Ultrasound Physics Registry ~Edelman

♥NOTE: If no info is provided on whether a sound beam is focused or unfocused, choose the lower intensity limit (for unfocused beams, 100mW/cm2) as it is safe under all conditions of focusing

NOTE

♥NOTE: the packet size must balance between accurate velocity measurement and temp resolution. This is why color dopp measures MEAN velocity.

NOTE

♥NOTE: we still use 2MHz to 10MHz tx to perform a doppler us study, but the doppler shift ranges from 20-20000Hz

NOTE

♥NOTE: for lateral res, look to see whether the pins are perpendicular to the sound beam

NOTE...

NOTE: AIUM Statement-Vitro studies results are real; although important scientifically, "reports of in vitro studies which claim direct clinical significance should be viewed with caution"

NOTE: AIUM Statement

Note: Very high US intensities; genetic alteration or damage which may be lethal to cells.

NOTE: bioeffects

♥NOTE: Using epidemiology studies has shown that diagnostic US has no adverse effects on fetal outcome or birth weight or any other measurement.

NOTE: epidemiology studies

NOTE: transient caviation: Do not confuse cavitation bioeffects with contrast agents. The words are similar, but the gaseous nuclei that we are referring to here exist naturally in the body.

NOTE: transient cavitation

♥What is temp res determined by? (2 factors)

~Imaging depth-shallower image depth is better & has improved temp res ~Number of pulses per frame-less pulses are better & has higher frame rate w/ improved temp res

Equation for Transmitted Intensity

~Incident intensity x intensity transmission Coefficient

What is the equation for reflection w/ normal incidence

~Intensity Reflection Coefficient (%)= {z2-z1/z2+z1}2

Relationship of intensity to power.

~Intensity is proportional (directly related), to the power. (as one goes up, the other goes up)

What 2 questions are asked to determine the effect on temp res?

~Is the image shallower? ~Is the image comprised of fewer pulses?...

♥What is the LARRD equation?

~LARRD resolution(mm)=spatial pulse length(mm)/2

♥High fq sound improves LARRD where in the image? ♥ LATA where in the image?

~LARRD: everywhere in the image ~LATA: in the far field only

♥What are the crystals, # and shape of linear switched or Sequential arrays?

~Large tx w approximately 200 rectangular shapped elements arranged in a line.

♥Using multi-focus degrades temp reso but improves :

~Lateral resolution...

What are the typical dimensional units? (3)

~Length ~ARea ~Volume

What are the 3 specific methods for focus?

~Lens (external focusing) ~Curved Piezoelectric Crystal (internal focusing) ~Electronic Focusing (adjustable...Phased Array)

What happens when the image depth is shallower?

~Less time req to make each image ~more frames created each second ~frame rate increases ~temp res improves...

♥Imaging tx are an example of _____-Q tx when compared to therapeutic tx's.

~Low-Q

♥Which mode (a, b, or m) is the only mode that displays the chnging position of reflectors with respect to time?

~M-mode

Pulser mode in pulsed wave arrays:

~Many elements are fired for each us pulse...therefore: ~♥for each sound pulse, many short duration electrical spikes are required - one electrical spike per fired element.

What are the 6 interconnected components of the pulsed echo system?

~Master synchronizer ~Transducer ~Pulser ~Receiver ~Display ~Storage...

♥What are the four commandments of intensity?

~May be reported in various ways w respect to time and space ~Intensity is the key parameter w regard to bioeffects ~Peak is greater than average ♥~For CW sound, SPTA=SPPA and SATA=SAPA

♥What is lateral resolution?

~Minimum distance where two rods are displayed as 2 sep images is lateral resolution...

Both IRC & ITC units: range from:

~NONE, they are unitless ~0%-100%, or 0-1.0

♥How are the elements fired with the phased array?

~Nearly simultaneously.

♥Do continuous wave tx require damping material?

~No they do not.

♥Can LARRD be changed by sonog?

~No, a new tx is needed to change LARRD

What does refraction require? (2)

~Oblique incidence & different speeds

What information is processed by a pulsed echo system? (4)

~Time of flight ~Strength ~Direction ~Frequency (for Doppler)...

♥Defn of Refraction

~Transmission with a bend. It is a change in direction as sound transmits from one medium to another.

What is the equation for Intensity Transmission Coefficient (%)

~Transmitted Intensity/Incident Intensity X 100 = 100% - Intensity Reflection Coefficient

♥What does diffraction appear as? (shape) Also called:

~V-shaped wave ~Huygen's wavelet.

Facts regarding phasic flow:

~Venous, respiration, low rate, lower pressure

Intensities are reported in units of:

~W/cm2

What is the units used for intensities?

~W/cm2

What units do all intensity descriptions have?

~W/cm2

Defn of interference:

~When 2 waves overlap at the same location and the same instant in time, they combine one new wave.

Defn of Diffuse reflection:

~When a boundary is rough, reflected sound is disorganized and random.

♥When does diffraction appear?

~When produced by a tiny source.

♥What axis' are used with B-Mode What is on each axis?

~X (reflector depth) ♥~Z Axis (brightness of the dot) ~Z is measured by relfection amplitude.

♥What do the x & y axis' represent with M-Mode?

~X represents time ~Y axis represents reflector depth, and is measured by the pulses time-of-flight.

Dfn of array?

~a collection of active elements in a single tx...

♥How do the crystals, steering & focusing work with the phased array?

~a collection of electric pulses is delivered to all of the tx elements in various patterns. ~(this is why it is considered electronic)

Describe linear array: What are the 2 types of linear array?

~a collection of elements in a line ~Linear switched (sequential) array & linear phased array

What is demodulation performed by?

~a demodulator

♥How does the switched arrays work in order to improve lateral resolution?

~a few elements (5-10) are fired at exactly the same time to create a narrow directional beam.

♥What is dynamic aperture?

~a form of electronic receive, electronic focusing...

What is pressure energy?

~a form of potiential or stored energy that has the ablity to perform work

♥What is a byte?

~a group of 8 bits is byte. ~2bytes (16 bits) is a word

What is a binary number?

~a group of bits ~a series of zeroes & ones

What is an annular array tx?

~a group of ringed elements (bulls eye) with a common center

Defn Decibels

~a logarithmic scale

Explain how a digital scan converter works:

~a microporcessor digitizes images. This converts the image data into numbers which are stored to memory.

What happens when spatial compounding is used?

~artifacts (speckle and clutter) are reduced ~spatial res (detail) is improved ~temporal res (frame rate) is reduced ~shadow are reduced or eliminated

♥Why is "small sound good"??

~artifacts are created when the sound beam is larger than the reflector...

♥HINT: If you encounter a question that says "with a-mode, b-mode, and m-mode, what...." how should you interpret the question?

~as if it was saying "with anatomic imaging"

Conservation of energy exists where?

~at a boundary

♥Lateral res is best at which zone? Why

~at the focus or one near zone length (folcal depth) from the tx b/c the sound beam is narrowest at that point.

♥All sound, regardless of the frequency, travels _______ through any specific medium.

~at the same speed.

♥What is the current method for color flow dopp?

~autocorrelation or correlation function (FFt is not fast enough)

♥Color dopp reports? (also called)

~average velocities (also called mean velocities

♥HINT: if you encounter a numerical question,

~axial resolution is best in tx w the highest fq and the fewest # of cycles per pulse. ~axial resolution is worst in tx w the lowest fq & the largest # of cycles per pulse.

♥Why are LATA not as good as LARRD resolution?

~b/c US pulses are wider than they are short

What is hydrostatic pressure?

~b/c blood has weight ~hydrostatic pressure equals the weight of blood pressing on the vessel from heart level to the point of measurement

What results with frequency compounding is used?

~b/c images are averaged, it improves signal-to-noise ratio. ~reducing speckle & clutter artifacts ~improves spatial resolution (detail)

What is hydrostatic pressure in standing patient? (equation is either + or - from true pressure)

~ -50mmHg at fingertip w hand elevated above head ~-30mmHg at head ~0 mmHg at heart ~ 75mmHg at knee ~100mmHg at ankle

♥Attenuation in blood is > or < in soft tissue?

~ <

Define of an acoustic variable

~ A-V Identify which waves are sound waves.

♥2-d images may be referred to as what? or what? Why>

~ B-scans or B-Modes ~b/c they are in gray scale

What happens to the frames with spatial compounding?

~ frames are averaged, improving signal-to-noise ratio.

What is M-mode? Also called:

~ production of "squiggly lines" that represent the motion of the reflecting body surfaces as they occur in time.

What is the equation for quality factor?

~ quality factor=resonant frequency (MHz)/bandwidth (MHz)

♥Snells Law is: Equation:

~ the physics of refraction are described by Snells law. ~sin (transmission angle)/sin(incident angle)= propagation speed 2/propagation speed 1

What happens if the tx is damaged with linear switched tx?

~ there will be a dropout extending from superficial to deep.

♥♥On the exam pay attention to the subtle difference in the terms depth & ____

~ total distance

♥Rule for soft tissue and wavelength

~ wavelength(mm)= 1.54 mm/us/ frequency (MHz)

♥With shorter pulses the number is ______ and the image is ______ _______

~# is smaller ~the image is more accurate

What is the equation for Spatial Pulse Length (mm)

~#of cycles X wavelength (mm)

What is range accuracy measurement?

~(vertical depth calibration)... ~Vertical

What is dynamic frequency tuning?

~b/c imaging pulses contain a wide range of fq (wide bandwidth or broadband) ~with dynamic fq tuning, higher fq create shallow parts of the image and lower fq create deeper parts

♥What is most likely to happen with bone?

~b/c it is an absorber, temp elevation at tissue-bone interface is more likely

Why does harmonics work?

~b/c the fundamental beam undergoes distortion (creating a bad image), while the harmonic signal distorts to a lesser extent.

♥Why does shadowing occur?

~b/c the us beam is unable to pass through a structure bc it has a higher than usual attenuation ~background color (too few reflections on the scan) ~absence of true anatomy on scan in the region of the shadow. ...

Wide long, thick beams are?? (good or bad)

~bad ~b/c long pulses create artifacts & degrade axial resolution ~wice pulses create artifacts and degrade lateral resolution ~thick pulses create artifacts & degrade elevational resolution...

What is the equation of bandwidth?

~bandwidth(Hz)=maximum frequency-minimum frequency

♥What are some man-made pzt materials? Natural pzt materials?

~barium titanate, lead metaniobate, lead titanate, & ♥lead zirconate titanate PZT) ~quartz, rochelle salts, tourmaline

♥Higher fq pulsed US has what kind of beams in the far field compared to lower fq?

~barrower beams compared to lower fq in the far field.

♥Lateral resolution is = the:

~beam diameter.

♥For phased array systems, the pulser is also called:

~beam former

What does electronic slope create?

~beam steering

What does electronic curvature create?

~beam transmit focusing.

♥Short pulses create ______ images...(better or worse)

~better

What is the typical value range for impedence?

~between 1,250,000 & 1,750,000 rayles ~or....1.25Mrayls-1.75Mrayls

♥The matching layer has an impendence _____ those of skin & the active element to _____ the % of transmitted US bet the active element and the skin.

~between.....to increase the %

An example of an image after scan converter?

~black on white image can be turned into a white-on-black image.

♥What is considered energy gradient?

~blood flows when the total fluid energy at one location differs from the total fluid energy at another location.

♥What is the relationship betw FFT and autocorrelation?

~both are digital techniques that are performed by computers.

Defn of pulsatile flow & phasic flow:

~both move with variable velocities

What does output power affect? ♥

~brightness by adjusting the strength of the sound pulse sent to the body by the tx. ~♥When the image is too bright due to high output power, the lateral and long resolution degrade

♥Compared to therapeutic tx, imaging tx are wide bandwidth or ________. This is because:

~broadband ~imaging tx use backing material

Explain transient cavitation

~bubbles expand during rarefactions and the bubbles burst. ~depends upon the pressure of ultrasound pulses (MPa)

Explain stable cavitation

~bubbles tend to oscillate when exposed to acoustic waves of small amplitude ~bubbles do not burst ~bubbles that are a few micrometers in diameter will double in size ~bubbles intercept, reradiate & absorb acoustic energy

How is range ambiguity artifact cured?

~by lowering the PRF (aka..imaging deeper) b/c the PRF is too high and coded excitation..

With mechanical tx..how must the focus be changed?

~can only be changed by changing the tx...

♥Explain temp elevation via absorbtion...

~can result from interaction of bio tissue and US. ~2nd mode of thermal injury may result from localized scattering of acoustic energy, especially with Rayleigh scattering.

What happens w annular array tx has defective crystals?

~causes horizontal (side-to-side) band of dropout.

With parabolic flow, layers travel at individual speeds, speeds being the highest in the:

~center of the lumen

♥What are some synonyms for Main Frequency?

~center, resonant, primary, natural frequency.

♥What are some other terms for PZT? (3)

~ceramic, active element, or crystal

What does a scan converter do?

~changes the data format from US penetrations (spokes) to that of the display. ~made gray scale displays possible by first storing the image data and then displaying it.

♥What is the effect of compression on the image?

~changes the gray scale mapping

Dynamic Aperture:

~changes the number of elements in the array that recv reflections. The deeper the reflection (longer go-return times), the more array elements are used to receive.

♥What is the purpose of demodulation?

~changes the signal's form to one more suitable for TV display. ~Cannot be adjusted

How can artifacts be eliminated in the image?

~changing the view ...

♥what setting has the greatest affect on jet size?

~color doppler gain

What do the colors represent with color?

~colors represent information on flow direction.

♥Defn of channel

~combination of electronic circuitry, the wire and the element

What is the doppler phantom?

~commercially available, contains static simulated vessels as well as dynamic simulated vessels at a variety of angles...

♥What does the Master Synchronizer do?

~communicates with all individual components of the US system. ♥Organizes and times their functions, so as to operate as a single integrated system....

Sound is a series of:

~compressions and rarefactions

What does digital pertain to?

~computer world. ~a variable attains only discrete values such as: ~measuring weight on a digital scale.

Define pressure:

~concentration of force within an area

Define of density & unit

~concentration of mass within a volume kg/cm3

♥What is the makeup of the annular phased array tx?

~concentric rings cut from the same circular slab of pzt. The array looks like a bulls eye target.

Pulser mode in Continuous wave tx: equation

~constant elec signal in the form of a sine wave ~electrical frequency=US frequency

♥The hourglass shape of the sound beam is the result of what?

~constructive and destructive interference of the many sound wavelets emitted from these numerous sound sources.

♥What type of focusing does a mechanical tx have?

~conventional or fixed ~Curvature (internal) of the pzt or an acoustic lens (external) focuses the beam at a specific depth.

Role of the tx?

~converts elec into acoustic energy during transmission ~converts returning acoustic into elect energy during reception...

What does rectification do?

~corrects for or elimates negative voltages

♥Speckle is created by?

~created by interference effect of scattered sound...

Dynamic fq tuning:

~creates different parts of the image w diff fq reflections. Shallow parts of the image are created w higher fq.

What does non-linear behavior create?

~creates harmonics. ~As sound waves travel in body, a small amount of energy is converted from the fundamental freq to the harmonic fq due to this non-linear behavior

What is the definition of sound?

~creates images by sending short bursts of energy into the body.

Frequency compounding:

~creates multiple, entire images from different sub-bands. The images are then averaged

What is harmonics?

~creates scans from sound reflections at twice the transmitted frequency. ~♥Harmonics are multiples of the tx freq

♥What is the purpose of the beam former? What is the approx time delays?

~creates the electronic patterns. ~Delays are approximately 10 nanoseconds.

Explain rendering

~creation of an image based on 3D data acquired during the exam. It provides an element of realism to an image. ~considered postprocessing

♥What is the units of dynamic range?

~dB, a relative measurement

♥What are 6 characteristics of an imaging transducer?

~damping material is effective (backing material) ~short pulse length & duration ~low sensitivity ~low Q ~decreased output power

As fq increases, the numerical value of larrd resolution _____, this means that we have improved larrd resolution & higher quality images with ______.

~decreases ~high fq tx

♥What is the Y-axis Measured by

~deflection ~measured by reflection amplitude

♥A convex or "D-shaped firing patern" creates what type of beam?

~defocused/ divergent beam

♥What happens to a piezolelectric material when voltage is applied to them?

~deform or change shape (reverse piezoelectric effect)

♥As temp res improves (higher frame rate), image quality may:

~degrade ...

Pulser signals depend on what?

~depend on the system and the tx

♥What is temp res determined by?

~depends only upon frame rate ~more images per second improves temp resolution...

♥Lateral resolution will vary with :

~depth

♥What is the defn of sound beam divergence?

~describes the spread of the sound beam in the deep far zone.

What is viscosity? Units? ♥

~describes the thickness of a fluid ♥~Poise

Divergence is determined by:

~diameter of ceramic & freq of sound

Focal length is determined by:

~diameter of ceramic & frequency of sound

In regards to pressure: what happens with inspiration?

~diaphragm descends into the abd cavity: ~pressure within the abd cavity increases; venous flow in legs decreases ~pressure within the thorax decreases; venous return to heart increases

♥Defn doppler shift? Units;

~difference between received and transmitted frequencies ~units in Hertz, cycles per second

♥Reflection occurs only if the two media at the boundary have:

~different acoustic impendances

♥What is DICOM?

~digital imaging and communications in medicine ~provides standards or guidelines for medical imaging networks.

Color dopp provides info regarding:

~direction of flow. ~it is semi-quantitative, so knowledge of angle is not especially important

What is focal depth? Also called?

~distance from the tx face to the focus. ~aka focal length or near zone length.

Defn of focal depth:

~distance from tx to the focal point

What is the equation for time of flight

~distance to boundary (mm)= go return time(μs)/2

What is the equation for time of flight in soft tissue?

~distance to boundary (mm)=time (μs)X 0.77mm/μs

♥♥Speed =

~distance/time

What does the AIUM 100mm Water-Filled Phantom evaluate?

~does not evaluate gray scale but does evaluate axial, lateral, horizontal, registration, verical registation, and dead zone...

What are the 2 causes of cross talk?

~dopp gain set too high (electronic cross-talk) ~Incident angle near 90degrees when flow is at focus...

♥When one reflector is twice as deep as another reflector, the pulse's time-of-flight is _____ for the deeper reflector. Aka....it is _______

~doubled ~aka...the time-of-flight will be increased by a factor of two.

♥Why is it more difficult to study in vivo?

~due to absorbtion (most), scattering, and reflection...

What are 2 advantages & 2 disadvantages of having more pulses in the packet?

~+ greater accurance of the velocity measurement ~+Sensitivity to low flows is also increased with many pulses in the packet ~-more time is required to acquire the info ~-frame rate and temp reso are reduced

♥What are the typical values of axial resolution?

~.05-.5mm

♥Example of refraction...A sound wave strikes a boundary at normal incidence. The impedances of the two media are identical. What % of the sound wave is refracted?

~0....refraction requires oblique incidence.

What is the typical value in soft tissue for wavelength?

~0.1-0.8mm

♥What are the cosines of each of the following? ~0 degree ~60 degrees ~90 degrees

~0degrees = cosine of 1 (most accurate) ~60degrees= cosine of 0.5 (oblique incidence) ~90degrees = cosine of 0 (normal incidence)

♥In biological media, typically less than ___% of the incident US energy is reflected at a soft-tissue boundary between different biological media. Such as with _____ & ____

~1% ~such as with blood and muscle.

-10dB=

~1/10th of original value

♥The thickness of the PZT crystal = ____ of the wavelength of the sound crystal

~1/2

♥What is the beam diameter for an unfocused cont. wave disc tx at... ♥at the end of the near zone: ♥at two near zone lengths:

~1/2 the tx diamter (aka aperture) ~is = the tx diameter

♥The thickness of the matching layer is ____ of the wavelength of sound in the matching layer.

~1/4

♥The matching layer is ______ thick.

~1/4 wavelength

♥Binary numbers are based on 2, while decimal numbers are based on :

~10

♥10dB means:

~10 times bigger or more intense

What voltage does the pulser use to excite pzt crystals?

~10-500Volts

When IRC and ITC are added, the result is:

~100%

♥What is the number of crystals in a continuous wave doppler?

~2 crystals in the transducer (one is constantly transmitting & the other is continuously receiving)

♥3dB means:

~2 times bigger (2 times bigger final intensity)

♥What are the typical values of doppler shift?

~20Hz-10kHz (audible) ~created when sound reflects off of red blood cells

What focusing does phased array technology provide?

~dynamic, variable focusing or multi-focusing.

What is the disadvantage of cont wave dopp?

~echoes arise from entire length of overlap betw the transmit and receive beams (called range ambiguity)

Frequency (CW) is determined by:

~electronic frequency

Describe convex, curved, or curvilinear array tx: What are the 2 types

~elements arranged in an arc. ~Convex switched (sequential) array & convex pahsed array

♥1/12 dimensional arrays allow focusing in the plane of the beam width. What does it improve?

~elevational resolution: makes a thinner slice ...

♥What is high pass filter?

~elininates low magnitude dopp shifts that are created from moving anatomy rather than rbc's...

What is kinetic energy?

~energy assoc with a moving object

What is systole?

~energy is imparted to blood by the contraction of the heart (lft ventricle)

What are some synonyms for color power doppler?

~energy mode, color angio

Sound carries:

~energy, not matter, from place to place.

♥HINT: Lateral res is approximately:

~equal to beam diameter

♥What does tissue equivalent phantom evaluate?

~evaluates gray scale b/c it has velocity of 1540m/s...

♥What is amplifications effect upon the image?

~every signal is treated identically (uniform amplification). Thus: ♥~amplification changes the brightness of the entire image

What is the image shape with a mechanical tx? ♥how do the scan lines appear with depth?

~fan or sector-shaped... ~♥Scan lines diverge or seperate with depth

Image shape for the phased array is:

~fan/sector shaped.

♥Image shape of annular phased array?

~fan/sector-shaped

♥What is another name for piezoelectric materials?

~ferroelectric material

Low line density: Pulse FR Temp reso

~fewer pulses ~higher frame rate ~better temp reso...

Narrow sector... Pulses? Frame rate? Temp reso?

~fewer pulses ~higher frame rate ~better temp reso...

Single focus... Pulses used? Frame rate? Temp res?

~fewer pulses ~higher frame rate ~better temp resolution...

Echoes arising from superficial structures are filtered to process only: Bc?

~filter higher fq b/c higher fq make better images

♥How to calculate the number of gray shades that a collection of bits can represent:

~find out how many bits are assigned to each pixel ~multiply the number 2 by itself the same number of times as there are bits.

What are the 2 general types of focus?

~fixed (aka conventional or mechanical) ~adjustable by electronics (called phased array)

♥Which tx have the poorest lateral resolution? Why?

~fixed focus tx. ~b/c it cannot be adjusted

What type of focusing does a linear switched array have

~fixed focusing. Where it has a lens (external) or curved cyrsal (internal)

Describe laminar flow:

~flow streamlines are aligned and parellel ~♥may have a plug or parabolic patterns (found in normal physiological states)

Defn of steady flow?

~fluid moving at a constant speed or velocity

When does cross talk occur?

~found in Doppler only...

Attenuation coefficient is related to:

~frequency

♥Rayleigh scattering is related to?

~frequency

What is the equation for frequency with pulsed tx?

~frequency(MHz)=materials propagation speed (mm/us)/ 2X thickness(mm)

♥What are the 3 forms of energy loss?

~frictional loss ~viscous loss ~inertial loss

What occurs with friction?

~frictional losses occur when one object rubs against another (blood sliding across vessels walls)

Explain contrast agents (micro bubbles)

~gas entrapped in a shell ~Contrast agents have a different acoustic fingerprint than blood or tissue ~They "light up" blood or chambers or vessels

♥Examples for 13microsecond rule: 13μs...reflector depth: 1cm...total distance: 26μs...reflector depth:2cm...total distance: 52μs...reflector depth 4cm...total distance: 130μs..ref depth 10cm...total distance:

~2cm total distance ~4cm ~8cm ~20cm

♥6dB means: ♥20dB means: ♥30dB means:

~2x2= 4times bigger than original ~10x10= Final is 100 times bigger ~10x10x10=Final is 1000 times bigger

♥The angle of the incident sound beam is 30degrees. What is the angle of reflection?

~30degrees (the angle of reflection =the angle of incidence)...

What is the approx propagation speed for pzt material:

~4-6mm/us

♥What percentage of reflection occurs at a bone-tissue interface?

~50%

♥Specular reflections are well seen when sound strikes the reflector at:

~90degrees

♥What boundary creates the greatest reflection ?

~99% at an air-tissue interface.

♥What is the gold standard for eval of diagnostic accuracy

~A "perfect" technique for example MRI or angiograpy, that we deem 100% accurate to which our us results are compared....

Defn of pulsed sound:

~A collection of cycles that travel together. ~Analogy: a train w/ individual cars move as ONE.

♥Defn of impendence Units

~A number assoc with a MEDIUM. It is calculated, not measured ~Rayls (Z)

♥Defn Piezoelectric Effect:

~A property of certain materials to create a voltage when pressure is applied, or when the material is mechanically deformed.

What is a hydrophone?♥

~A small needle w a pzt crystal at its end. It attachess to an oscilloscope and displays acoustic signals recvd by the crystal. ~Can quantitate amplitude, period, pulse duration & pulse rep period.

What is Reynolds number?

~A unitless number indicating whether flow is laminar or turbulent.

♥What is the effect of rejection on the image?

~Affects all low level signals everywhere on the image, but does not affect bright echoes. ~Can be adjusted

Temporal refers to:

~All time (transmit and receive)

What organization compiles scientific info?

~American Institute of Ultrasound in Med (AIUM)...

♥What are the functions of the receiver? (hint: alphabetical order)

~Amplification ~compensation ~compression ~demodulation ~rejection

What are the three parameters that describe a sound beams strength?

~Amplitude ~Power ~Intensity

What is A-Mode?

~Amplitude mode ~A-Mode provides very precise measurements of distances between the probe & the reflector.

♥What is considered Oblique Incidence?

~Anything other than 90degrees; not at right angles.

What is another term used for diffuse reflection?

~Backscatter

What is bidirectional Doppler analyzed with?

~Bidirectional dopp is analyzed with phase quadrature processing.

What is a BIT?

~Binary Digit ~the smallest amount of digital storage ~a bit is bistable ; it has a value of either zero or one.

♥All 3 of the "bigness parameters" _________ be changed by the sonographer

~CAN be changed

What is turbulent flow associated with?

~Cardiovascular pathology and increased velocities (ie...stenosis)

♥What are 2 types of disinfectants used:

~Cidex or gluteradehyde

What is the effect of compensation on the image?

~Compensation makes all echoes from similar reflectors appear identical regardless of their depth ~♥Uniform brightness

What happens with multi-focused in regards to lateral resolution?

~generally it improves lateral res but will degrade temporal res (because it reduces frame rate & temp reso)...

♥When do microbubbles typically get larger? What happens to bubble?

~get larger during rarefactions ~causes the bubble to be sheared apart and creates cavitation.

♥Positive decibels means:

~getting bigger/ the intensity is increasing

♥Negative decibels means:

~getting smaller

♥What is speckle?

~grainy appearance not directly from reflections from tissues in the shallow part of the image....

♥What is speckle?

~grainy, or granular appearance in tissues that are really homogeneous. ~speckle does not represent actual tissue texture

♥What is subdicing?

~grating lobe artifact can be reduced or cured by dividing each element into even smaller, miniature pieces. ...

♥What is apodization:

~grating lobes are further reduced by exciting the subdiced elements with different voltages. ~subelements closer to the center of the sound beam are excited w higher voltages, while the outermost subelements, further away from the center of the beam, are excited with lower voltages. ...

When the mdium 2 is faster than medium 1 the angle of transmission will be:

~greater

Narrow-beamed tx provide _____ quality imaging & good _______

~high quality imaging ~good lateral resolution

What is aliasing?

~high velocities appear negative. W pulsed dopp, high velocity measurements are inaccurate if the pulsed dopp sampling rate (PRF) is too low in comparison to measrued blood velocity.

♥The faster the active materials prop speed, the _____ the tx fq.

~higher

The thinner the active element in pulsed tx, the ______ the tx resonant or natural fq. Ex...

~higher ~think of a crystal glass

♥What happens when the output power is increased with the pulser?

~higher elec voltages are created that strike the pzt cyrstal; increasing the sound intensity created by the tx and sent into the patient

Lower fq signals are used to image deeper structures b/c?

~higher fq have attenuated & are no longer present.

Larger diameter crystals producing _____ frequency sound produce beams that diverge ___ in the far field:

~higher frequency ~less in the far field

Total attenuation increases with: (2)

~higher frequency ~longer path length

♥What are the effects for transient cavitation?

~highly localized viloent effects: ....enormous pressures-shock wave, mechanical stress ...colossal temperatures-thousands of degrees

♥What are the horiz & vertical axes of the doppler spectrum?

~horiz (x-axis) is Time ~vertical (y-axis) is Doppler shift/ velocity

With the mechanical tx, which plans does focusing occur?

~horizontal and the vertical planes.

What is the role for continuous wave dopp?

~id's highest velocity jets anywhere along the length of the ultrasound beam. Range ambiguity. No aliasing.

♥When the size of an image increases:

~if number of pixels is unchanged: pixel size increases (read mag)

What happens with phased array if the cyrstals are defective?

~if one element malfunctions, the steering & focusing become erratic.

♥What occurs when pzt is depolarized?

~if pzt is heated above 360degrees C or 680F)..it will lose its piezoelectricity.

Defn scattering:

~if the boundary betw two media has irregularities with a size similar to or a bit smaller than the pulse's wavelength, then the wave may be chaotically redirected in all directions.

♥What occurs with propagation speed errors? also called

~if the media through which the US travels doesn't propagate at 1.54km/s, then the assumed relationship betw time and distance is invalid. ~speed errors appear as a step-off, split, or cut...

What is the equation for impendence

~impendance (rayls)=density(kg/m3)X propagation speed (m/s)

♥As temp res degrades (lower frame rate), image quality may

~improve...

♥What is the 13microsecond rule?

~in soft tissue, every 13us of go-return time means the reflector is 1cm deeper in the body.

What tissue is cavitation more likely to occur?

~in the lungs

♥Where are harmonics created?

~in the tissues, not in the tx or receiver.

♥Diff between in-vivo & in-vitro

~in-vivo= living ~in-vitro= in a glass...

♥With oblique incidence...Reflection angle=

~incident angle ♥(this is NOT snells law)

What is the equation for intensities?

~incident intensity= reflected intensity + transmitted intensity

If image is too dark....first...

~increase receiver gain

♥What occurs with frequency when flow is ♥towards tx? ♥Away?

~increased frequency ~decreased frequency

♥What can cause viscosity of blood? (2)

~increased hematocrit (polycythemia) or hemoglobin (erythrocytosis) causes increased blood viscosity.

♥What are some advantages of color power dopp?

~increased sensitivity to low flows (venous flow, or flow in small vessels) ~not affected by dopp angles, unless the angle=90 ~no aliasing

♥As frequency of sound increases, the attenuation coefficient...

~increases

What is the purpose of the amplification? Also called? Units?

~increases the strength of all electrical signals in the recvr prior to further processing ~also called the receiver gain ~dB

♥♥ Describe Digital-Analog (D-A) converter

~info in the scan converter is digital, but some displays are analog. ~the image data ust be re-converted to analog from prior to display ~an example of D-A is an ipod.

Describe color flow dopp:

~instead of measureing velocities at one location (w pulsed dopp) or along a single cursor line (w CW dopp), color flow is a form of 2-d dopp. ~the dopp shifts are coded into colors and superimposed on a 2d image

♥What is speckle created by?

~interference effects of scattered sound, both constructive & destructive, from the many tiny tissue reflectors

What is the threshold for transient cavitation?

~is only 10% higher than the pressure for stable cavitaion.

Why is spectral analysis performed?

~is performed to extract or id the individual fq making up the complex signal. It is used to interpret individual velocities in the signal.

♥The more bits per pixel, the more shades of gray, and the better:

~is the contrast resolution

♥When is autocorrelation used?

~is used with color dopp bc of the enormous amount of dopp info that requires processing. ~is slightly less accurate, but substantially faster than FFT.

What is the diaphragms position with: Inspiration Expiration Phasic Flow

~Diaphragm presses into the abdomen ~presses into the thorax ~pressures in the 2 compartments vary with inspiration & expiration and venous flow varies as well, phasicity.

What does doppler fq depend on?

~Direction.

♥What is Fill-In Interpolation?

~it improves image detail (spatial resolution) by filling in the missing data, especially for deeper parts of the image.

Purpose of compression:

~keeps signals within the operating range of the systems elec and the gray scale within the range of what the human eye can see. ~♥ Allows us to see all gray scales ~♥Decreases the dynamic range of the signals

Reynold number: less than 1,500= between 1500 & 2,000= greater than 2,000=

~laminar ~??? ~turbulent

Deep focus=

~large diameter ~high frequency

♥Convex sequential array place a :

~large footprint on the patient...

When converting units, as the unit gets _______, the number must get _________

~larger, smaller

♥What is LATA?

~lateral resolution

♥In the far field beam is wide & lateral resolution is _____ with small diameter, _____ frequency sound.

~lateral resolution is worst ~low frequency sound.

With variance mode: the color map also varies side-to-side: each side represents?

~left side: the flow laminar or parabolic, uniform and smooth. Often normal flow ~Right side: the flow turbulent or disturbed, random and chaotic. Often assoc with pathology.

When medium 2 is slower the angle of transmission will be:

~less

♥In soft tissue, lower frequency results in: ♥We penetrate further with high or low frequency sound?

~less attenuation ~lower frequency sound

LARRD resolution improves with:

~less ringing (fewer cycles in pulse) ~higher fq sound

what do vector arrays combine?

~linear sequential and linear phased array technologies...

♥What are the 5 synonyms for axial resolution? Mnemonic for these terms?

~longitudinal ~axial ~range ~radial ~depth ~LARRD resolution

What is required for the following: Reflection w normal incidence: Reflection w oblique incidence: Transmission Refraction

~look for diff impendances ~we Do Not Know ~derive this from reflection info ~look for oblique incidence & diff speeds.

Images with what type of line density are most improved with fill-in interpolation?

~low line density are most improved with fill-in interpolation. ~they have higher frame rate (good temp res)

Smaller diameter crystals producing ____ fq sound produce beams that diverge subtantially in the _____ field.

~lower ~far field

Which fq provides deeper penetration?

~lower fq

♥Compared to beams with shallow focus, beams with a deep focus have a ______ intensity at the focus

~lower intensity

♥Velocity is:

~magnitude and direction

Speed is:

~magnitude only

♥What is edge enhancement?

~makes an image appear sharper; most uselful to emphasize the boundary betw different tissues.

♥Explain gray scale display:

~many levels of brightness (white, light gray, medium gray, dark gray, black, etc)

What are four factors under sonog control that affect temp res?

~max imaging depth ~# of pulses per scan line (multi focus system) ~sector size ~line density (lines per angle of sector)...

♥Attenuation ultimately limits what??

~maximum depth from which meaningful reflections are obtained.

Highest velocity is at the point of:

~maximum narrowing

What does the diff colors represent with gray scale?

~may represent different signal strengths ~low contrast, wide dynamic range, improved contrast resolution.

♥Defn of signal: NOise?

~meaningful portion of data ~inaccurate portion of the data which degrades the quality of information

Define of distance & units

~measure of particle motion cm, ft, miles

Explain Nonthermal (cavitation) mechanism with Gaseous nuclei:

~microbubbles may be excited by US. This takes the form of shrinking & expanding of the bubble. ~♥ Potential of near total energy absorption where the nublei exist may lead to thermal injury.

Multi focused... PUlses used Frame rate? Temp res?

~more pulses ~lower frame rate ~worse temp res...

Wide sector... Pulses? Frame rate? Temp reso?

~more pulses ~lower frame rate ~worse temp reso...

High line density: PUlse FR Temp reso

~more pulses ~lower frame rate ~worse temp resolution...

♥Higher fq tx need: tgc Lower fq tx need: tgc

~more tgc ~less tgc

What happens when the image depth is deeper with more pulses?

~more time req to make each image ~fewer frames created each second ~frame rate decreases ~temp res is reduced...

What is a reverberation?

~multiple echoes appearing on the display as a result of US "ping-ponging" between 2 reflectors. ~looks like a ladder or a veneitian blind...

♥What are the 4 requirements of periodic evaluation?

~multiple evals of the systems components ~repairs ~preventative maintenance ~record keeping...

♥What is a dopp packet? also called?

~multiple us pulses are needed to accurately determine rbc velocities by Dopp. ~Ensemble length

♥What is the beam width rule?

~narrow beams create better images

♥In what 3 ways does focusing alter the beam?

~narrower "waist" in the US beam ~shallower focus ~smaller focal zone

♥What occurs when there is less sound beam divergence? (4)

~narrower beam in far field ~larger diameter active element ~high frequency ~improved lateral resolution in far field

In regards to the TGC, where is the near field with the buttons? Far field?

~near field is at the top (shallow) ~far field is at the bottom (deep)

Where is focusing most effective?

~near field& the focal zone

♥What is NAS?

~network storage devices ~high storage capacity ~economical ~used in PACS systems

♥What are some limitations to color power dopp?

~no measurement of velocity or direction ~slower freame rates when compared to conventional color flow dopp ~susceptible to motion of tx, patient or soft tissues, this is called flashed artifact.

When both medium 1 & 2 are the same speed the transmission will show:

~no refraction

Refraction cannot happen with: (2)

~normal incidence or with identical propagation speeds.

What are the synonymbs for transient cavitation? HINT for cavitation?

~normal or interial cavitation ~mnemonic for types of transient cavitation; "TIN"

Define of frequency ♥Unit?

~number of certain events that occur in a particular time duration ♥~per second, 1/second, Hertz, Hz

♥When does slice thickness occur? This is also called?

~occurs when beam has a greater width than the reflector... ~Elevational resolution

Explain hyperechoic enhancement

~occurs when the medium through which the sound travels has a lower attenuation rate than soft tissue ~since the attenuation is less, echoes returning from deeper areas appear brighter on the display ~ hyperechoic...

♥Defn specular reflection:

~occurs when there is a reflection from a smooth reflector.

♥Fetal soft tissue adjacent to bone are:

~of great concern for thermal elevation

What are the limitations of epidemiological studies...

~often retrospecitive (looking at past information) ~ambiquities (justification for exam, gestational age, # of exams, exposure and mode ~other risk factors (maternal age, nutrition, smoking, alcohol, drugs.

-3dB=

~one half of the original value

♥What is a bistable display?

~only has 2 choices; black or white, on or off, high contrast, narrow dynamic range, poor contrast resolution.

♥How many sound pulses are created with a phased array?

~only one sound pulse is created.

♥What happens when 2 side by side structures are closer together tan the beam width?

~only one wide reflection is seen on the image.

What does the AIUM suggest with clinical safety? (4)

~Do not perform studies without reason ~do not prolong studies without reason ~minimize exposure time (but perform a complete diagnostic exam ~use minimum output power and highest receiver gain required to produce optimal images (ALARA principle)

♥What is the current method for pulsed or CW Doppler?

~Fast Fourier Transform (FFT)

Who regulates system and tx outputs?

~Food and Drug admin (fda)...

What is another word meaning Amplification?

~Gain

HINT: the sonog can adjust depth of view however, the speed of the sound in a medium is a characteristic of the medium and cannot be changed. ♥Therefore, speed is a fundamental limitation of temporal resolution

~HINT...

Units for temp res: Typical value?

~Hertz/ or "per second" ~20Hz-100Hz...

Which fq provides better image detail? High or Low?

~High

♥Line density in a sector image is the number of scan lines per degree of sector. Line density in a rectanular image is the # of scan lines per cm. When the line density is low, temporal res is:

~High

What occurs when there is a High signal to noise ratio? Low signal to noise?

~High signal: high quality image ~Low signal: low quality image

♥Two media have same propagation speed. A has higher density than B..therefore, A's impendence is _____ than B's.

~Higher (same % as the density)

♥Which type of frequency (high or low) sound undergoes more Raleigh Scattering? ♥Example?

~Higher frequency sound. ~red blood cells

♥What are the impendence levels between pzt, gel, skin, and matching layer?

~Highest in PZT>matching layer>gel>skin

♥What have the highest and lowest output intensities?

~Highest: pulsed dopppler ~Lowest: gray scale imaging

♥Explain Rayleigh Scattering:

~If a reflector is much smaller than the wavelength of sound, sound is uniformly distributed in all directions (omnidirectional).

Wavelength influences?

~Image quality (axial resolution)

What are some synonyms for transducer output? ♥Tx output is determined by?

~output gain, acoustic power, pulser power, energy output, transmitter output ♥~by the excitation voltage from the pulser.

What are some examples of recording and archiving devices?

~paper ~magnetic (data can be disrupted by strong magnetic field) ~chemically mediated (disadvantages: contaminated chemicals, wrong temperature)

The diff between the min & max value of an acoustic variable is called:

~peak to peak amplitude

Which tx are the only ones used with spatial compounding?

~phased array tx only, since the sound beams are steered electronically.

Fewer lines = (spatial resolution) Many lines =

~poor spatial resolution ~good spatial resolution

♥What is bernoulli's principle?

~pressure is at its lowest pressure in the middle of the stenosis

♥Creating an image w a 30degree sector requires a certain number of us pulses. Whereas 90degree sector image uses how many times more pulses?

~three times more....

What are some synonyms for compensation? ~can it be adjusted?

~time gain compensation (TGC), depth compensation (DGC), swept gain ~yes it can be adjusted

♥What is directly related to time-of-flight in soft tissue?

~time-of-flight and distance are related

♥What is dynamic receive focusing?

~tiny time delays (phase delays) during reception can be applied to teh elect signals from the tx to the US system. ~Allows for focusing at many depths.

♥SPTA is related to:

~tissue heating

Output power? or Receiver Gain? Which one?

~to determine whether a control affects output power or rec gain, look at its description. ~"outgoing" probably means output power ~"reception or incoming" probably means receiver gain.

What is edge enhancement ideally suited for?

~to distinguish interfaces between structures w different gray-scale characteristics

♥What is the purpose of the gel?

~to further increase the efficiency of sound transmission.

What is the routine periodic evaluation of the US system done for?

~to guarantee optimal image quality...

♥Why are tx designed with backing material?

~to have a few cycles/pulse, so that the numerical LARRD resolution is low and the image accuracy is superior.

What is the purpose of the case?

~to protect the internal components from damage, and insulates the pt from electrical shock.

Why is gel used with ultrasound?

~to remove air from the path of ultrasound

What is coded excitation?

~tradional imaging uses a very short pulse to create each image. ~icoded excitation creates long sound pulses that contain a wide range of frequencies.

For the phased array, the phasing patterns focus & steer the sound beam during:

~transmission

What is the image shape of a vector array?

~trapezoidal, basically a sector with a flat top that does NOT come to a point...

What is eddy currents?

~turbulent flows

♥when a PZT crystal is 1/2 as thick, the sounds fq is:

~twice as high.

What is harmonic frequency?

~twice the transmitted frequency, also called the 2nd harmonic.

Focal depth is determined by: (2)♥

~tx diameter ♥~frequency of the ultrasound

♥Sound beam divergence is determined by 2 factors:

~tx diameter ♥~frequency of the ultrasound

What are the typical values for dynamic range?

~tx dynamic range is the greatest of all systems components, while the recording device has the lower dynamic range.

What is frequency compounding?

~typically, an image is created using the entire reflection of a sound pulse. ~frequency compounding divides the reflection into sub-bands of limited frequency, and an image is created from each of these sub-bands

♥What is dopp phantom used for?

~used to assess the accuracy of pulsed, cont wave & color flow systems...

♥What is the purpose of compensation?

~used to create image of uniform brightness from top to bottom.

♥Small regions of laminar flow will have similar:

~velocities and narrow Doppler spectra.

Frequency shift is always related to:

~velocity

♥Doppler measures ______, not speed:

~velocity

What is the equation for velocity (measured)?

~velocity=true velocity X cos (angle)

What is flow from arms and abdomen into the thorax is called:

~venous return to the heart

Why does respiration have such an effect on the venous system?

~venous system is a low pressure system ~the muscles producing respiration change the pressures in the thorax & the abdomen. ~bl returning from legs flows through 2 closed compartments; the abd & thorax (separated by the diaphragm)

What is coaptation?

~vessel collapse. ~when opposing vessels touch each other. In most cases, venous pressures above the heart are 0mmHg. When b/p is 0mmHg, the vessel collapses (coaptation).

♥What can be used to evaluate doppler systems?

~vibrating string and moving belt phantoms...

Flow:

~volume ~how much? ~volume/time ~liters/min

♥Anemia and dopp?

~we can always successfully perform a dopp exam regardless of the pt's hematocrit.

Transmission with Normal incidence refers to:

~whatever is not transmitted, must be reflected.

What is Doppler Artifact called Ghosting? What is another term for ghosting?

~when low velocity motion from pulsating vessel walls can produce small dopp shifts that bleed into surrounding anatomy. ~color flash...

When are the strongest conclusions made?

~when mechanistic & empirical approaches are in agreement

♥Reflection occurs:

~when propagating sound energy strikes a boundary between 2 media & some returns to the transducer.

♥Posiitive change (shift):

~when source and receiver are approaching each other. ♥~reflected frequency is higher than transmitted

When does diffuse reflection (back scattering) occur?

~when the boundary has irregularites that are approx the same size as the sounds wavelength.

♥Negative change:

~when the source and receiver are moving apart. ~Reflected frequency is less than transmitted frequency.

♥Specular reflection can also occur:

~when the wavelength is much smaller than the irregularities in the boundary.

What is range ambiguity Artifiact caused by?

~when very dep reflections arrive at tx after the next pulse was created ~the system thinks that reflection came from 2nd pulse ~places late-arriving reflection (artifact_ too shallow on the image...

Explain pulse inversion Harmonic imaging:

~where positive & neg pulses are transmitted down each scan line. The - pulse is the inverse of the +, thereby cancelling the fundamental reflections. ~only the harmonic reflections remain and are used to create the image.

♥what type of tx will have aliasing LESS likely to occur?

~with lower fq tx. ~Therefore lower fq tx are desirable for pulsed dopp.

When is MI higher (more likely to produce cavitation?)

~with peak rarefaction pressure & lower frequency sound

Coefficients are reported____ units, as ____

~without units, as percentages.

♥What axis are used for A-Mode?

~x & Y axis

Can output be adjusted?

~yes ~effects the strength of every pulse transmitted to the body ♥~The brightness of the image changes

What is hydrostatic pressure in a supine patient?

~zero at all locations

♥Relationship of imaging depth and PR?

~♥ Directly related. (as one increases, so does the other.

♥What is the purpose of rejection?

~♥ Reject eliminates low-level noise in our images. ~displays low level echoes only when they are clinically meaningful.

♥What is the major disadvantage of pulse inversion imaging?

~♥the frame rate is 1/2 that of the fundamental imaging. ~pulsed inversion imaging degrades temporal res while improving spatial resolution (image detail)

♥♥What is preprocessing?

~♥♥Manipulating the data before storage in the scan converter. ~Once pre-processing occurs, the data is altered forever! It cannot be reversed!

♥Will transmission & Reflection w/ Oblique Incidence occur??

♥ I don't know!!!

♥In soft tissue, sound w a freq of 2MHz has a wavelength of:

♥.77mm (1.54mm/ 2MHz = .77mm)

♥In soft tissue, sound freq of 1MHz has a wavelength of :

♥1.54mm

♥What is 0.000001 =

♥10(-6)

♥What can an ellipse be used to measure?

♥Area

♥What term is the same as stiffness? Relationship to speed?

♥Bulk modulus. ~When bulk modulus increases, speed increases

♥Stiffness is related to:

♥Change in shape (squishability)

♥What 2 terms are the opposite of stiffness

♥Compressibility & Elasticity

♥Decrease by a factor of _____ means:

♥Divide by that number

♥Increase by a factor of______ means:

♥Multiply by that number

♥NOTE: by itself, increasing overall gain cannot create an image w uniform brightness. Also the signal to noise ratio is unchanged when amplification levels change.

♥NOTE

♥Density & speed travel:

♥Opposite directions

♥Stiffness and Speed travel:

♥Same direction

♥Defn of pulse duration: Units: Determined by: change???

♥The time from the start of a pulse to the end of that pulse, the actual time that the pulse is "on". ~ųs, or any unit of time ~sound source ~Cannot be changed

What is the meaning, prefix, and symbol of: ♥a. 10(9) ♥b. 10(-6)

♥a. billion, giga, G ♥b. millionth, micro, ų

♥Constructive Interference: Also called♥

♥combined wave is greater than the original 2 waves ♥In-phase waves

♥In diagnostic imaging, pulsed sound is used to:

♥create anatomic images.

♥What is the general rule with the avg speed of different mediums?

♥gas<lung (air) <fat <soft tissue<bone<solid ♥Gas is slower while solid is faster

♥Destructive Interference: ♥Also called

♥the new wave is less than one of the original waves ♥Out-of-phase

♥Defn of pulse repetition period It includes: Units: Determined by: change??

♥the time from the start of one pulse to the start of the next pulse. ~one pulse duration & one "listening time" ~any unit of time ~sound source ~CAN change

♥Density is related to:

♥weight

♥What are the typical values with clinical imaging for PRF?

♥~1,000-10,000Hz (1-10kHz)

♥Define of Audible Sound (frequency)

♥~20Hz - 20,000Hz.

♥What is the typical range for frequency?

♥~2MHz to 15MHz

What is the speed of the following? (m/s): ♥Air Lung Fat Soft Tissue ♥Tendon ♥Bone

♥~330m/s ~300-1,200m/s ~1450m/s ~1540m/s ♥~about 1,850m/s ♥~2,000-4,000m/s

♥If amplitude is doubled, the power is increased by a factor of:

♥~4 (2x2=4)

♥Define Ultrasound (frequency)

♥~A wave with a frequency exceeding 20,000Hz (20kHz). ~This frequency is so high that it cannot be heard by man.

♥What is the highest to lowest attentuation media?

♥~Air> bone & lung> Soft tissue > Water

♥SPL determines..

♥~Axial resolution (image quality)

♥What is the relationship between speed and wavelength?

♥~Directly related (slow medium=short wavelength...fast medium=long wavelength).

♥As imaging depth increases, period:

♥~Increases

♥Define of Intensity Equation ♥Units

♥~Intensity is the concentration of power in a beam. ~Intensity (w/cm2)=Power/beam power ~♥ W/cm2

♥Define of a transverse wave

♥~Particles moving in a perpendicular direction (right angles or 90degrees) to the direction of the wave.

♥Define of a longitudinal wave

♥~Particles moving in the same direction as the wave

♥Unit for pressure?

♥~Pascals (Pa)

♥Amplitude units of the acoustic variables:

♥~Pressure (Pa) ♥~Density (grams/cubic cm) ♥~Particle motion (cm, in, units of distance)

♥The best studies are:

♥~Prospective & Randomized

♥What is the relationship betw PRP & PRF?

♥~Reciprocal / Inversely related.

♥What is the relationship between frequency and Period?

♥~Reciprocal/ or inversely related ♥~when one goes UP the other goes DOWN

What are the 2 decibel scales?

♥~Relative scale-ratio of the final to the initial strengths. ~A comparison of 2 intensities

♥Which resulting intensity description is the most important for thermal bioeffects?

♥~SPTA

♥What does it mean if the duty factor is 100% (1.0)??

♥~System is producing continuous sound....Continuous wave.

♥Define Duty Factor Units Determined by: Change?? ♥Typical values

♥~The percentage or fraction of time that the system transmits sound. ~No units ~Sound source ♥~0.1%- 1% (.001 to .01)..lots of listening & talking

♥Unit for Power:

♥~Watts

♥What is the typical values of pulse duration in clinical imaging?

♥~a pulse is comprised of 2-4 cycles.

♥What are rarefactions? (2)

♥~areas of decreased pressure & density ♥~regions of lower density & pressure

♥What are compressions? (2)

♥~areas of increased pressure & density ♥~ares of higher density and pressure

♥What are the units of relative amplitude?

♥~dB

♥Amplitude may be expressed in:

♥~decibels (dB).

♥As imaging depth decreases, Pulse repitiion period:

♥~decreases

♥When frequency INCREASES, period... ♥when frequency decreases, period....

♥~decreases ♥~increases

♥As imaging depth increases, PRF....

♥~decreases (inverse relationship)

♥PRP is determined by:

♥~depth of view

♥With a mech tx, what happens if the crystals are defective?

♥~destroys entire image....

♥What is the formula for pressure?

♥~force/area

♥PRF is determined ONLY by depth of view and NOT related to:

♥~frequency

♥Higher frequency waves have ___________ wavelength. While lower freq. waves have a ___ wavelength.

♥~higher= shorter wavelengths ♥~lower = longer wavelengths

♥Frequency affects what?

♥~image quality (penetration and axial resolution).

♥What type of wave is sound? (2)

♥~mechanical and longitudinal

♥Relationship betw power & amplitude

♥~power is proportional to the waves amplitude squared. (power œ (Amplitude)2

♥Relationship of intensity to the amplitude of the wave

♥~proportional to the amplitude of the wave squared ☺Amplitude squared

♥Define Infrasound

♥~sound with frequency below 20Hz. ~too low to be heard by man

♥If the duty factor is 0?

♥~system is off.

♥Amplitude is not:

♥~the difference between the MINIMUM & MAX values of an acoustic variable.

♥Define wavelength; Units: Determined by: Change???

♥~the length or distance of a single cycle. ~mm or any unit of length ~both the source and the medium ~CANNOT be changed by sonographer

♥Define PRF(pulse repetition Frequency) Units Determined by Change??

♥~the number of pulses that occur in one second ~Hertz, Hz, per second ~Sound source ~CAN change

♥Sound must travel:

♥~through a medium

♥Equation for Wavelength:

♥~wavelength(mm) = propagation speed(mm/us)/frequency (MHz) or... ~L or λ = C/F

♥♥What is the avg speed of all sound (regardless of frequency in biological tissue?

♥♥1.54km/s= 1,540m/s = 1.54mm/ųs

♥♥Terms that have the same meaning: Shallow imaging....(3)

♥♥High pulse repetition frequency High duty facor SHORT pulse rep period

♥♥Terms that have the same meaning: Deep imaging.....(3)

♥♥Low pulse rep freq (PRF) ♥♥Low duty factor ♥♥High pulse rep period

♥♥Describe analog-digital conversion (A-D)converter

♥♥electrical signals created by the pzt are analog. ~but a digital scan converter can only process computer information. ~the analog signal must be converted into digital form for input into the scan converter

♥♥What is log compression?

♥♥related to the ability of humans to see the gray scale differences in anatomic structures. ~Lowers the high level ehoes and boosts the low level echoes. ~The image data's dynamic range is reduced. ~It is controlled by the sonographer

♥♥Equation for Doppler shift:

♥♥~Doppler shift= 2 X reflector speedX incident frequency X cos (angle)/ propagation speed

♥♥What is post processing?

♥♥~Manipulating the data after it has been stored in the scan converter memory but prior to display. ~Increases versatility of the display process. ~This can be undone ~♥performed on frozen images

What happens with hydrostatic pressure below heart? Above heart?

~pressure measured is greater than circulatory pressure b/c hydrostatic pressure is positive. ~Above: presure measured is less than circ pressure b/c hydrostatic pressure is negative.

Equation for hydrostatic pressure?

~pressure measured=circulatory pressure + hydrostatic pressure

♥What are the goals of the periodic eval?

~proper equip operation ~detect gradual changes ~minimize downtime ~reduce number of repeat scans...

What is the role fof color flow dopp?

~provides 2d flow info directily on anatomic image. ~size of color jet is most affected by color dopp gain settings. ~poorer temp resolution b/c of multiple packets. ~pulsed us, subject to range res & aliasing

What is temporal compounding (persistence)?

~provides a history of past frames that is added to the current frame. ~the avg of previous frames to create the displayed image ~consolidates past frames ~displays a smoother image and reduces noise ~useful for stationary or slow-moving structures

♥What does the multi focusing ability w annular phased array tx provide?

~provides electronic focusing in all planes at all depths; a core sample. ~this provides optimal lateral resolution at all depths throughout the image.

Inertial loss results from:

~pulsatile flow, both acceleration & deceleration ~velocity changes at a stenosis

What are the 5 parameters of the Pulsed Wave?

~pulse duration ~prp ~prf ~spatial pulse length ~Duty factor

♥PZT crystals vibrates with a magnitude related to?

~pulser voltage

♥What is the purpose of smoothing?

~putting an envelope around the "bumps" to even them out.

♥What is the active element in the tx?

~pzt crystal aka..../ceramic/PZT/crystal

Explain how convex or curved arrays are arranged:

~pzt cyrstals arranged in a curve to provide a natural sector image ~may be sequential or phased array...

♥What are the 3 factors that determine Resistance?

~radius of lumen (most important) ~length (larger, higher resistance) ~viscosity of fluid (thicker fluid=greater resistance)

♥color dopp is pulsed us technique & is subject to: (2)

~range resolution or specificity ~aliasing

♥What is analog?

~real world: a variable attains a continuum of values. Such as: ~actual weight of an individual & true length of a piece of string.

♥What is the image shape of the linear switched array?

~rectangle image shape, NO WIDER than the tx.

Function of a Pulser?

~recvs timing signal from the synchronizer. ~creates an elec signal that excites the pzt crystal

♥♥Doppler shift is directly related to the:(3)

~red blood cell speed ~fq of the transducer ~cosine of the angle between flow and the sound beam

If image is too bright, first....

~reduce output power

Speckle reduces: and negatively impacts?

~reduces image contrast and spatial resolution ~may negatively impact the diagnostic accuracy of our images.

♥Anemia has what effect on viscosity?

~reduces viscosity b/c the blood is thinner

♥Defn Compression:

~reducing the total range of signals, from the smallest to the largest

Spatial refers to:

~referring to distance or space

Describe turbulent flow:

~refers to the chaotic flow that goes in many different directions and speeds. ~Flow varies from instant to instant & from location to location ~streamlines are obliterated

Equation for Incident Intensity:

~reflected Intensity + Transmitted Intensity

What is partial volume artifact/ or section thickness artifact?

~reflections produced by structures above or below the ideal imaging plane appear in the image...

♥Explain edge shadow/refraction

~refraction at the edge of a circular structure can also create an artifact. This is called shadowing by refraction or edge shadow. ~Due to refraction & beam spreading...

♥Brightness is related to:

~related to the brilliance of the displayed signal

Defn epidemiological study:

~require large numbers of patients when the occurrence rate of the measure effect is small.

What occurs at shallow depth with listening time? " """""""" at greater depth with listening time?

~requires less listening time ~greater requires longer listening time...

♥in the far field , beam is narrow & resolution is ____ with large diameter, _____ fq sound.

~resolution is best ~high frequency sound

What causes viscosity?

~results from a fluid sticking to itself, internal friction.

♥What is B-Mode? Explain the process of B-Mode

~returning echoes are presented as spots on the line of travel of the emitted US pulse. The stronger the returning echo, the brighter the spot. ♥The brightness of the dot is porportional to the amplitude of the returning echo.

♥Material is bonded to the active element of the tx in order to reduce ____

~ringing

What is the crystal make-up and shape of the mechanical scanner?

~scan head contains one disc-shaped, element (like a coin)

♥What is spatial compounding?

~scan lines are streered by the tx in different directions or views, so structures are interrogated by multiple pulses from several different angles.

♥What is the strategy of the annular phased array tx?

~selected focal zones, use inner crystals for shallow regions and outer crystals for deep regions.

What is the purpose of a wall filter?

~serve as a reject for dopp. ~wall filters exclude low level dopp shifts around the baseline, while having no effect on large dopp fq shifts ~Wall filters are used to reject "clutter"...

In regards to max imaging depth, what will create a frame in less time? Why?

~shallow depth of view makes a frame faster, and improves temp res...

What are the effects of stable cavitation?

~shear stresses & microstreaming in surrounding fluid

Pulser mode in pulsed wave, single crystal tx?

~short duration electrical "spike", one electrical spike per ultrasound pulse

♥"short pulse" means a short _____ ____ ____, or a short _____ ______

~short spatial pulse length ~or a short pulse duration

♥What kind of pulses create better LARRD resolution?

~shorter

♥Highest frequency =

~shorter pulse, with fewer cycles.

Multi-directional array have more elements in which direction?

~side to side than with up & down...

Why do echoes returning from greater depths have lower amplitudes than those returning from shallow depths?

~since deeper pulses undergo more attenuation

What type of tx is always fixed focus?

~single crystal tx

♥What type of focus does the annular phased array tx have?

~smal diameter rings have a shallow focus but diverge rapidly. ~large diameter rings have a deep focal length.

Shallow focus=

~small diameter ~low frequency

What is the shape & make up of the annular phased array tx?

~small number of ring-shaped (like a donut) elements

♥What is Doppler spectral broadening?

~small regions of turbulent flow having vastly different velocities

♥What is the relationship betw sample volume size & dopp spectrum?

~smaller sample volumes create doppler spectra w larger, cleaner envelope ~larger sample volumes create dopp spectra w smaller envelopes (spectral broadening)

Why does refraction artifact occur?

~sound changes direction striking a boundary: obliquely when the media have different propagation speeds...

What is mirror image?

~sound may bounce off of a strong reflector, called a mirror. ♥~US systems assume that sound travels directly to a reflector and back to the transducer...

Frequency is determined by: Can it be changed?

~sound source ~Cannot be changed

♥What determines the resonant freqency of a tx...with continuous wave tx?

~sound waves fq = the frequency of the voltage applied to the pzt by the machines electronics.

What is flow energy is lost, converted to?

~sound-murmurs, bruits ~vibration-thrill (these are palpable)

The more pixels per inch (pixel density), the greater the detail in the image. This detail is called:

~spatial or detail resolution

♥Low line density images use fewer pulses, and have better temp reso. However, lower line denisty degrades: Also called

~spatial resolution ~also called detail resolution...

♥Increasing the line denisty degrades temp reso but improves:

~spatial resolution...

What is cross talk?

~special form of mirror image where the dopp spectrum appears above and bleow the baseline. ~aka Doppler Mirror on vasc exam...

Velocity:

~speed ~how fast? ~distance/time ~meters/sec

♥♥Doppler shift is inversely related to the:

~speed of sound in the medium

Explain what happens as sound travels regarding the beam width changes:

~starts out exactly the same size as the tx diameter (aperture), gets progressively narrower until it reaches its smallest diameter, and then it diverges.

♥A group of bits is assigned to each pixel to:

~store the gray scale color assigned to that pixel.

What are some synonyms for rejection?

~suppression, threshold

Where does coded excitation take place? Increases? Improves?

~takes place in the pulser ~increases signal-to-noise ratio ~improves penetration and axial, spatial, and contrast resolution

Unfocused beams are more likely to cause (temp)?

~temp elevation in tissues

♥Focused beams are less likely to cause (temp)?

~temp elevation in tissues

♥What happens when there are pulses of sound at higher fq ?

~tend to diverge less in the far field.

♥What are the methods for period eval?

~test under known, defined conditions ~constant instrument settings ~use phantom with measureable characteristics ~image in identical environment...

♥What does dead zone measure? How is it fixed?

~tests teh depth where uniform tissue~ like textures appear... ~Remedied by stand off pad

Defn of temporal resolution

~the ability to accurately locate moving structures at any particular instant in time... ~♥"How good is my movie"

♥What is mimimum sensitivity performance measure?

~the ability to detect low level echoes in the far field. ~it is the first echoe to appear...

Defn axial resolution: Units:

~the ability to distinguish 2 structures that are close to each other front to back, parellel to, or along the beams main axis. ~all distance units

What is the defn of resolution?

~the ability to image accurately (not merely the quality)

♥Defn of attenuation coefficient Units Change?

~the amount of attenuation per centimeter. A way to report attenuation without dealing with distance. ♥~dB/cm ~Attenuation coeff doe NOT change when path length changes.

What does an acoustic footprint describe?

~the area of contact between the tx and the skin...

♥Explain Doppler shift (or Doppler Frequency)

~the change or variation in the frequency of sound as a result of motion between the sound source and the receiver. ~the greater the velocities, the greater the doppler shift

♥Defn of sterilization

~the complete destruction of all living microorganisms by means of exposure to heat, chemical agents, or radiation.

♥The agnitude of shift depends upon?

~the cosine of the angle between the sound beam and the direction of motion.

Defn of attenuation: ♥Units

~the decrease in intensity, power & amplitude of a sound wave as it travels. ~dB (negative, since attenuation causes intensity to decrease).

Define of amplitude: Determined by: Change???

~the difference between the avg value & the maximum value of an acoustic variable ~sound source (initially) ~Yes

♥When time-of-flight is known , we can determine:

~the distance

♥Example that fill in interpolation is used?

~the edges of a circular structure will be better defined

What is fundamental frequency?

~the freqency of the transmitted sound wave.

♥What is normal sensitivity perf measurement?

~the gainsetting where all of the pins in the aium test object are displayed on the CRT (all echoes appear)... ~all other performance measurements are made at this setting

When reflected and transmitted intensities are added, the result is:

~the incident intensity

What is the focus/or focal point?

~the location where the beam reaches its minimum diameter.

Peak is:

~the maximum value

Average refers to:

~the mean value

Defn lateral resolution: Units:

~the minimum distance that 2 structures are separated by side-to-side or perpendicular to the sound beam that produces two distinct echoes. ~all units of length

Defn of flow?

~the movement of a fluid from one location to another

♥What else is spatial res related to?

~the number of lines per frame.

♥What is digital data?

~the numbers from the digital scan converter can be processed and then re-translated for display as an image.

♥What is spatial resolution on a digital display determined by?

~the pixel density

Defn of reflected intensity:

~the portion of the indienct intensity that after striking a boundary, changes direction & returns back from where it came.

♥What does a hydrophone measure?

~the pressure in a sound beam...

♥What is the defn of real time imagin?

~the production of a motion picture ~a series of frames displayed in a rapid fashion to give the impression of constant motion...

♥contrast is determines: What level of contrast are bistable images?

~the range of brilliancies that are displayed. ~bistable images are high contrast

♥defn of bandwidth: Units of :

~the range of frequencies between the highest & the lowest frequency emitted from the tx. ~Hz

Define of propagation speed: Units: Determined by: Change?

~the rate that sound travels through a medium. (aka velocity or speed. ~meters per second, mm/ųs ~medium ONLY- density and stiffness ~CANNOT change

♥What is dynamic range:

~the ratio of the largest to the smallest signal strength that each component processes. ~it is the ratio of two numbers

♥How is lateral resolution at all depths optimized?

~the receive beam becomes as narrow as possible at all depths...

♥What happens when the speed is less than soft tissue?

~the reflector will be placed too deep on the display....

♥What happens when prop speed is greater than 1,540m/s?

~the reflector will be placed too shallow on the display...

♥What is the Fraunhofer zone?

~the region or zone deeper than the focus, beyond the near field.

♥What is Fresnel Zone?

~the region or zone in betw the tx and the focus (near zone)

Where is the focal zone?

~the region surrounding the focus where the beam is "sort of narrow" and the picture is relatively good.

♥What is Dosimetry?

~the science of id'ing & measuring those characteriscs of an us field which are especially relevant to its potential for producing bio effects...

Period is determined by: Can it be changed?

~the sound source. ~Cannot be changed

♥What makes the annular phased array tx different from other phased array tx?

~the steering is performed mechanically.

♥Defn time-of-flight

~the time needed for a pulse to travel to and from the tx and the reflector

Define of period/time

~the time required to complete a single cycle ~aka...the time from the start of a cycle to the start of the next cycle...

Defn of Tf: What is relationship betw Tf and frame rate?

~the time required to make a frame ~Tf and FR are reciprocals (when frame is made quick, many frames are created each second)...

♥Pulse duration is a characteristic of ??

~the transducer. ♥♥A pulse is a pulse is a pulse.

♥What happens at standard intensities

~there are no known cases of bioeffects or tissue injury in diagnostic imaging...

♥Describe steering in a switched array..

~there is no steering, pulses are sent down parallel lines. ~the lines are parallel and are equally spaced.

♥What happens to the sound beam in the far zone?

~they diverge

According to Huygens Principle, what happens when multiple wavelets are combined?

~they produce an hourglass-shaped main sound beam.

♥Lower fq=

~thick crystal ~slow PZT

♥What determines the resonant fq of a pulsed tx?

~thickness ~propagation speed of the pzt material

Frequency (Pulsed) is determined by:

~thickness of ceramic & speed of sound in ceramic

♥Higher fq=

~thin crystal ~fast PZT

♥What is thermal index?

!~ # proposed by AIUM that relates to tissue heating. ~It is the calculation related to the possible temp elevation, measured in degrees centrigrade, that could or may be produced by the sound beam

HINT: Spectral dopp (pulsed & cw) measures peak velocity. Color flow measures mean velocity

...

NOTE: a thermal index of 2 means that a temp elevation of 2 degrees centigrade MAY occur. Exposure may be reaching the upper limits.

...

♥Multidimensional Arrays: 2d create 3d or 4d images: 3d measures...

...~ volumes (such as with a cyst) more accurately that 2d, a-, b-, or m-modes.

♥As the returning sound beam strikes the tx, the size of the tx surface listening for echoes varies; how is this accomplished?

.~varying the number of elements used to recv the reflected signal...

♥Hint: the number of gray shades displayed by "n" bits is 2n

Hint

A-♥Define of an acoustic propagation property B-Define Biological Effects:

A-The effects of the medium upon the sound wave. B♥~The effects of the sound wave upon the biological tissue.

NOTE: compensation makes an image equally bright at all depths. Ask the question "is the image of uniform brightness from the top to bottom?"

NOTE

HINT: Be on the lookout for questions that ask "what will you adjust if you cannot see reflectors in the near field on your image?"

HINT~TGC

HINT: Increasing tx output improves signal-to-noise ratio. The meaningful signal strength is increased while the noise level remains unchanged.

HINT

HINT: Turbulence may be identified as spectral broadening.

HINT

HINT: Use of CW means no damping, narrow bandwidth & hi-Q. Advantages are higher sensitivity and ease in detecting small doppler shifts.

HINT

HINT: flow in lower extremeities moves with the diaphragm. The opposite flow changes occur with venous return to the heart.

HINT

HINT: if emitted frequency is FE and reflected frequency is FR, then Doppler frequency (FD)=FR-FE

HINT

HINT: look for words "grainy, granular, & interference effects". You will not be asked to identify speckle on an image.

HINT

HINT:Pulse inversion harmonics uses wide-bandwidth, or broadband tx.

HINT

♥HINT: Doppler shift=received frequency-transmitted frequency

HINT

♥♥HINT: In order to accurately determine velocity, the angle between the directions of flow & sound beam must be known.

HINT

HINT: If you have an issue with mathematics, multiply each of the possible answers with the number that is given in the question stem. The correct answer is the one that provides the value 1.0...

HINT...

HINT: refraction artifact degrades lateral resolution. Cannot id refraction artifact from true anatomy with a single static image.

HINT...

HINT: true unidirectional flow appears bidirectional. Turn down the pulse wave dopp gain and use a new window. The original window is too close to 90degrees.

HINT...

♥HINT: Generally linear array tx have poor elevaional resolution.

HINT...

♥HINT: LObe artifact degrade lateral resolution. ~Cannot identify lobe artifact from true anatomy with a single static image.

HINT...

♥HINT: Sensitivity: when adj make changes in display or echo brighness from scarcely visible to fully saturated, sensitivity is being assessed.

HINT...

♥HINT: look for "interference effcts, grainy appearance....you will not be asked to identify speckle on an image..

HINT...

♥HINT: with lobe artifact, the assumption that reflections arise from the beams main axis is violated.

HINT...

♥♥HINT: What does the 2 in the doppler equation represent?

HINT: Answer....In clinical dopp, there is a double doppler shift. The 1st occurs when the sound strikes the cell. The 2nd shift results from the moving blood cell reflecting the wave back to the tx.

HINT: With compression, decibels add or subtract. RULE: Subtract compression dB's from beginning dynamic range dB's to get compressed signal's dynamic range dB.

HINT: compression

♥LARRD equation for soft tissue?

LARRD resolution (mm)= .77 X #cycles in pulse/frequency(MHz)

What are the units associated with the following: Length Area ♥Volume

Length~cm, feet Area~cm2, ft2 Volume~♥cm3, ft3

NOTE: under controlled conditions, bioeffects are considered beneficial. Low level US intensities-no known effects

Note: bioeffects

Remember: Bi-directional dopp uses phase quadrature processing.

Remember: ,,,,

Compensation treats echoes differently, depending upon:

The depth at which they arise

♥HINT: a phantom is an objective standard. Medical/Legal: a must for every laboratory An US system is only as strong as its weakest component

hint...

♥# of crystals in pulsed wave dopp? Advantage of?

~One crystal, alternates between sending and receiving. ~Advantage: echoes arise only from the area of interrogation, the sample value or gate. We can adjust the receive gate (this is called range resolution or range specificity or freedom from range ambiguity artifact).

Pulse refers to:

~Only to the time the pulse exists (transmit only)

♥What is the mnemonic for Normal incidence?

~P erpendicular ~O rthogonal ~R ight angle ~N inety degrees

By adjusting the imaging depth, the operator changes the: (3)

~PRP, PRF, and duty factor

Which tx have a better lateral res b/c the focal depth is adjustable by the sonog?

~Phased array

♥What does PACS stand for?

~Picture archiving and communications system

What does the AIUM say regarding clinical safety?

~Potential benefits should outweigh the risks.

What are the 3 acoustic variables?

~Pressure ~Density ~Distance

What are the 2 steps for demodulation?

~Rectification ~Smoothing (or enveloping)

♥What is x-axis? Measured by?

~Reflector depth ~measured by pulse's time-of-flight

What is M-mode related to? NOT related to?

~Related to location ~Not related to echo amplitude.

What is inertia?

~Relates to the tendency of a fluid to resist changes in its velocity.

What are the 6 resulting Intensity descriptions?

~SAPA ~SATA ~SATP ~SPPA ♥~SPTA ~SPTP

♥What does bioeffects intensity limit?

~SPTA : 100mW/cm2 unfocused : 1W/cm2 or 1,000mW/cm2 focused...

♥What is duplex ultrasound?

~Simultaneously imaging & doppler.

♥What is longitudinal resolution?

~Smallest distance where two pins are displayed as two echoes the longitudinal resolution (front to back or parallel to sound beam)...

What are the five key words for Intensity?

~Spatial ~Temporal ~Average ~Peak ~Pulse

2D arrays have the same number of elements in the up & down and side-to-side directions.

~Statement

What are: TIS TIB TIC

~TI in soft tissue ~TI in bone ~TI cranial bone is at or near the skins surface

Equation for Tf?

~Tf X FR=1...

What is the steering of a mechanical tx?

~The active element is moved by a motor, oscillating crystal or mirror through a pathway, automatically creating a scan plan.

Role of the pulser?

~The component that controls the elec signals sent to the tx for sound pulse generation. ~determines the PRF, pulse amplitude, & pulse rep period ~♥ Creates teh firing pattern for phased array systems (called beam former)...

Define of Intensity: ♥Equation: changed??

~The concentration of energy in a sound beam. ♥~Intensity (watts/cm2)= power (watts)/beam area (cm2) ~CAN be changed

Role of the display

~The device assoc w the presentation of processed data for interpretation...

In regards to pressure: what happens with expiration?

~The diaphragm ascends into the thorax ~pressure within the abd cavity decreases; venous flow in legs increases ~pressure within the throax increases; enous return to heart decreases.

What is Nyquist frequency? Nyquist equation

~The dopp fq at which aliasing occurs, equal to 1/2 the PRF. ~Nyquist limit(kHz)=PRF 1/2

♥Role of the receiver:

~The electonic assoc w processing the elect signal produced by the tx during reception & producing a pic on an appropriate display...

What happens with frame rate if the depth of view is doubled?

~The frame rate will be halved...

Defn of incident intensity:

~The intensity of the sound wave at the instant prior to striking a boundary

Define Spatial PUlse length: Units Determined by Change?

~The length or distance that an entire pulse occupies in space. (start to end of ONE pulse) ~Any unit of distance ~Both source and the medium.

What is registration accuracy?

~The machines ability to place echoes in proper positions while imaging from diff orientations...

Define Intensity Reflection Coefficient (IRC)

~The percentage of the US intensity that bounces back when the sound strikes a boundary.

Defn Intensity Transmission Coefficient (ITC)

~The percentage of the US intensity that is allowed to pass through when the beam reaches a boundary between two media.

Defn of transmitted Intensity:

~The portion of the incident intensity that, after striking a boundary, continues on in the same general direction that it was originally traveling.

Explain Demodulation:

~The process of extracting the Doppler fq (which is low) from the tx fq (which is high) is called demodulation.

Define of Power: Determined by: Can it be changed?

~The rate that work is performed, or the rate of energy transfer. ~Sound source (initially) ~Yes

What is the overall function of the receiver?

~The receiver can boost the strength of signals, process them and prepares them for display.

What is non-linear behavior?

~The small difference in speeds, which distorts the sound wave and creates harmonics. ~sound moves slighlty faster in regions of compression (higher pressure). ~sound travels slightly slower in regions of rarefactions (lower pressure).

♥What is Huygens Principle?

~This explains the hourglass shape of an imaging tx sound beam

♥What is a stenosis? ♥What can a stenosis cause?

~a narrowing or irregularity in a lumen ~Cause: changes of flow direction increased velocity in the stenosis, highest velocity at the pt of max narrowing turbulence at exit pressure gradient across the stenosis arterial flow loses its pulsatile nature & becomes more continuous

Defn logarithm: Ex.. Hint of logarithms:

~a novel way of rating numbers. It represents the number of "10's" that are multiplied together to create the original number. ~Log of 100...10x10=2 ~Count the zero's...

What is the mechanical index? ♥Equation for MI?

~a number proposed in the AIUM guidelines that relates to cavitation. ♥~MI=Peak rarefaction Pressure/√frequency

♥Defn of elements

~a single slab of PZT cut into separate pieces called elements...

What is a thermocouple

~a small device embedded in absorbing material. ~the us energy is converted into heat, the it measures the temp change. ~specific locations are measureed with the thermocouple...

What is Vortex?

~a swirling pattern of rotational flow

What is a calorimeter?

~a tx which turns acoustic energy into heat ~total power of the US beam can be calculated...

♥Defn of quality factor:

~a unitless number representing the extent of damping.

♥What is the advantage of cont wave dopp?

~able to measure very high velocities accurately.

What are the 3 components of attenuation?

~absorbtion (primary, sound converted into heat) ~scattering ~reflection

What is the role for pulsed wave dopp?

~accurately identifies the location of flow (range resolution) ~has good temporal res. Range resolution, aliasing.

♥Reflection of an ultrasound wave depends upon___ of the media on either side of the boundary.

~acoustic impendences

As a general rule, there are only 2 mathematical operations that are done with dB's....they are:

~addition and subtraction.

♥What are five ways to eliminate aliasing?

~adjust the scale (this increases PRF & Nyquist) ~select new view w a shallower sample volume (this increases the PRF) ~select a tx w a lower fq (reducs the dopp shift for given velocity) ~use cont wave dopp (no aliasing with CW) ~baseline shift (this is for appearance only)

♥What is the meaning of phased array?

~adjustable focus or multi-focus; achieved electronically

What effects do receiver gain have on image?

~affects the brightness by changing the amplification of the elct signals after returning to the receiver. ~when amplification is increased, the elect signals in the recv are boosted, and the image will be brighter.

What is the disadvantage of pulsed wave dopp?

~aliasing, errors in measuring high velocities

What is the role for power mode dopp?

~allows the use of color when with low velocity or small volumes of blood flow. ~greatest sensitivity

♥What is the preamplifier?

~alters the signal before it is amplified, often performed in the probe.

♥What are shades of gray on doppler spectrum related to? (2)

~amplitude of the reflected signal or ~number of red blood cells creating the reflection

♥Doppler measures frequency shift NOT:

~amplitude.

What is elastography?

~an emerging technology ~a dynamic technique that produces images, called elastograms, based on the deformation when a force is applied to a tissue. ~identifies tissues of different stiffness

♥With Huygens Principle what is each tiny part of the large tx face considered?

~an individual sound source.

♥What are obtuse angles?

~angles greater than 90degrees and are oblque

♥What is an acute angle?

~angles less than 90degrees, and are oblique.

Role of storage

~any number of devices and media used to permanantly archive the US data....

Defn of transducer:

~anything device that converts one form of energy to another.

Describe a comet tail

~appears as a solid line directed downward, merged reverberation ~signle, solid, hyperechoic line, parellel to the sound beam

When does aliasing appear? How can you eliminate?

~appears when the dopp shift exeeds the nyquist limit ~elimatd when the dopp spectrum shrinks...or the nyquist limit is raised

♥Defn of disinfection:

~application of a chemical agent to reduce or eliminate infectious organisms on an object.

Crystal #, and shape of phased array tx?

~approx 200 rectangle shaped elements arranged in a line.

What is the crystals, # and shape of convex/curved array?

~approx 200 rectangular shaped elements ~image shape is a blunted sector, fanned shaped image...

What is the value of attenuation coefficient in soft tissue? Math expression meaning 1/2 frequency..

~approximately 1/2 of the frequency (MHz) ~0.5dB/cm/MHz

Explain side lobes:

~are mechanical ~single crystal tx create side lobes ~side lobes are second copies, but the artifact appears side by side to the true anatomy...

Explain grating lobes:

~arrays create grating lobes ~are fixed when elements are subdivided and excited by different electrical volatages apodization....

Facts regarding of pulsatile flow?

~arterial, cardiac contraction, high rate, higher pressure