ultrasound physics boards (edelman)
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.
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)
crosstralk results from either
- doppler gain set to high - an incident angle near 90 degrees between the sound beam and the flow direction
four commonly accepted principles of health care ethics include
- respect for autonomy - nonmaleficence - beneficence - justice
What should the sonographer do when first meeting a patient?
- respectfully introduce yourself - identify the patient
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
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
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
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
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
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
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
what does the mechanical index depend on ?
-frequency of the transmitted sound -pressure (peak rarefaction-negative)
coded excitation provides
-higher signal-to-noise ratio -improved axial resolution -improved spatial resolution -improved contrast resolution -deeper penetration
Doppler packet disadvantages:
-more time needed to acquire data - reduced frame rate -decreased temporal resolution
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)
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%
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)
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.
acoustic impedance = _____ x ______
Impedance = density (kg/cm3 ) x propagation speed (m/s)
Is amplitude adjustable?
Initial amplitude is, yes.
Is power adjustable?
Initial power is adjustable yes via the U/S machine.
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)
what is the relationship between the prp and prf
Inversely related and reciprocals ( the longer the prp --> lower prf) PRF= 1/PRP
Is propagation speed adjustable?
No *Speed changes only when the wave travels from one medium to a different medium.
What are the 3 acoustic variables?
Pressure (P), density (ρ), and distance (particle vibration)
range error artifact
Propagation speed errors are also called
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
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
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)
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
oblique incidence
occurs when the incident sound beam strikes the boundary at any angle other than 90 degrees ( not at right angles or perpendicular)
homogeneous
of the same kind; alike --- portion of the tissue or an image that has similar echo characteristics throughout
electrical resistance is reported in units of
ohms
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
-10 dB means
one tenth
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
_____ 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
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
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
___ transforms the electrical signals from the transducer ( produced by the reflected sound) into a form suitable for display
receiver
___ 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
the ____ ____ is an important tissue property that influences the amount of reflection
acoustic impedance
Phased array always means:
adjustable or multi-focus
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
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
linear phased arrays crystals amount, shape, & width
amount: 100-300 shape: rectangular and narrow width: 1/4 to 1/2 of sound's wavelength
___, 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
the y axis for a mode displays
amplitude
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
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
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
what are the units for attenuation coefficient
dB/cm
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
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
when the sonographer expands the sector size, also known as ______, more pulses are required to create an image. _______ decreases.
field of view, temporal resolution
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)
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 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 frequency and period
inversely related (p * f = 1) --> reciprocal
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
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)
what happens if the crystal is damaged for mechanical transducers
whole image is lost
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
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
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
primary limitation of persistence
reduction in the displayed frame rate, which reduces temporal resolution
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
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 )
____________ 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
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
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 duty factor determined by?
sound source
what is pulse duration determined by?
sound source ( not the medium)
What is power determined by?
sound source (initially)
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
What is axial resolution determined by?
spatial pulse length ( shorter pulse improves axial resolution )
__ 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
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
what is the parameter that is determined by the medium only
speed
____, which is purely a magnitude, indicates the distance that a red blood cell moves in 1 second
speed (cm/s)
what is the difference spatial pulse length and pulse duration
spl = the distance while pd = the time
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)
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)
10 dB means...
ten times larger
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
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
Increase wall filter doppler output
the bottom one
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.
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
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)
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
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
____ 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
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
resonant frequency
vibrates freely for a long time at a single frequency
Why are microbubbles strong scatterers of sound waves?
vibrating stucture can produce large oscillations or resonance
units for flow
volume divided by time L/min 5L/min
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
__ is the distance or length of one complete cycle.
wavelength
what is the parameter determined by both the medium and sound source
wavelength
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
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)
hydrostatic pressure of a supine patient
~zero at all locations
focus or focal point
~the location where the beam reaches its narrowest --> minimum diameter.
Far Zone (Fraunhofer Zone)
~the region or zone deeper than the focus, beyond the near field. ( where the beam diverges or spreads out )
two ways to avoid aliasing are
- raise the nyquist limit - reduce the doppler shift
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)
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
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
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
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.
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 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
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
characteristic of speed error
- correct number of reflectors - improper depth - appears as a step off
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)
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)
what are the five additional parameters that describe pulsed sound?
- pulse duration - spatial pulse length - pulse repetition period - pulse repetition frequency - duty factor
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 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
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
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
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)
factors the affect beam divergence in the far field for less divergence
- larger diameter - higher frequency
deep focus and focal depth
- larger diameter PZT - higher frequency
Shallow imaging ( duty factors)
- less listening - shorter prp - higher prf - higher df
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
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 long pulses
- many cycles in the pulse - cycles with longer wavelengths
what are two characteristics that create pulses of long duration?
- many cycles in the pulse or - individual cycles with long periods
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)
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)
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 are the 5 parameters determined by just the sound source?
- period - frequency - amplitude - power - intensity
what two forms are there for laminar flow
- plug flow - parabolic flow
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
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%
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
Two forms of harmonics are important in diagnostic sonography
- tissue harmonics and - contrast harmonics
what are the two components of pulse repetition period? which one can the sonographer change
- transmit time (pulse duration--> sonographer cannot change) - receive time
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
doppler phatom
- vibrating string - moving belt - flow phantom
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
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)
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)
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)
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.
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
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
mechanical transducers have how many active elements
1
what is the value for an exponent of 10^0
1
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 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
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
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)
what is the typical value for frequency?
2 MHz to 15 MHz
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)
what is the log of 10,000
4 ( 10*4)
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
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.
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
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)
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
kinetic energy is determined by what two factors
An object's mass and the speed at which it moves
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
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
how can we distinguish bidirectional flow from aliasing with color doppler
they appear different.
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)
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)
viscosity describes
thickness of a fluid
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)
pulse duration is equal to the number of ____ in each pulse, multiplied by the ____ of each cycle.
cycles, period PD (us) = # cycles * period (us)
units for compression
dB
risk benefit relationship
Benefits to the patient must outweigh the risks of the exam
what are the units for amplification
dB
what are the units for compensation?
dB
what are the units for amplitude?
dB pressure -- pascals density -- g/cm^3 partical motion -- cm, in, etc
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.
attenuation is measured in ___ and reported as a ___ ____
dB, relative change( not absolute change)
Pulsed wave transducers
Creates a short duration electrical spike that travels through the wire and strikes the PZT crystal in the transducer
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
digital scan converter
Computer memory that stores echo information a process called digitizing
focusing
Concentrates the sound energy into a narrower beam and thus improves lateral resolution
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
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
How is duty factor calculated?
DF(%) = ( pulse duration / prp ) x 100
what is depth of view
Describes the maximum distance into the body that an ultrasound system is imaging
Converting Sound Energy into Heat
Devices measure the output of ultrasound transducers by absorption, or the conversion of sound energy into heat
beneficence
Doing good or causing good to be done; kindly action
color flow doppler
Doppler shift information in a two-dimensional presentation superimposed on a real-time gray scale anatomic cross-sectional image.
what are the units for frequency?
Hertz (Hz) 1 cycle/second = 1Hz
the 13 microsecond rule
For every 13 MICROSECONDS of GO-RETURN TIME, the object creating the reflection is 1 CM DEEPER in SOFT TISSUE
how does frequency affect focal depth?
Frequency and focal depth are directly related.
contrast agents
Gas bubbles encapsulated in a shell
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
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
Temporal resolution artifact
Low frame rates. Less accurate positioning of reflectors in motion. -the ability to precisely position a moving structure
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 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.
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
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
spatial resolution artifact
Related to the overall detail in an image. determined by line density, axial resolution, and lateral resolution
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
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 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
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 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.
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
quality factor
a unitless number that is inversely related to bandwidth
refraction
The bending of a wave as it passes at an angle from one medium to another ( refraction is transmission with a bend)
what do the colors in a velocity mode map mean?
The colors provide info. on FLOW DIRECTION and VELOCITY. Two different maps.
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
the ___ functions with array transducers during transmission and reception
beam former
Compensation creates an image that is
Uniformly bright from top to bottom
what are the units for pulse duration?
Units of time like microsecond (μs).
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
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
If two media are equally stiff but one of them is more dense what will result?
a lower speed in the denser material
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
dead zone
a place or period in which nothing happens or in which no life exists.
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
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
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
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
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
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
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
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
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
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)
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
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
receiver corrects for attenuation with a process called
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
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) (%)
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
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
how does transducer diameter affect beam divergence in the far field
crystal diameter and beam divergence are inversely related
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
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
_ 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
isoechoic
describes structures with equal echo brightness
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
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
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
__ presents processed data.
display
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
what is the relationship between the velocity of blood and doppler shift?
doppler shift is directly related to the velocity of the blood cells
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
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
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
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
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)
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
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
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
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
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
-3dB means
half
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
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
Shadows appear when the attenuation is ____ in the tissue above the shadow than in the surrounding tissue.
higher
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
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
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
what happens if a crystal is damaged for linear phased array tranducers
inconsistent or erratic beam steering and focusing
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
what is the typical resistance of veins
low resistance and low pressure
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
acute angle
less than 90 degrees
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 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
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)
advantage of adjusting scale to max to avoid aliasing
max prf raises the nyquist limit which allows for less alaising
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
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
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
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
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
Can amplification alone make an image of uniform brightness from top to bottom?
no
Is frequency adjustable by the sonographer?
no
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
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
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
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 waves arise from
nonlinear behavior
harmonic frequency sound arises from
nonlinear behavior
non linear behavior
nonlinear means irregular or disproportionate. a system is nonlinear when it behaves unevenly
An alternative description of dynamic range is
number of choices
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
Angles with a measure other than 90 degrees are _______?
oblique (includes acute & obtuse)
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
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
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)
decibels are a ____. the measured level is divided by the starting level
ratio
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
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.
analog scan converter
the first type of scan converter and made gray scale imaging possible
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
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
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)
pixel density
the number of picture elements per inch
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.
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
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
