exam: first when sound from transducer strikes red blood cells, second when the reception of the reflected sound wave is received by the transducer

what do the colors in a velocity mode map mean?

The colors provide info. on FLOW DIRECTION and VELOCITY. Two different maps.

If two media are equally stiff but one of them is more dense what will result?

a lower speed in the denser material

dead zone

a place or period in which nothing happens or in which no life exists.

turbulent flow profiles may be seen downstream from

a significant stenosis in a vessel

incidence

a sound pulse strikes many tissue interfaces as it travels in the body. the angle at which the wave strikes the boundary determines the behavior of the pulse

cross talk

a special form of mirror image artifact, arises only with spectral doppler. it appears as identical doppler spectrum above and below the baseline

What is a decibel?

a unit used to measure the intensity of a sound or the power level of an electrical signal by comparing it with a given level on a logarithmic scale.

phased array means

adjustable or multiple focusing

adjustments to the output power and amplification of the system should alter the appearance of the image on the systems display and all output devices

adjustments on a single display device ( such as the brightness or contrast of a monitor ) alter the image on the particular device only

what is rejects effect on an image

affects all low level signals on the image, regardless of location. does not affect bright echos

what is the speed of sound in other media?

air = 300 water = 1480 metals = 2000-7000 ( as a general rule, sound travels fastest in solids, slower in liquids, and slowest in gases )

The most common artifact in encountered Doppler ultrasound is.....

aliasing

___, each electronic signal returning from the transducer is made larger. each signal undergoes an ____ of this

amplification ( or receiver gain), equal amount

after a transducer receives a sound wave during reception, the sound wave is converted into an electrical signal. the signal is sent to the ultrasound system where it is strengthened or

amplified

____ is the bigness of a wave. it is the difference between the maximum value and the average or undisturbed value. this is also the difference between the minimum and average.

amplitude

what is the difference between amplitude and peak to peak amplitude

amplitude is measured from the middle to the max, while peak to peak is the difference between the max and min values

Mirror image artifact

an artifact caused by sound bouncing off strong reflectors and causing a structure to appear on both sides of the reflector artifact is located deeper than the real structure

artifact is

an error in imaging.

temporal compounding is

an image processing technique that continues to display info from older images. with this, a number of previous frames are superimposed on the most current frame. a smoother image with reduced noise, higher signal to noise ratio, and improved image quality is produced

range ambiguity

an overlap between the transmit and receive beams (continuous wave doppler)

to move information from analog to digital requires a translator called an

analog to digital converter

typical values for normal incidence

angle must be 90 degrees

typical value for oblique incidence

anything but 90 degrees

the beam former also adjust electrical spike voltages to reduce lobe artifacts in a process called

apodization

edge shadow artifact

appears as a hypoechoic region extending down form the edge of a curved reflector.

comet tail artifact

appears as a solid hyperechoic line directed downward AKA ring down artifact

noise

appears as small amplitude echos and results from many sources including electrical interference, signal processing and spurious reflections

lobes

appears when sound energy is transmitted in a direction other than along the beams main axis

what is the limit at which aliasing appears and how is it determined?

appears when the doppler shift exceeds the nyquist limit. the nyquist limit is one half the pulsed repetition frequency

active element arrangement for annular transducer

arranged as circular rings with a common center

active element arrangement for convex transducer

arranged in a bow or arched line. aka curved or curvilinear array

active element arrangement for linear transducer

arranged in straight line

Modern transducers that contain multiple active elements are

arrays

in the circulatory system, the resistance vessels are called

arterioles

in diagnostic ultrasound we are often interested in the degree of ____ or the extent of ____

attenuation, amplification

what is it called when sound waves weaken

attenuation, u dumby

temporal average intensity ( Ita) is

averaged during the prp ( both on and off times)

pulsed average intensity ( Ipa) is

averaged only during the pulse duration ( on time)

spatial average intensity ( Isa) is

averaged over the cross sectional area of the beam

I m intensity is

averaged over the most intense half cycle

frequency compounding

averages the frequencies across the image to improve contrast resolution and reduce speckle

a negative doppler shift indicates flow ______ from the transducer

away

What allows some transducers to have better axial resolution than others?

ax res is determined by oulse length with shorter pulses yielding improved axial res.

what type of resolution is better in clinical imaging systems: lateral res or axial res

axial resolution is better than lateral because ultrasound pulses are shorter than they are wide

the ___ functions with array transducers during transmission and reception

beam former

a number called the ____ _____ ____ ( also called ____/____ factor) describes the spread of beam in space

beam uniformity coefficient .. sp/sa factor , which is unitless, with a value of 1 or greater

determinants of sound beams for the characteristic: lateral resolution

beam width

Why is frequency important in diagnostic sonography?

because it affects penetration and image quality.

the sound wave is considered audible sound when it is

between 20 Hz and 20 kHz (20,000Hz)

how many channels do most ultrasound systems have

between 31 and 256

what is the difference between wavelength and period

both describe a single cycle in a sound wave. wavelength refers to the length (distance) of the cycle. period refers to the time

Changes in pulser voltage modify the _______ of the entire image displayed.

brightness

what other terms describe stiffness

bulk modulus ( elasticity and compressibility is the opposite of stiff)

Doppler shift

change in the apparent frequency of a wave as observer and source move toward or away from each other ( when sound source and receiver move closer together or farther apart) ( AKA doppler frequency)

compressions effec on image

changes gray scale characteristics of the image

Acoustic variables

changes that occur within a medium as a result of sound traveling through that medium

a __ is the combination of the active elements, wire, and system electronics

channel

each pixels shade of gray is determined by what?

cluster of bits assigned to it. with increasing numbers of bits per pixel, more shades of gray appear on the image. images with many gray shades have better contrast resoution

on spectral displays, low frequency doppler shifts artifact from slowly moving anatomy are called ____. with color doppler, they are called _____

clutter, ghosting artifact

what are the units for half value layer thickness

cm

units for velocity .

cm/s

auto correlation or correlation function is the digital technique used to analyze

color flow doppler

color confetti occurs when

color gain is set inappropriately high

phase quadrature or quadrature detection

commonly used signal processing technique for bidirectional doppler

Without _________, every ultrasound image would become progressively darker with increasing depth.

compensation

dynamic range of components

component dynamic range transducer- 120db receiver- 100-120dB scan converter- 40-50 dB display- 20-30 db archive- 10-30dB

distance measurement accuracy

components of the ultrasound system used to measure distances also require periodic evaluation digital calipers should be checked in both the vertical and horizontal directions

is compression adjustable by the sonographer

compression modifies the gray scale mapping yes an ultrasound system has two kinds of compression. one that is integral to the system and cant be changes and the other that is adjustable.

there are areas of ______ and ______ in a sound wave

compression, rarefraction

how are information and images stored in PACS?

computer hard drives

modern digital scan converters use

computer technology

digital numbers

computer world, limited choices, discrete values

what is the acoustic variable pressure ?

concentration of force in an area units: pascals (Pa)

what is the acoustic variable density?

concentration of mass in a volume units: kg/cm^3

a transducer is any device that __________

converts one form of energy into another

refraction artifact

created when a sound pulse changes direction during transmission occurs when a sound wave strikes a boundary obliquely and the media on either side of the boundary have different propagation speeds

speed error

created when a sound wave propagates through a medium at a speed other than that of soft tissue. appear as a step off as if the structure is split or cut

the temperature at which the PZT is polarized is known as

curie temp or point

With internal focusing a _______ concentrates the sound energy into a narrower or tighter beam.

curves piezoelectric crystal

pulse duration is equal to the number of ____ in each pulse, multiplied by the ____ of each cycle.

cycles, period PD (us) = # cycles * period (us)

what are the units for amplitude?

dB pressure -- pascals density -- g/cm^3 partical motion -- cm, in, etc

attenuation is measured in ___ and reported as a ___ ____

dB, relative change( not absolute change)

what are the units for dynamic range

dB. it is a comparison, a relatice measurement, or a ratio between the largest and smalles signals that are measured

the __ helps create short pulses. as a result, sound pulses used for imaging contain a wide range of frequencies and are describes as ___ or ____

damping, wide bandwidth, broadband

what is the prefix, symbol and value for an exponent of 10^-1

deci, d, 1/10

the ___ is a common unit for measuring electrical signal strength and the brightness of images quantifiably

decibel (dB)

what are the units of attenuation?

decibels (dB)

the dynamic range of information ___ the more it id processed

decreases

the frequency of a transducer does not change. if the diameter of the new pzt crystal increases, what happens to the beam diameter in the far zone

decreases

higher frequency sound creates a

deeper focus

the depth at which variable compensation begins is known as the

delay

______ is a two-part process that changes the electrical signals within the receiver into a form more suitable for display on a monitor. a. amplification b. demodulation c. compression d. reject e. compensation

demodulation

the process of extracting the low doppler frequency from the transducer's carrier frequency is called

demodulation

Speed is determined by the ______ and ______ of the medium.

density and stiffness ( as stiffness ^ speed ^) (as density ^ speed -) ( stiffness has the greatest influence on speed.. low stiffness (air) sound moves slowly)

acoustic impedance is calculated by multiplying the ___ of a medium by the ___ at which sound travels in the medium

density, speed

beam divergence

describes the gradual spread of the ultrasound beam in the far field

Piezoelectric effect

describes the property of certain materials to create a voltage when they are mechanically deformed or when pressure is applied to them

Pulse inversion harmonics

designed to utilize the harmonic reflections (which are distortion free, eliminating distorted fundamental reflections)

what kind of interference occurs with out-phase waves?

destructive interference

inspiration's affect on blood flow

diaphragm moves down. chest cavity expands. negative thoracic pressure creates suction that increases venous return to the head. so venous flow from the head, arms, and vena cava increase. ( flow in the legs stop, because the diaphragm presses into the abdomen) ( thoracic pressure decreases)

what happens in the venous system with expiration

diaphragm moves upward, which increases flow below the abdomen, but stops flow above ( thoracic pressure increases)

color doppler uses ____ to convert measured velocities into colors that appear on the image

dictionary or lookup table

When a sound beam strikes a tissue boundary at a 90 degree angle reflection occurs only if the media on either side of the boundary have ________.

different impedances

heterogeneous

different; dissimilar -- portion of the tissue or an image that has differing echo characteristics throughout

When a wave reflects off an irregular surface, it radiates in more than one direction. This form of reflection is called _____ reflection or _______.

diffuse reflection or backscatter

modern beam formers use advanced microprocessor technology and produce signals in digital format. this is called

digital beam former

to move information from digital back to analog requires a translator called

digital to analog converter

the measurement of the Doppler frequency depends on the relationship between the

direction of blood flow and direction in which the sound propagates

How are pulse repetition period and depth of view related?

directly - as dov increases prp increases

Hyperechoic

displayed echoes that are relatively brighter than the surrounding tissue; may also be referred to as echogenic

what are the units of the half-value layer thickness?

distance : cm

Spatial intensity is related to _______

distance or space. an ultrasound beam does not have the same intensity at different locations

Reducing grating lobes

dividing each PZT element into small pieces -- called subdicing

nonmaleficence

do no harm

an advantage of selecting a lower frequency transducer for reducing aliasing

doppler shift is directly related to frequncy of the transducer. when measured in Hz at the same velo, lower doppler shifts occur with lower frequency transducers. lower frequency sound reduces the height of the doppler spectrum. lower shifts are less likely to exceed the nyquist limit, so they are less likely to alias

what is the relationship between the cosine 0 and the doppler shift

doppler shift is directly related to the cosine of the able between the direction of flow and the direction of sound

what is the relationship between the transmitted frequency and the doppler shift

doppler shift is directly related to the frequency of the transmitted sound

Creation of a frequency shift

doppler shifts are created when transmitted sound waves strike moving RBCs

3 dB means...

double

how can we determine the direction that the sound beam will transmit for linear phased arrays

draw a line that connects the electrical spikes& draw another line extending out of the transducer that is perpendicular to the first and that is the direction

when spectral doppler gain is too high what do you do

drop the gain to make it more black and white

what does decreased sensitivity mean

during reception, transducers with damping material are less able to convert low level sound reflections into meaningful electrical signals

________ is the percentage or fraction of time that the system transmits a pulse

duty factor

the ____ _____ describes the relationship of beam intensities with time

duty factor. the duty factor is a unitless number with a value between 0 and 1

a method of reporting the extent to which a signal can vary and still be accurately measured

dynamic range

All waves carry _______ from one location to another.

energy

What event provides energy to the circulating blood?

energy is imparted to blood by the contraction of the heart during systole

intertial energy loss

energy is lost whether the fluid speed changes or not

the beam diameter at 2 near zone lengths is

equal to the transducer diameter

the beam diameter at the transducer is

equal to the transducer diameter

anechoic

extreme form of hypoechoic, meaning entirely without echos

justice

fairness

The image created by a mechanical transducer is _____ or _____ shaped.

fan or sector

what image shape is given by linear phased arrays

fan or sector shaped

the __ indicates the max amount of compensation that the receiver can provide

far gain

When line density is low, _________ pulses create each image and the frame rate is ___________. temporal res is _____

few. high, high

bits per pixel: fewer vs more

fewer - fewer shades of grey - degraded contrast res more - more shades of gray - improved contrast res

images and their dynamic ranges: fewer shades vs more shades

fewer - few choices - black and white ( bistable) -narrow dynamic range - high contrast more shades - many choices - gray scale - wide dynamic range - low contrast

A narrow dynamic range means

fewer shades of gray ( high contrast image)

when the sonographer expands the sector size, also known as ______, more pulses are required to create an image. _______ decreases.

field of view, temporal resolution

beam focusing of mechanical transducer

fixed: conventional, mechanical, or fixed focusing

____, also called volume flow rate, indicates the volume of blood moving during a particular time (how much)

flow

Frictional energy loss occurs when?

flow energy is converted to heat as one object rubs against another. ( aka blood sliding across vessel walls)

pressure gradient increases when

flow increases or resistance increases

rayleigh scattering increases with what

frequency Rayleigh scattering = frequency ^4 ( when frequency doubles, rayleigh scattering is 16 times greater .. 2 x 2 x 2 x 2 = 16)

how does the frequency alter beam divergence in the far field?

frequency and beam divergence are inversely related

determinants of sound beams for the characteristic: frequency -- continuous wave

frequency of electrical signal from ultrasound system

The transmitted frequency is called the ____.

fundamental frequency

the image created by processing reflections that have the same frequency as the transmitted sound

fundamental image

Attenuation in lung tissue is [less than, greater than, the same as] attenuation in soft tissue.

greater than

reynolds number for turbulent flow is

greater than 2,000

the sound wave is considered ultrasound when it is

greater than 20 kHz

the ___ is twice the transmitted frequency

harmonic frequency ( also called second harmonic frequency)

the image created by processing reflections that are twice the fundamental frequency

harmonic image

why is it so significant that only strong sound beams create harmonic signals?

harmonics are produced along the main beam. beams that are most likely to create harmonics are least like to create artifacts

Viscous energy loss in blood is determined by

hematocrit

what are the units for temporal resolution?

hertz

what is frame rates units

hertz ( or per second)

When the PRP is short, the PRF is _____.

high

Shadows appear when the attenuation is ____ in the tissue above the shadow than in the surrounding tissue.

higher

what is the significance of attenuation in diagnostic sonography?

higher freq produces shorter pulses, which usually create more accurate images. however, higher freq sound attenuated more and is less capable of traveling to substantial depths. thus, there is a conflict between image accuracy and attenuation.. the doual is to use the highest freq that still provides images to the depth of the structures of clinical interest

with regard to resolution, what are the advantages of using a high frequency transducer

higher frequencies improve both axial and lateral resolution. axial resolution is improved in the entire image bc shorter pulses are associated with high freq sound lat res is improved in the far field only because high frequency pulses diverge less in the far field than low freq pulses. higher freq sound beams are narrower than lower freq beams

how does transducer frequency affect aliasing?

higher frequency transducers create more aliasing

disadvantage of adjusting scale to max to avoid aliasing

higher prf reduces sensitivity to low velocities. very high velocities, alaising artifacts still persist

When system imaging is shallow, PRF is ____, when it is deep, PRF is ____.

higher, lower

the time of flight is directly related to

how deep a sound pulse travels

shadowing artifact

hypoechoic or anechoic region extending . downward from a highly attenuation structure. shadows are the same color as the image background

With write magnification, temporal resolution is improved if what happens?

if the bottom of the region of interest is shallower than the original image's depth of view

edge enhancement

image processing method that makes pictures look sharper. creates subtle bright and dark highlights to better define a boarder

imaging vs non imaging transducers

imaging : - pulses with short duration and length - uses backing material to limit ringing - reduces sensitivity - wide bandwidth or broadband - lower q factor - improved axial resolation non imaging trasducers: - creates continuous wave or pulses with long duration and length - no backing material - increased sens. -narrow BW - higher q factor - cant create image

how does depth affect temporal resolution??

imaging depth and frame rate are inversely related

what system settings affect frame rate?

imaging depth and number of pulses per frame

___ is the acoustic resistance to sound traveling in a medium.

impedance ( tissue's impedance is calculated not measured) (AKA - characteristic impedance)

Larger diameter crystals

improve lateral resolution in the far field

lateral resolution ___ with multifocusing

improves

spatial resolution ___ with higher line density

improves

coded excitation

improves image quality, makes strongest pulse possible within FDA limits, provides higher SNR, improved axial, spatial, and contrast resolution, deeper penetration

eliminating aliasing

improves the ability to measure the maximum velocity with Doppler

what is the main advantage of multiple focal zones?

improves the accuracy of the individual images. with multi focus, each scan line has better lateral resolution

in what way does sound travel?

in a straight line

what is the relationship between ultrasound frequency and the attenuation coefficient in soft tissue?

in soft tissue, the attenuation coefficient in dB per cm is approximately one half of the ultrasonic frequency in MHz

the most effective way to eliminate aliasing on color flow image is to

increase the velocity scale

As frequency decreases, depth of penetration

increases

As the path length increases, the attenuation of ultrasound in soft tissue _______.

increases

the frequency of a transducer does not change. if the diameter of the new PZT crystal increases, what happens to the near zone length?

increases

the frequency of a transducer does not change. if the diameter of the new pzt crystal increases, what happens to the beam diameter in the near zone

increases

as the arch of the lens becomes more prominent, the degree of focusing _____

increases and the beam narrows in the focal zone

how does transducer output affect noise?

increases in output power also increases signal to noise ration increasing output power is the most common way to improve the signal to noise ratio

what does the matching layer do for a transducer

increases the efficiency of sound energy transfer between the active element and body - protects active element it is 1/4 the wavelength thick

with line density is high, the number of pulses per image ____, frame rate ____, and temporal resolution ____

increases, drops, decreases

range ambiguity artifact is eliminated by

increasing the PRP, which means deeper imaging and decreased PRF

__ is the concentration of energy in a sound beam.

intensity

___ is a beam's power to divide by its area

intensity

to calculate ___, divide the beams power by the beams cross sectional area.

intensity (W/cm^2) = power (W) / area (cm^2)

what is the relationship between intensity and amplitude?

intensity is proportional to amplitude squared. ( directly related... when amplitude is doubled, the intensity increases to four times its original value)

What is the relationship between wavelength and frequency?

inverse ( as long as the wave remains in one medium ) as frequency increases, wavelength decreases. the lower the frequency the longer the wave

what is the relationship between frame rate and time?

inversely related and reciprocals Tframe * frame rate = 1

B-mode displays are created as follows: as a sound pulse is emitted by the transducer, ___________. When a reflection returns to the transducer it is _______ and the ____________.

invisible dot, processed & the invisible dot is turned on

dynamic range

is a method of describing the extent to which a signal can vary and still maintain accuracy. think of it as the number of available choices

Crosstalk artifact

is a mirror image artifact that appears on a spectral doppler display

What is a preamplifier and what is its role in processing signals from the transducer during reception?

it is the process of improving the quality of a signal before it it is amplified. occurs often within the transducer itself. it is designed to prevent electronic noise from contaminating the tiny electrical signals created by the transducer's active elements during reception

velocity in a vessel increases when

it narrows. max velocity is where the vessel is the narrowest

what is the prefix, symbol and value for an exponent of 10^3

kilo, k, 1,000

at the depth of the ___, reflections are maximally compensated by the ultrasound system

knee

________ is when flow streamlines are aligned and parallel. This flow is characterized by layers of blood that travel at individual speeds and is associated with normal physiological states. a. parallel flow b. turbulent flow c. laminar flow d. phasic flow

laminar flow

Reflection is likely to occur when the dimension of the boundary is ______.

large; more than a few wavelengths of the sound

lobe artifact degrades

lateral resolution

refraction artifact degrades

lateral resolution

the piezoelectric materials used in clinical transducers

lead zirconate titanate ( PZT)

With deeper imaging, the listening time and the pulse repetition period _______.

lengthen

what is placed in front of the pzt crystal with external focusing

lens

les vs more aliasing

less - slower blood velocity - lower frequency transducer - shallow gate ( high PRF) more - faster blood velocity - higher frequency transducer - deep gate ( low PRF)

higher frequency sound produces a beam with

less divergence

larger diameter transducer produce a beam with

less divergence

fewer cycles in the pulse, cycles with shorter wavelengths

less ringing

a short pulse is created in what two ways

less ringing higher frequency

the sound wave is considered infrasound when it is

less than 20 Hz

although it is not always apparent, ultrasound systems can alter the spacing between sound beams. this is called ____

line density

linear behaviors

liner means proportional or symmetrical. linear systems respond in an eve manner

side lobes and grating lobes

lobes created by a single crystal transducer, such as mechanical probe are called side lobes. lobes created by array transducers are called grating lobes

why i log compression important in clinical ultrasound

log compression is adjustable where small differences in weak signals are displayed and seen as different gray scale levels.

the what of a number represents the number 10s that are multiplied to create the original number

logarithm or logs (hint count the zeros ... log of 100000 is 6.. there are 6 zeros.. don't be dumb) the significance of a logarithmic scale is that as the log is increased by 1, the actual number increases tenfold.. a log increase of 2 indicates that the signal is 100 times larger

as a general rule, _____ events are narrow bandwidth, whereas ______ events are wide bandwidth

long duration, short duration

When the system is imaging more deeply, the time from one pulse to the next is ______.

longer

Sound waves are _____ waves.

longitudinal

when the signal to noise ratio is ___, the strength of the signal is closer to the strength of the noise. the image contains a larger amount of visible contamination, and has less diagnostic value

low

pixel density: low vs high

low - few pixels per inch - larger pixels - less detailed image - lower spatial resolution high - many pixels per inch - smaller pixels - more detailed image - higher spatial resolution

because imaging probes use backing material and have a wide bandwidth, they are often referred to as ___

low Q

When the PRP is long the PRF is

low and the system listens for a longer time

Line density & temporal resolution compare low line density with high line density

low line density - widely spaced lines - fewer pulses per frame - shorter Tframe - higher frame rate - high temporal resolution - poor spatial resolution high line density - tightly packed lines - more pulses per frame - longer Tframe - lower frame rate - low temporal resolution - excellent spatial resolution

what is the typical resistance of veins

low resistance and low pressure

what is the relationship between the numerical value of the axial resolution and the image quality

lower numerical values of axial res indicate a shorter pulse

a shorter, dampened pulse has a ______ q factor a longer, undampened pulse has a ____ q factor

lower, higher

what is the speed of sound in different tissue types?

lung = 500 m/s fat = 1450 m/s soft tissue= 1540 m/s liver = 1560m/s blood =1560m/s muscle = 1600m/s tendon = 1700m/s bone = 3500m/s

with ____, the sonographer can improve visualization of anatomic detail by enlarging a portion of an image to fill the entire screen

magnification

scan converters

makes grayscale imaging possible by storing the image data then displays it on the screen

PRP determines

maximum imaging depth (depth of view)

temporal peak intensity is

maximum intensity in time

color doppler measures ___ velocity whereas spectral doppler measures ____ velocity

mean ( average) , peak

normal incidence

means that the incident sound beam strikes the boundary at exactly 90 degrees ( synonyms include : perpendicular, orthogonal, right angle, 90 degrees)

what is the acoustic variable distance?

measure of particle motion units: cm, feet, mile

Sound is a __________ wave in which particles in the medium move.

mechanical

the scan plane is created through

mechanical steering

how do we identify medium 1 and 2?

medium 1 is the medium in which sound is currently traveling medium 2 is the medium in which the sound is entering

Two media A and B have the same densities. The speed of sound in medium A is 10% higher than in medium B. Which medium has the higher acoustic impedance?

medium a's acoustic impedance is higher than medium b's. recall that impedance equals speed times density. since both media have the same density and medium a's speed is 10 percent higher, then medium a's impedance is 10% higher

what is the prefix, symbol and value for an exponent of 10^6

mega, M, 1,000,000

spatial compounding

method of using sonographic information from several different imaging angles to produce a single image

lateral resolution

minimum distance that two structures are separated by side-to-side or perpendicular to the sound beam that produces two distinct echoes

what are the units of axial resolution

mm

what are the units for lateral resolution

mm, cm, or any units of distance

what are the units for wavelength?

mm, meters, or any other unit of length.

the units for propagation speed are

mm/us, or m/s

what are the units for hydrostatic pressure

mmHg

obtuse angle

more than 90 degrees

More attenuation happens with what kind of distance and frequency? Less attenuation happens with?

more: longer distances, higher frequencies less: shorter distances, lower frequencies

kinetic energy is associated with

moving objects

higher frequency sound beams scatter ___ ___ than lower frequency beams

much more ; scattering is directly related to frequency

reverberation appear on the display as, and are caused by

multiple, equally spaced echos caused by the bouncing of sound wave between 2 strong reflectors positioned parallel to the ultrasound beam

when the attenuation coefficient is known, it is straightforward to determine the total attenuation of a sound wave as it travels. simple ____ the attenuation coefficient by the distance that sound wave traveled

multiply total attenuation (dB) = atten. coef. (dB/cm) x distance (cm)

field of view and temporal resolution compare narrow and wide sectors

narrow - fewer pulses per frame - shorter T frame - higher frame rate - superior temporal resolution wide sector - more pulses per frame - longer Tframe - lower frame rate - inferior temporal resolution

what are the important characteristics of contrast agents when used with harmonic imaging?

nature of the outer shell and the gas that fills the microbubbles

At superficial depths, reflections undergo a small, constant amount of compensation called :

near gain

Is frequency adjustable by the sonographer?

no

do low mechanical index sound beams create harmonics

no, because the relationship of expansion and contraction is linear

Is demodulation adjustable?

no, it is built in

Is axial resolution adjustable?

no, spatial pulse length is fixed

__ is described as a random and persistent disturbance that obscures or reduces a signal's clarity

noise

speckle

noise resulting from the constructive and destructive interference of small sound wavelets

PRP's relationship to period

none. it is only related to depth of view

Harmonic frequency sound waves arise from

nonlinear behavior

An alternative description of dynamic range is

number of choices

the beam diameter at the focus is

one half the transducer diameter

As sound waves propagate in the body, the move from

one medium into another & may change directions

axial resolution artifact creates

one reflection on the image from two closely spaced reflectors

Pulsed intensity refers to ______________.

only the transmit time ( pulse duration). a pulse ultrasound beam does not have the same intensity at different times during the pulse. pulsed is average intensity for the pulse duration only ( ignore listening time)

Blood cells in adjacent arteries and veins typically flow in _________ directions

opposite. when theses vessels undergo doppler evaluation, flow from one vessel is heard in the right earphone and the other in the left. arterial velocities are higher than venous velocities

hydrophone

or microprobe is similar to a small hypodermic needle with a tiny piece of PZT material attached to its end

nyquist limit

or nyquist frequency is the highest doppler frequency or velo that can be measured without the appearance of aliasing

range accuracy

or vertical depth calibration, describes the systems accuracy in placing reflectors at correct depths located parallel to the sound beam

pulser voltage synonyms

output gain, acoustic power, pulser power, energy output, transmitter output, power, or gain

what is the difference between output power and receiver gain? why is it important to appreciate this ?

output power : - affects image brightness by altering the strength of the sound pulse that the transducer sends to the body. - when an image is too dark, increasing output power creates a brighter image. increasing output power improves the signal to noise ration receiver gain: - aka amplification, alters the strength of the voltages in the receiver that the transducer created during reception. higher amp creates a brighter image

_______ has a bullet shaped profile. velocity is highest in the center of he lumen, and gradually decreases to its minimum at the vessel wall

parabolic flow

When blood cells are moving ___ to sound beam the entire velocity is measured

parallel

pressure energy has the ability to

perform work. pressure is a major form of energy for circulating blood and creates flow by overcoming resistance

_____ is the time it takes a wave to vibrate a single cycle, or the time from the start of one cycle to the start of the next

period

what are the 7 parameters of sound? (CW)

period, frequency, amplitude, power, intensity, wavelength, speed

parameters that describe both pulsed and continuous waves

period, frequency, wavelength, propagation speed

How do particles move in a transverse waves?

perpendicular to the wave propagation (ex: hold end of string and shake up and down)

synonyms for temporal compounding

persistence, temporal averaging

mechanical index and harmonics

pg 281

comparison of tissue and contrast harmonics

pg 283

how does sample volume depth affect the presence of aliasing?

pg 317

also occurs when blood moves with a variable velocity. blood accelerates and decelerates as a result of respiration ( often appears in the venous system)

phasic flow

how are linear phased arrays steered and focused

phasing

two important elements of digital scan converters are

pixel and bit

digital images : pixels and bits

pixels - image element - image detail - spatial res bits - computer memory - gray shades - contrast res

fill-in interpolation

places pixels where there is no signal information based on adjacent scan lines

_____ occurs when all of the layers and blood cells travel at the same velocity

plug flow

viscosity is measured in units of

poise

hypoechoic

portions of an image that are not as bright as surrounding tissues, or tissues that appear less bright than normal

Pre and post processing

preprocessing - time gain compensation - log compression - write magnification - persistence - spatial compounding - edge enhancement - fill in interpolation postprocessing - any change after freeze frame - black/white inversion - read magnification - contrast variation - 3d rendering

________ is a form of stored or potential energy.

pressure energy

the relationship between flow, resistance, and pressure gradient is defined by what equation

pressure gradient = flow x resistance

flow increases when

pressure gradient increases or resistance decreases

hydrostatic pressure

pressure related to the weight of blood pressing on a vessel measured at a height above or below heart level

how are pulse repetition frequency and depth of view related?

prf and depth of view are inversely related

an advantage of selecting a new view with shallower sample volume for reducing aliasing

prf increased, which increases the nyquist limit and reduces aliasing

When a sonographer adjusts a systems maximum imaging depth, the ______ is altered.

prf... more depth has lower prf

continuous wave transducer

produces a continuous electrical signal that excites the crystal

_ is the rate at which a sound wave travels through a medium

propagation speed

The height of the upward deflection is _______ the amplitude of the returning echo. ( A-mode)

proportional ( strong echos create tall spikes, whereas weak reflections create short spikes)

what does the case do for a transducer

protects the internal components of the transducer from damage. insulates the patient from electrical shock

what do the colors in variance mode map mean?

provides more info than velocity mode. in addition to direction and speed info, variance mode distinguishes laminar flow from turbulent flow

_______ occurs when blood moves with a variable velocity. blood accelerates and decelerates as a result of cardiac contraction( usually appears in arterial circulation)

pulsatile flow

Inertial energy loss occurs during three events

pulsatile flow(found in arterial system); phasic flow(found in venous system); velocity changes(changes at stenosis)

three basic forms of blood flow are

pulsatile, phasic, steady

to create an anatomic image, a sound ___ must travel to a reflector located in the body and return to the transducer. the travel time of this journey allows us to accurately position the reflector

pulse

____ _____ is the actual time form the start of a pulse to the end of that pulse.

pulse duration. ( it is a single transmit, talking, or on time)

____ is the number of pulses that an ultrasound system transmits into the body with each second

pulse repetition frequency - with regard to PRF, the # if cycles in each pulse is meaningless.. we are interested only in the # of pulses creates each second

____ is the time from the start of one pulse to the start of the next

pulse repetition period . it includes one pulse duration pulse one listening time

pulsed vs CW transducers

pulsed - at least 1 crystal - dampened PZT - low Q factor - wide bandwidth - lower sensitivity CW - at least 2 crystals - undampened PZT - high Q factor - narrow bandwidth - higher sensitivity

_____ creates and controls the electrical signals sent to the transducer that generate sound pulses. the ____ determines the amplitude, pulse repetition period, and pulse repetition frequency, while the ____ determines the firing delay patterns for phased array systems

pulser and beam former, pulser, beam former

the __ creates electrical signals that excite the transducer's PZT crystals and create sound beams, which functions during__________

pulser, transmission

Which type of pulse is more desirable in diagnostic imaging and why?

pulses of shorter length are desirable because they create more accurate images

how does the number of pulses in each image affect temporal resolution?

pulses per frame and frame rate are inversely related

how does the thickness of the pzt crystal affect frequency

pzt thickness and frequency are inversely related

a disadvantage to using continuous wave doppler for reducing aliasing

range ambiguity, because velocities along the entire line are being sampled

what are the typical values for impedance

range from 1,250,000rayls to 1,750,000 rayls (1.25 to 1.75 MRayls)

analog numbers

real world, unlimited # of choices, continuous range of values

the transducer receives reflections from anatomic reflectors in the body during _______ time.

receive or listening. the sonographer can alter the listening time when adjusting the imaging depth.

___ transforms the electrical signals from the transducer ( produced by the reflected sound) into a form suitable for display

receiver

During ______ the reflected sound pulse is converted into electricity.

reception

___ converts all negative voltages into positive

rectification

harmonic imaging

reduces an images noise content. its goal is to selectively distinguish meaningful reflections from noise increasing signal to noise ratio

what does the backing material (aka damping element) do for a transducer

reduces the ringing of the pzt. crystal dampening enhances axial resolution

apodization

reducing the strength of side and grating lobes the technique that varies the voltage to the individual elements to reduce grating lobes

sensitivity

refers to the ability to detect low level echos. it is elevated in a variety of two ways

As sound strikes a boundary, a portion of the wave's energy may be redirected, or _____ back to the sound source

reflected (reflection weakens the portion of the sound wave that continues in the forward direction)

___ of an ultrasound wave depends upon the difference in acoustic impedances of the two media at a boundary

reflection

____________ allows the sonographer to control whether low-level gray scale information within the data will appear on the displayed image.

reject

Decibels report _______

relative changes

As the path length increases, the attenuation coefficient of ultrasound in soft tissue _______.

remains the same

___ is the ability to create accurate images.

resolution

_____ predicts whether flow is laminar or turbulent. this for laminar flow is less than 1500

reynolds number

what does one of the acoustic variables have to do in order to be a sound wave?

rhythmically oscillate

contrast agents requirements

safe; metabolically inert; long lasting; strong reflectors of ultrasound; small enough to pass through capillaries

the ___ translates the information from the spoke format into the video format

scan converter

shadows may provide valuable diagnostic information that helps to characterize the tissue

shadowing is completely unrelated to the speed of sound in a medium

depth of view : shallow and deep imaging

shallow - shorter listening time - shorter PRP - higher PRF deep - longer listening time - longer PRP - lower PRF

piezoelectric materials change _____ when a voltage is applied to them, a process called the _____.

shape, reverse piezoelectric effect

When the system is imaging at shallow depths, the time from one pulse to the next is ______.

short

With shallower imaging, the listening time and the pulse repetition period ...

shorten

What type of pulse is more desirable in diagnostic imaging?

shorter duration pulses because they create images of greater accuracy

higher frequency sound

shorter wavelength & improves lateral resolution in the far field

Why is wavelength important in diagnostic ultrasound?

shorter wavelength are created by high frequency sound, which usually produces higher quality imaged which greater detail. ( we want high freq transducers!)

__________ is a comparison of the meaningful information in an image, compared to the amount of contamination

signal to noise

Transmission with Oblique Incidence

similarly MAY or MAY NOT OCCUR: If it does occur, the beam could travel in a straight line (angle of transmission) or the sound beam could bend/change direction (angle of refraction)

compare a single focus to multi for temporal res

single focus - one pulse per scan line - shorter Tframe - higher frame rate - better temporal res - poorer lateral res multi focus - many pulses per scan line - longer T frame - lower frame rate - diminished temporal resolution - improved lateral resolution

the mechanical transducer contains a ______, _____, __________ active element that is physically moved. this movement creates a scan plane

single, circular, disc-shaped

in the region of the ___, compensation corrects for the effects of increasing attenuation that results from increasing path length

slope

persistence is most effective with

slow moving structures

Higher pixel density is achieved with ____ pixels.

smaller

what is the main advantage of high line density?

smaller gaps between lines improve the accuracy of each individual image. improves spatial (detail) resolution

axial resolution

smallest distance at which two pins parallel to the sound beam are displayed as two distinct echoes uses pins that are parallel to the sound beam

___ places a smooth line around the bumps and evens them out

smoothing or enveloping

multipath artifact is created when

sound pulses glance off a second structure on the way to or from the primary reflector

what is pulse duration determined by?

sound source ( not the medium)

What is power determined by?

sound source (initially)

What is axial resolution determined by?

spatial pulse length ( shorter pulse improves axial resolution )

digital displays

spatial resolution is related to pixel density. spatial resolution improves with a large number of pixels in an image of fixed size which is called: high pixel density

When the boundary is smooth and the sound is reflected in only one direction in an organized manner. this reflection is called..

specular ( occurs when a light wave strikes a mirror )

what are the two forms of reflection

specular and diffuse

____, which is purely a magnitude, indicates the distance that a red blood cell moves in 1 second

speed (cm/s)

what characteristics of a medium determine the speed of sound in that medium?

stiffness and density

the _____ archives the ultrasound studies. Typical devices include a hard drive, CD, DVD, photographs, etc...

storage

for b mode, the brightness of the dot indicates the

strength of the reflection : the reason it is called brightness mode

methods to eliminate lobes

subdicing and apodization

systems with dynamic frequency tuning use only the high frequency part of the reflected pulse's bandwidth to create the ____ of the image because higher freq sound has superior axial res

superficial portion

the __ protects the sensitive electrical components in the receiver from the high voltages created during transmission

switch

sensitivity is also assessed when the sonographer adjusts the

systems controls to change echo brightness from barely visible to full bright

______ describes the ability to precisely position moving structures from instant to instant

temporal resolution ( temp res is excelent when a system produces many frames per second)

Bidirectional Doppler

the Doppler device that can detect positive and negative Doppler shifts

registration accuracy

the ability of the system to place reflections in proper positions while imaging from different orientations

axial resolution

the ability to accurately identify reflectors that are arranged parallel to the ultrasound beam's main axis

what does the PZT or active element do for a transducer

the active element is shaped like a coin. the PZT is 1/2 wavelength thick

what is the mechanical index?

the amount of contrast harmonics produced is estimated by this number

which is better to use while examining a carotid artery, a 7.5 or 3.0 MHz transducer?

the carotid artery is superficial structure. a 7.5 freq transducter is better because the higher the freq transducer produces the better image. we can use the higher freq bc the structure is superficial and attenuation is of little concern.

focal zones

the focus is the depth at which the intensity is the highest and the beam is the narrows . the focal zone surrounds the focus. lateral resolution is excellent here

What nonlinear behavior of a microbubble creates contrast harmonics?

the microbubbles shrink and expand within the sound wave, which creates contrast harmonics a behavior known as resonance

attenuation coefficient

the number of decibels of attenuation that occurs when sound travels one centimeter ( the advantage of describing sound weakening with attenuation coefficient is that its value remains constant, regardless of how far the sound travels. aka... if the attenuation coefficient of sound wave is 2dB/cm, that per cm value will remain constant regardless of the distance that the wave actually travels) (EX sound travels 5cm. the attenuation coefficient remains 2bD/cm. the total attenuation of the beam is 10 dB ( 5cm x 2dB/cm)

hematocrit is

the percentage of blood made up of RBCs ( normal value is ~45%.. with anemia, this is reduced)

intensity reflection coefficient (IRC)

the percentage of the intensity that bounces back when a sound beam strikes the boundary between two media

If the sound beam and flow direction are not parallel, what determines how much of the velocity is measured?

the percentage of the true velocity that is measured depends on the cosine of the angle between the sound beam and the direction of motion

what is the bernoulli's principle derived from

the principle of the conservation of energy ( the sum of all forms of energy is the same everywhere)

in addition to controlling the strength of the transmitted sound wave, the pulser determines the time between one voltage spike and the next

the pulse repetition period

bandwidth

the range of frequencies within a pulse. it is the difference between the highest and lowest frequency

compensation is performed without altering

the ranking between the signals: the largest remains the largest

is there another form of nonlinear behavior that further minimizes distortion with tissue harmonics

the relationship between sound beam strength and harmonic creation is nonlinear

Snell's Law of Refraction

the relationship of the angle of incidence to the angle of refraction States that the product of the index of refraction of a medium and the sine of the angle of incidence equals the product of the index of refraction of a second medium and the sine of the angle of refraction.

horizontal calibration

the systems ability to place echos in their correct position when the reflector s are perpendicular to the sound beam

Inertia definition

the tendency of a fluid to resist changes in its velocity

during transmission, _____ transforms electrical energy into acoustic energy. during reception, it converts the returning acoustic energy into electrical energy

the transducer

at angles other than 0 and 180 degrees, only a portion of ____ is measured

the true velocity

attempts to standardize transducer output have resulted in two measurements tha appear on the screens of modern ultrasound systems:

thermal or mechanical index

how can we distinguish bidirectional flow from aliasing with color doppler

they appear different.

determinants of sound beams for the characteristic: frequency -- pulsed wave

thickness of ceramic and speed of sound in ceramic

elevational resolution is determined by

thickness of the imaging plane

slice thickness

thickness of the section in the patient that contributes to echo signals on any one image aka section thickness artifact or partial volume artifact

what does the electrical shield do for a transducer

thin metal barrier lining the inside of the case. prevent electrical signals in the air from entering the transducer . helps prevent electrical noise from contaminating the clinically important electrical signal

thin half value layer vs thick

thin: high freq sound, media with high attenuation rate thick: low freq sound, media with low attenuation rate

record and archiving techniques : types of data storage

this is stupid pg 260

dedicated continuous wave

this is the pedoff probe. has only one crystal that sends AND receives. no anatomic imaging may be done with this transducer . has higher sensitivity. they detect low amplitude reflections and small doppler shifts

synonyms for reject

threshold, suppression

Tissue vibration associated with turbulence is called a ?

thrill

what is period reported in?

time (microseconds)

Intensities may be reported in various ways with respect to _____ and _______.

time and space

the x axis of a dopper spectrum represnts ___ , while the y-axis represents

time, velocity

what are synonyms for compensation?

time-gain compensation (TGC), depth gain compensation (DGC), swept gain

what is the rule that defines the relationship between frequency and wavelength of sound in soft tissue?

to find wavelength, divide 1.54mm by frequency MHz ( in soft tissue)

a positive doppler shift indicates flow ____ the transducer

towards

how does transducer diameter affect the focal depth

transducer diameter and focal depth are directly related

ultrasound systems contain these six major components

transducer, pulser and beam former, receiver, display, storage, master synchronizer

During ______ electrical energy from the system is converted into sound.

transmission

____ is critical to ultrasound's ability to image structures located deep in the body

transmission

what is compensations effect on image

treats echos differently depending upon the depth from which they arise

T or F. In a given medium, attenuation is unrelated to the speed of sound.

true. attenuation and propagation speed are unrelated

_____ is characterized by chaotic flow patterns in many different directions and at many speeds. the streamlines are often obliterated

turbulent flow

Spectral broadening is associated with _______.

turbulent flow, where it has a wider range of velocities and doppler shifts within the sample volume

how many times is compression performed

twice first the compression keeps the electrical signal levels within the accuracy range of the system's electronics. second, compression keeps an image's gray scale content within the range of detection by the human eye. humans can distinguish approx 20 shades of gray

When one reflector is twice as deep as another reflector, the pulses time-of-flight is _______ for the deeper reflector.

twice as long

Decibels require ______ intensities which are ___

two, the reference or starting level and the actual level at the time of measurement

continuous wave doppler requires how many crystals in the transducer

two. one constantly transmits ultrasonic energy while a second crystals continuously receives reflections from the blood

When a spike pattern is a straight line, an ___________ sound beam is created.

unfocused

sine means

unitless number with a value form 0-1

a-mode appears as a series of

upward spikes

Ohm's Law

used to describe fluid and electrical systems - pressure in a fluid system is called voltage in an electrical system - flow in a fluid system is called current

a pulse of ultrasound is propagating in soft tissue, such as live. the pulse strikes a boundary with a different soft tissue at normal incidence. what portion of the intensity is reflected back toward the transducer? why?

very small percent of sound ( less than 1%) at the boundary between two soft tissues) since impedances are similar, very little reflection occurs

Why are microbubbles strong scatterers of sound waves?

vibrating stucture can produce large oscillations or resonance

When the pulser is set to a low-voltage, the PZT of the transducer vibrates gently, and a __ sound beam is transmitted into the body

weak

how do veins adapt to increased inflow during periods of exercise?

when inflow is increased, the cross sectional shape changes, which allows veins to accommodate large volumes with increased pressure. as a vein becomes more round, the resistance to flow decreases

what is interference (for sound)?

when more than one sound beam travel in a medium and can arrive at the same place at the same time. the waves then loose their individual characteristics and combine to form a single wave.

attenuation and reflection

when sound waves strike a boundary, a portion of the energy may be redirected or reflected remaining portion that continues is weaker

what is the relationship between actual velocity and measured velocity when blood moves parallel to the sound beam

when the angle is 0( 1, toward the transducer) or 180 ( -1 away from transducer) flow is parallel to sound beam

what is the relationship between actual and measured velocities when blood moves perpendicular to the sound beam

when the direction of flow is perpendicular ( 90) to the sound beam, the measured velocity is zero. so doppler shifts and velocity cannot be measured with perpendicular incidence

under what conditions will the transmission angle be greater than the incident angle?

when the speed of medium 2 is greater than medium 1 ( speed 1 < speed 2)

under what conditions will the transmission angle be less than the incident angle?

when the speed of medium 2 is less than 1 ( speed 1 > speed 2)


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