SPI study guide
cardiac pulsatility
"ripples" of motion caused by adjacent cardiac contraction causes turbulent flow in upper vena cava, upper arms, & hepatic veins abnormal if seen in lower extremeties = congestive heart failure
dynamic range
# of shades of black, white and grey displayed on image
Reynold's number
-# expressing balance of inertial & viscous forces acting on the blood flowing - avg flow x density x pressure -Color Doppler turbulence - <1500 laminar flow ->2000 turbulence
phantom testing
-a phantom is used as the standard for testing Us system -required for system calibration and to statisfy medical/legal needs
color gain
-adjust displayed amplitude of reflected freq shift from flowing blood -increasing overall gain increases the strength of all reflected signlas, regardless of reflector depth -determines where color is displayed on image related to threshold -overgaining can lead to noise artifact (clutter/flash)
sample volume width
-adjusts amount of flow evaluated in a specific location -smaller sample sizes produce more accurate color Doppler information w/ faster frame rate & improved temp resolution
Power Doppler Imaging
-aka color angio or color Doppler energy mode -measures energy variance NOT freq shift -displays an approx of lower echo amplitudes -more sensitive -NOT angle dependent -determines presence or absence of flow
color packet size
-also called ensemble length -refers to # of samples taken during evaluation -# of pulses per scan line for color Doppler -# pulses per scan line increases, color packet size incrases to provide improved sensitivity
PW doppler hints
-always use <60 angle on cursor w/ arterial exams -adjust scale, baseline, and gain -smaller sample sizes give accurate waveforms - cursor angle must be parallel to flow
posterior enhancement
-anechoic structures allow sound to be transmitted through and there is increased reflection from structures posteriorly -occurs posterior to structures w/ low attenuation -can be beneficial to evaluation & diagnosis -spatial compounding & multiple focal zones can reduce appearance of posterior enhancement
direction of flow
-angle less than 90- positive shift -angle greater than 90- negative shift -assess the steering angle & match the postive and negative shifts to colors on color bar
autocorrelation
-automatically correlates data from multiple sampling sites -process is slightly less accurate than the fast fourier transformer (FFT) but FFT is not fast enough to perform this function -assesses the data from multiple sampling sites & produces display representing mean flow velocities requires at least 3 pulses per scan line to process & display color -displays average Doppler shift frequencies -calculates mean flow velocity
spectrum analyzer
-contained within Doppler system -produces graphic displays -blood velocity is calculated, NOT measured -determines peak & mean Doppler shift frequencies -uses FFT to process data & provide it graphic display -FFT requires a min of 2 samples per cycle to produce Doppler tracing
mirror imaging
-created as sound reflects off of a strong reflector -appears as second copy of structure deeper on the image
beam width artifact
-doppler sample volume collects data at a specific location and across width of beam in that location -wider sample volumes can detect two different flow patterns simutaneously
Color Doppler
-duplex imaging refers to combining 2D imaging w/ Doppler technique (color, PW, or CW) -detecting Doppler shifts from hundreds of locations -colors are encoded to display varying hues -autocorrelation is used to manipulate data -color hue- perceived color used to demonstrate direction, reds & blues -luminance-brightness of color displayed
posterior shadowing
-echogenic structure reflects the majority of sound -shadowing occurs over tissues that are deep to echogenic structure -occurs posterior to structures w/ high attenuation -no sound waves are transmitted so area is black -air creates a dirty shadowing effect posteriorly due to scattering of sound waves
wall filter
-eliminates low freq Doppler shifts from display -used to reduce clutter/flas/ghosting artifacts -has no effect on higher velocity flow displayed on image, will not elimate aliasing
High pass filter
-eliminates low magnitude Doppler shifts that are created from moving anatomy rather than -rejection junction for Doppler -increasing filter setting will reduce appearance of low magnitude Doppler shifts
thermal (heat)
-friction produced from vibration of sound in tissue -amount of heating is determined by acoustic frequency, intensity, beam focusing, and tissue perfusion -caused by sound absorption by tissues
potential errors of doppler
-improper sample location #1 reason missing a stenosis -improper probe position -improper angle of incidence -large sample size -aliasing due to structure depth
end diastolic velocity (doppler measurements)
-measure peak velocity at end of cardiac cycle (end diastole) -used to evaluate resistance in vascular beds distally -increased anegrade flow in diastole indicates low resistance vascular beds distally -absent or retrograde flow in diastole indicates high resistance vascular beds or stenosis/occulsion distally
aliasing
-most common doppler artifact -misrepresenation of Doppler signal due to PRF limitations -causes waveform to "wrap around" from top to bottom on map/baseline -increases w/ higher frequency probes solutions: 1. increase scale 2. lower freq probe 3. change angle of incidence 4. adjust transducer approach to decrease distance to vessel 5. adjust baseline 6. switch to CW probe
mechanical index
-peak rarefactional pressure divided by square root of transducer frequency -lower frequencies produce higher MI and greater risk of cavitation - adusting power will adjust MI -no bioeffects noted at MI less than 0.4
phantom testing
-phantom is used as standard for testing US system functionally -required for system calibration & to satisfy medical/legal needs for facility
noise/speckle
-produced by interference of reflected waves from many tiny reflectors -more speckle seen w/ lower frequency transducers -scattering causes wave interference, resulting in a "speckled" or granular appearance of a homogeneous structure ex: liver, spleen, kidney & thyroid -degrades contrast & spatial resolution -reduces signal to noise ratio b/c is increased
beam width artifact
-reduced by narrowing the width of beam w/ focusing -if beam is wider than the diameter of structure, the normal structures that lie immediately adjacent to lesion are included in beam width -echotexture of adjacent structures is averaged to that of the lesion -it causes artifical echo placement in anechoic structures
quality assurance
-required to medical and legal reasons -tesing should be performed under predetermined well definded guidelines w/ constant settings -phantoms should provide measurable data
system assessment
-requires tests performed under specific and standaraized conditions -requires constant or standard instrument settings -should use phantom w/ measureable and reportable characteristics
Doppler interpretation
-resistance in distal vascualr bard is primary factor that determines resistance characteristics of arterial flow pattern on Doppler -anytime monophasic waveform is seen an extremity = abnormal -biphasic/triphasic vaveform seen w/ an organ = abnormal
focal zone banding
-seen w/ multiple focal zones -image is created by pasting together the individual images obtained from diff depths corresponding to different focal zones
color priority/threshold
-sets level of gray brightness on 2D image where color will be displayed -lower settings limit display of color -determines if a pizel is displayed as shade of black & white or as a color
range ambiguity
-shallow depth = high PRF -shallow reflectors reflect sound energy that arrives at the transducer before rest of orginal pulse finishes transmitting -a second pulse is transmitted as soon as echoes from first pulse are received -causes "confusion" on echo placement in near field
accleration time
-time from onset of systole to point of max systolic peak -increases as stenosis increases -typically used to evaluate flow in extremities & through heart valves
anisotrophy artifact
-tissues display varied echogenicity depending on angle at which they are viewed -commonly seen as falsely hypoechoic areas of tendon -occures when transducer is not completely parallel to tendon & beam is not perpendicular to tendon -reduced by rocking transducer to make face of transducer more parallel to long axis of tendon
when evaluating a suspected arterial stenosis, a Doppler angle of ____ degrees will produce the most accurate flow velocity.
0; most accurate velocity is obtained with a 0 degree angle between the beam and flow increases, amount of error in the calculation increases.
factors affecting blood flow
1. cardiac function (decreased function, increased function) 2. peripheral resistance 3. vessel compliance (stiffer or more calcific vessels) 4. tone of vascular musculature 5. pattern of branches or collaterals 6. vasoconstriction (tightening of walls) 7. vasodilation 8. viscosity 9. exercise 10. autoregulation
color scale-PRF
1. color scale has a narrow range relative to velocity. if scale is set too low, aliasing will occur; scale set too high, low velocity (diastolic flow) may not be detected
eliminate or reduce aliasing
1. increase the PRF (pratical solution) 2. drop or reposition the baseline (practical solution) 3. elimnate the time-sharing features like "triplex" Doppler 4. use a higher Doppler angle to decrease the frequency shift 5. decrease the Doppler transmit frequency 6. decrease sample volume depth (not always possible) 7. use PRF mode, if available
Pulse Repetition Frequency (PRF)
1. is the number of pulse-echo cycles occuring in one second. 2. ranges from several hundred to many thousands of times per second. 3. is experessed as hertz (Hz); 1000 pulse-echo cycles in one second= 1000 Hz. 4. PRF on most systems is linked to the SCALE control in spectral and color Doppler.
advantages of CW doppler
1. it is not specific for depth ( no sample volume), and it will detect flow in any and all vessesl in the beam path 2. it is useful and convenient for obtaining systolic blood pressures in lower arterial exams 3. NO aliasing artifact
disadvantages of CW doppler
1. it is not specific for depth, and its difficult to isolate specific vessels along the beam path. 2. A limitation of Analog Doppler processing; if venous and arterial flow are within beam path, the frequency information is averaged and waveforms will be distorted.
AIUM test objects
1. line density targets 2. phased out since tissue phantoms were created 3. rods made out of steel 0.75 mm thick plastic case holds fulid within that has same propagation speed as soft tissue
Autocorrelation
1. most color Doppler systems use autocorrelation to generate a color image; multiple pulses sent along a single scan line are analyzed for frequency shift at various depths. (on color Doppler display, there are typically hundreds of Doppler sample sites per scanline
advantages of power doppler
1. no aliasing 2. less angle dependency, color encoding and good filling at 90 degrees 3. improved noise filtering 4. improved sensitivity
Pulses Per Scan line
1. packet size 2. ensemble length 3. color sensitivity 4. color quality
color frame rate variables
1. packet size (pulses per line) 2. density of scan lines 3. PRF 4. color box width color box depth
4 components of QA program
1. preventative maintenance 2. repairs 3. system assessment of all components 4. record keeping
Pulsed Wave (PW Doppler)
1. same piezoelectric elements are used for transmission and reception; they alternate function 2. may consist of a single crystal or an array of elements. In linear array transducers, multiple elements are used together for Doppler. 3. A sample volume or range gate is integral to PW Doppler. It allows a specific region of a vessel to be analyzed.
Wall filters
1. spectral and color Doppler have wall filters, "thump" (high-pass filters) 2. often linked to the PRF scale, as scale increases, so does wall filter level 3. should be set to less than 100 Hz for venous flow detection 4. filters should be set low for detection of low velocities (trickle flow) in a near total 5. wall filters in spectral Doppler eliminate "noise" along the spectral baseline, but if the filter is set too high, can eliminate portion of the waveforms
color Doppler
1. uses multiple scan lines contained within the color box or region of interest (ROI) to create a real-time image of frequency shifts related to movment 2. process must occur fast to be perceived as "real time"
If the input power is 2mW and the output power is 200mW, what is the gain?
20dB; 2mW x 100
Which of the following statements correctly describes annular arrays?
An annular array can electronically focus the beam
sensitivity (gold standard testing)
ability of a test to detect disease when IT IS PRESENT
registration accuracy
accuracy of placement of echoes on screen as related to structure placement in the body when structures is scanned from different windows
vertical depth accuracy
aka range accuracy reported in cm accuracy of depth assessment of structures within the phantom
monophasic
all flow is antegrade during entire cardiac cycle
time gain compensation (TGC)
allows selective amplification of reflections displayed on the image usually near field reflections are diminished and far field echoes amplified compensates for beam attenuation across the depth of the image gain does NOT affect patient exposure
preprocessing
assigning discrete shades of gray to returned echo amplitudes strength or amplitude of received echo determines brightness of pixel on display location of pixel is determined by time of flight changing gain, compression, rejection, gray map during an exam will store images displaying changes only be applied prior to storage in digital memory once preprocessing is changed the image datat is permanently changed for all upcoming images
negative predictive value
calculates how often a negative study is correctly diagnosed
What effect will increased hematocrit levels have on arterial duplex exam?
decreased blood flow velocities; increased hematocrit levels= increased viscosity = thicker blood = decreased flow velocities decreased hematocrit levels = decreased viscosity = thinner blood = increased flow velocities
All of the following can be related to color flash artifact, except:
decreased color gain; color priority refers to the way the machine processes information to superimpose color over 2D image.
changes in beam w/ focusing
decreases the diameter of beam at focal zone increases beam diameter in far field decreases beam diameter in near field
inertia
energy is lost when speed of blood changes w/ systole & diastole of heart
propagation artifacs
occur due to bending (refraction) reflection, or reverberation of sound wve aka refraction artifacts must use two imaging planes to evaluate a suspected artifact
postprocessing
occurs after storage in digital memory refers to determination of brightness level that will be displayed for each gray scal lvel changes in post processing allow the tech to manipulate images after they are captured used on stored & frozen images changed on each image and can be changed back to setting of original image types: gain, rejection, DR cine loop
read magnification
occurs after the info is stored in digital memory, frozen or static image postprocessing function of the system selects a region of original stored image to be displayed does not change # of pixels displayed can cause decrease in spatial resolution, coarse appear.
write magnification
occurs prior to info storage into digital memory during real time scanning preprocessing function of system examples of butons: RES, depth, FOV, scale improves spatial and temporal res
Which of the following correctly describes an annular array?
offers excellent lateral resolution; annular arrays offer improved lateral resolution but degraded temporal resolution. A sector shaped field of view is produced.
amplification
one amplifier for each channel each returning reflection is made stronger/larger for additional processing & storage all signals amplified equally (overall gain) useful signals & noise amplified, no improvement of signal to noise ratio w/ overall gain adjustment controls this by using overall gain control gain = ratio of amplifier output to electric power input measured in dB example: 3dB = increase power x 2 6 dB= increase power x 4
The pulser sends the voltage spike to the ________.
transducer; voltage spikes are sent to the transducer element to produce the vibrations for sound waves.
lateral resolution artifact
two objects side by side appear as one object; related to beam width; occurs when beam is wider than the reflector in the body
BART
"blue away, red towards"
artifacts
"incorrect" reflected information evaluated in at least two planes/views
mechanical (microcavitation)
- also called nonthermal bioeffects -production of and variation in gas bubbles in tissue -seen w/ higher intensitities than normal diagnostic US -stable: seen at lower MI values; bubbles vibrate w/o bursting transient- seen at higher MI values; causes microbubles t collapse or burst
cross talk
- type of mirror imaging -a second copy of Doppler tracing displayed on opposite side of baseline -caused by receiver gain too high or incident angle near 90 degrees -try turning down Doppler gain or using different scanning approach
Doppler US physics
-Doppler shift: math difference between transmitted & received frequencies, occurs when structures are moving toward or away from "listener" - if blood is moving away from transducer, reflected sound has lower frequency -if blood is moving toward transducer, refleted sound has a higher frequency -greater the Doppler angle between the beam & blood flow, greater the amount of error in calculated velocity - doppler shift is inverserly related to speed of sound in medium
spectral broadening
-Pw doppler tracing displays a wider distribution of velocity of blood cells w/ varying degree of arterial blockage -occurs due to turbulence of blood flow & variety of Doppler shifts produced/displayed -# of reflected frequencies is determined by speed of RBC anatomic causes- stenosis, tortuosity &bifurcations technical causes- increased gain, improper sample location (near vessel wall) & large sample size
color doppler hints
-adjust scale, gain, and baseline -decrease size of sample for improved flow visualization -create angle of vessel across the screen, NO 90 degrees -flow must be parallel w/ incident beam -increasing transducer freq increases sensitivity to color flow -adjust color map settings to highlight turbulence & lumen characteristics
PW Doppler
-aka gated Doppler -uses controlled time intervals between transmitted & received sounds to collect info using a single PZT element -depth selected by tech -PRF of pulsed wave system determines sampling rate for Dopp eval -larger sample sizes produces waveform w/ smaller spectral window -nyquist limit indicates highest velocity that can be displayed w/o aliasing -aliasing biggest disadvantage of PW b.c limits velocities that can be evaluated -aliasing can be fixed- lower freq trans, increasing PRF (scale) and adjusting baseline -transducer freq is directly related to Doppler shift
electrical interference
-appears repetitive, consistent artifactual echoes demonstrated on Doppler tracing -frequency of electrical signal is directly related to number of artifact echoes demonstrated in one second -increasing wall filter & rejection settings can aid in eliminating this artifact
spectral broadening
-artifactual fill-in of spectral windown due to system settings -caused by increased Doppler gain, Doppler angle or Doppler sample size -turbulent flow and stenosis lead to spectral broadening & adjusting sytem settings will not produce a clear spectral window
baseline
-demonstrate positive & negative shifts approt. w/o aliasing -adjustments can be used to elminate aliasing -if top of waveform is displayed below baseline, lower baseline and bring it back above baseline
spatial measurements
-describes where to measure intensity in the beam - peak: peak intensity measured in center of beam -average: average intensity measured across entire beam -larger area evaluated, lower intensity of beam
spectral doppler
-displays range of frequency shifts measured or calculated flow velocities -avg rang of detected Doppler shifts = 20-20,000 Hz -doppler shifts are detected along a single line & used to produce a graphic represenation of blood velocities
spectral doppler
-displays range of frequency shifts measured or calculated velocities -avg range of detected Doppler shifts = 20 -20,000 Hz -Doppler shifts are detected along a single line & used to produce a graphic representation of blood velocities -contain spectrum analyzers to produce graphic displays -brightness of displayed signal is directly related to reflected signal strength (# of red blood cells moving at that speed)
CW Doppler
-do not use b-mode imaging -separate transmit & receive PE elements -flow is detected at region where transmit & receive beams overlap -NO damping material required b/c pulse is always on -calculate blood flow at high velocities -detecting stenosis 85% or higher -cannot determine location of highest velocity called range ambiguity
uniformity
-evaluating compensation controls (TGC)
potential errors
-flow perpendicular to US beam -color scale settings too high for flow velocity present -large sample size -small packet size -gain settings too low
analog doppler
-graphical recording of pulsatile Doppler in a non-spectral (in fom of compressed, thin-line analog tracings) or strip chart recording -limiations include: inability to detect flow less than 6 cm/s inability to detect post stenotic turbulence & display spectral broadening underestimates high velocities & overestimates low velocities
peak systolic velocity (doppler measurements)
-highest velocity of flow through a stenosis is identifed at narrowest point in vessel or distal to focal point of stenosis -measure peak velocity of flow during cardiac systole -used to evaluate arterial flow for potential stenosis -higher velocities indicate smaller arterial lumen diameters
Doppler angle
-magnitude of shift is dependent on (the cosine of) angle between bloodflow & ultrasound beam -proper setting of angle correction cursor = accurate velocity calculations - best obtainable incident angle is used to provide Doppler shift info is 60 degrees -incident angle increases to 90 degrees, Doppler shift detected decreases -90 degree incident angle will yield a Doppler shift of zero -cosine of 90 degrees is 0 -a 0-degree Doppler angle provides lowest & most accurate calculated velocity
quadrature phase detection
-methods used to determine direction of blood flow for bidirectional Doppler systems -requires 2 speakers to allow audible display of signal, one for flow toward and one for flow away from transducer
color sample angle
-optimum angle between sample box & blood flow is 0 degrees or parallel to flow -steering sample box helps to avoid 90 degree insonation angle -incident angle of beam used to evaluate flow in a vessel moves closer to 90 degrees, color Doppler will decrease until it is absent
lobe artifacts- grafting lobes
-seen in transducer arrays -most commonly affect linear arrays -weak off axis lobes that decrease lateral resolution -causes clutter through main axis of sound beam -can cause reflectors to appear in incorrect locations & multiple locations -can cause an anechoic structure to fill in w/ echoes
lobe artifacts- side lobes
-single element probes -weak, off axis lobes that decrease lateral resolution -processes reflections from off axis beams as part of reflections from main beam & artifact is shown on image -can cause reflectors to appear incorrect locations & multiple locations -can cause an anechoic structure to fill in w/ echoes -increasing rejection or decreasing compression can help eliminate the low level artifactual echoes
clutter
-unwanted Doppler display patterns caused by motion or breathing -aka color flash, color bleeding , color ghosting -filters used: high pass, low-pass
range ambiguity
-unwanted reflected information from locations other than desired sample location -seen w/ Doppler evaluation at shallow depths, high PRF
sample volume depth
-used to evaluate flow in specific locations -more superficial structures provide better color display w/ faster frame rate & improved temp res
thermal index
-used to monitor patient exposure -ratio of power produced to power needed to increase temperature in tissue by 1 degree -reducing output power will reduce TI - no thermal bioeffects have caused adverse effects when tissue temp has increased less than 2 degrees C
correcting grafting lobes- apodization
-varying voltage applied to different elements in an array that are forming the same pulse -maximizing voltage to the central elements and reducing the voltage to outer elements will reduce artifact
twinkle artifact
-vertical stripe of mosaic color pattern seen posterior to highly reflective objects (not related to blood flow)
Autocorrelation provides some information
1. direction (sign= negative or positive) 2. average or mean frequency shift 3. power or amplitude 4. variance (freq spread, turbulence) 5. 3 pulses per scan line
disadvantages of power doppler
1. high persistence 2. lack of aliasing 3. no velocity encoding 4. absence of direction encoding in many systems 5. not able to demonstrate flow turbulence
Fast Fourier Transform (FFT)
1. processes thousands of Doppler shifts each second and subdivides the frequency shifts into "bins" of similar data 2. frequency shift is displayed in the vertical axis on the spectral display 3. time is displayed on the horizontal axis of the spectral display 4.amplitude or power, is displayed as brightness of each pixel in the FFT spectral display. The higher density of reflectors at a given velocity, the higher number of frequency shifts distributed in each "bin". The higher the "bin" density the brighter the pixel on the display screen.
linear arrays
1D array: elements side by side w/ long axis & fired along parallel axis requires a lens to focus beam along short axis most transducers used today are 1D arrays stand off pad- used to adjust elevation focus 1.5D array: elements side by side w/ long axis but are etched parallel to long axis to create multiple elements in short axis allow focusing along long axis & short axis
b mode
2D imaging, amplitude of reflected wave demonstrated as a certain brightness level on screen x-axis: depth z-axis: brightness (amplitude) of reflection no y axis on b mode
The spatial pulse length is 4mm. What is the minimum axial resolution?
2mm; axial resolution = 1/2 spatial pulse length
3D/4D imaging
3D- creation of an image based on data acquired during 2D uses length x width x height to produce 3D preprocessing function- image acquistion postprocessing function- image presentation 4D imaging is real time 3D imaging 4D- length x width x height will be displayed over time
annular array
5 concentric, ring shapped piezoelectric elements that produce a cylindrical beam sector shaped image mechanical steering electronically focused by timing voltages to diff elements
fields vs frames
CRT spatial resolution id determined by # of lines used to create each field/frame minimum of 15 Hz frame rate is required to produce a flicker free image for human eye
analog to digital converter
Converts analog signals into digital signals.
Piezoelectric element
Converts voltage pulses to sound pulses quartz is commonly used thickness = 1/2 wavelength of sound produced at element; thicker the element, the lower the operating frequency wider the element diamter- lower beam intensity higher freq transducers offer less penetration but better image resolution higher operating freq produce images w/ improved axial & lateral
Doppler Tissue Imaging
DTI provides ehanced anatomic detail, esp in echo
__________ is defined as the ratio of particle pressure to particle velocity at a given point within the US beam.
Impedance; A rarefaction is the area of negative particle pressure in a sound wave. Dynamic Range refers to the range of levels of gray displayed on the image. Compression refers to adjusting the dynamic range.
Aliasing
It will occur when the Doppler frequency shift exceeds one half of the PRF. also known as Nyquist limit
If the lines per frame increases and the depth remains the same, what other system parameter must change for sound wave production?
PRF; if more scan lines are necessary, the PRF must increase to produce more lines, increasing the # of scan lines during sound wave production will improve that signal to noise ratio of the image but the ratio describes the sensitivity of the system related to image display but not sound production.
Activating which of the following ultrasound functions will cause the largest increase in beam intensity?
PW Doppler; B-mode imaging uses the lowest beam intensity, while PW Doppler requires the highest beam intensity during an ultrasound exam.
Which of the following correctly describes a difference between read and write magnification?
Read magnification displays a selected portion of the original image from data stored in the system. Write magnification allows the selection of a region of the image to display and the US system rescans the area to produce a new image.
____________ is defined as specific area or location where Doppler shift information is being obtained.
Sample Volume; defined as specific area or location where Doppler shift information is being obtained. Spectral broadening and spectral waveforms are characteristics of the Doppler tracing. The Nyquist limit affects the Doppler signal sampling depth/aliasing.
___________ is a QA process using the refraction properties of water to evaluate the beam pattern and measure intensity.
Schlieren method
Which of the following factor has no effect on Doppler shift?
Transducer element width; thickness of the element plays a part in establishing the frequency of the transducer. The propagation speed within the media & transducer frequency are important parts of the calculation of Doppler shift.
Which of the following is an advantage of virtual beam forming (VBF) over traditional pulse echo imaging (PEI)?
VBF allows for improved lateral resolution without degradation of temporal resolution.; VBF allows for simultaneous real-time gray scale, color and Spectral Doppler display.
specificity (gold standard testing)
ability of a test to rule out disease when it is NOT PRESENT
accuracy
ability of test to correctly identify disease or lack of disease
contrast resolution
ability of the image display to distinguish tissues due to subtle variations in reflection intensity depends on the # of bits per pixel in image memory more bits per pixel, more shades of grey on the image & contrast resolution improves adjusted by changing dynamic range, rejection, and & contrast setting on monitor b color or colorize functions will improve contrast res defined as decibels per shade contrast res = dynamic range divided by # of shades
temporal resolution
ability to accurately display moving structures over time higher the frame rate, better the temp res determined by frame rate, lines per frame, & depth reducing size of field of view = increased PRF = increased frame rate & improved temp res slowest component determines temp res single focus, narrow sector, and & low line density offers best temp res m-mode has best temp res & color doppler has worst activating harmonic imaging or spatial compounding, increasing imaging depth, increasing FOV, and adding focal zones will degrade temp resolution
sensitivity
ability to dectect LOW echoes accurately
All of the following are advantages of CW Doppler over PW Doppler except:
ability to determine high velocities at exact location; CW Doppler is preferred for deeper vessels and higher velocities. CW Doppler cannot determine the blood velocity at a specific location. It measures all of the blood velocities along the length of the incident beam. CW Doppler is not pulsed, therefore there is no PRF or aliasing.
horizontal calibration
accuracy of placement of echoes in correct position along the horizontal axis of the image evaluates the position of echoes along a line that is PERPENDICULAR to beam
lateral gain compensation
addresses the differences in echo signal laterally across the image used in echo
summer
adds all focused & steered signal components into data for a single scan line dynamic aperture & apodization are also performed during process
dynamic range/compression
adjusts range of grays displayed on image changes contrast level of image lower the DR, more black and white image, higher contrast of image contrast res is improved w/ more shades of grey but image contrast is reduced
compression
adjusts the # of gray levels in this image range of reflected signals exceeds the ability of the system to process & display that many signals needed to maintain the gray scale within range of human vision largest and smallest remain unchanged but in between are adjusted controls compression or dynamic range keys
overall gain
adjusts the displayed amplitude of the reflected sound waves on the entire image changes in gain do NOT affect the beam intensity or signal to noise ratio ALWAYS adjust gain first when image is too dark, and when image is too bright
power output
adjusts the electrical voltage applied to PE elements in transducer changes the energy of beam & increases intensity transmit gain also increases power of the beam
multi-dimensional linear array
aka 2-dimensional array or 2D array matrix of elements improves elevational resolution by reducing slice thickness produce 3D/4D images
sector angle
aka FOV decreasing sector size/angle decreases line density & increases frame rate small sectors have degraded spatial resolution & improved temp res small sector angle = increased PRF & frame rate
damping layer
aka backing layer epoxy resin attached to back of element; cork or putty can be used reduces ringing effect shortens length (SPL) & duration (PD) improves axial resolution by decreasing SPL
Threshold control
aka color priority used to change color display sets minimum gray level on 2D image where color will be displayed necessary to minimize color ghosting/flash artifact & improper placement of color in vessels
spatial compounding
aka compound imaging scan lines are electronically steered by the transducer in different to evaluate structures using multiple pulses from several diff angles only used on phased arrays b/c requires ability to steer electronically frames averaged together to improve signal-to-noise ratio speckle & clutter reduced posterior shadowing & enhancement reduced or eliminated
axial resolution
aka depth, longitudinal, radial, range, linear minimum distance between reflectors that is required for ability to visualize two different structures that are parallel to beam axis determined by spatial pulse length & pulse duration (set by transducer) shorter the spatial pulse length & pulse duration, better axial resolution axial increases - SPL Decreases as frequency increases, numerical value for axial res decreases and axial res improves spatial pulse length = wavelength x # cycles in pulse ax res = 1/2 SPL does not vary w/ depth, same across entire image cannot be adjust by sonographer unless transducer ischanged
spatial resolution
aka detail resolution varies w/ physical parameters of beam; spatial pulse length & beam width minimum reflector speration required to produce separate echoes smaller numbers indicate better resolution refers to axial & lateral res
pulsatility index
aka gosling index compares the difference between systolic & diastolic velocities to avg velocity of vessel segment must trace waveform across a single cardiac cycle to obtain the mean velocity
temporal compounding
aka persistence or frame averaging uses the avg of previous frames to create the displayed image displays a smoother image & reduces image noise useful for imaging of stationary or slow moving structures limitations include reduced frame rate & degraded temp res
resistive index
aka pourcelot index measurement of vascular resistance compares difference between systolic & diastolic velocities to max velocity of vessel segment PSV- EDV/PSV = RI used to evaluate arterial stenosis low RI values indicate low resistance
Sample Volume
aka range gate length is adjustable. Increasing the size decreases the "ring time" of the Doppler elements during a pulse, i.e. it incerases the spatial pulse length.
elevational resolution
aka slice thickness set by manufacturer a measure of beam width perpendicular to image plane disc shaped elements allow thinnest slices & best elevational resolution, linear transducers have poorest elevational res mechincal focusing w/ lens can be used to reduce slice thickness & improve resolution
volume averaging artifact
aka slice thickness artifact -reduced by narrowing the thickness of the beam or short axis focusing -affects the evaluation of superficial lesions -leads to degraded contrast & spatial resolution -can be reduced by using a standoff pad
sequential linear array
aka switched array approx. 200 rectangular elements placed in a line across the face of transducer voltage is applied to elements in a specific order which is fixed by manufacturer parallel acoustic lines are transmitted mechanical focusing lateral res is improved damage to single element will only cause loss of portion of image produced by that element
propagation speed error
aka vertical misregistration sono equipment is calibrated for propagation velocity of 1540 m/s
edge shadowing/defocusing
also called refractive shadowing caused by a reduction of reflected echoes by bending of the sound waves that touch the margin of a round boundary caused by refraction of sound commonly seen in trans view of blood vessels, cysts, and testicles
persistence
also called temporal compounding color sensitivity uses avg of previous frames to create displayed image used to highlight low velocity flow improves signal to noise ratio on color image
time gain compensation (TGC)
also depth gain compensation corrects for sound wave attenuation that occurs as sound travels deeper in the body different echoes varies w/ reflector depth time of flight is used to determine reflector depth creates uniform brightness from top to bottom of image w/ varied signal amplification controls this function with TGC keys measured in DB far zone = area of maximum amplification
volumetric flow rate
always proportional to blood pressure increased volume = increased blood pressure
frame time
amount of time required to produce a single frame time to create a single scan line multiplied by # of scan lines increased frame time leads to decreased frame rate & temp res
a mode
amplitude mode; reflected echo intensities displayed at a height representing the amplitude of the reflection x-axis- reflector of depth inside structure y-axis-amplitude of reflection
evaluating test results (gold standard testing)
an accepted test that is assumed to be able to determine true disease state of a patient, regardless of positive and negative test
frequency compounding
an image is usually created using all of the frequencies in the entire reflection of a sound pulse frequency compounding divides the reflection into smaller segments of limited frequency & the image is created from each of these smaller segments improves signal to noise ratio, spatial resolution & image quality reduces speckle & clutter artifacts
___________ is the process that is performed in the beam former where the output voltage is varied to decrease the formation of lobe artifacts.
apodization
dead zone
area closest to transducer that cannot produce an accruate image due to reverbertaion measured from top of phatom to depth that uniform tissue is identified dead zone depth-thin as possible
far field
area of image farthest from face of transducer starts at focal zone & extends deeper into tissue aka fraunhofer zone beam divergence occurs in far field
near field
area of the image near face of transducer beam diameter decreases as it nears the focal zone ends at focal zone aka fresnel zone
Apodization is a function of the:
beam former; it generates the voltages applied to the transducer. It determines the PRF, frequency and intensity of the beam.
display controls
brightness- overall lightness of the image, determines range of brightness levels seen on screen contrast- the measurement of difference in light intensity between brightest white & darkest black
positive predictive value
calculates how often a positive study is correctly diagnosed if test result is positive, PPV is proability that patient actually has disease
new transducer construction
capacitive micromachined ultrasonic transducers (CMUT) use miniature elements that each contain a fixed component & flexible membrane
systole
cardiac contration pushes blood forward through arterial system
reverberation
caused by repeated reflection of sound waves bacl & forth between two closely spaced interfaces appears as multiple reflections serperated by equal spacing looks like steps on a ladder comet tail & ring down are reverbertaion artifacts
overall gain compensation
changes the amplitude of all signals across the image corrects for sound wave attenuation overall gain increases the amplitude of ALL of the reflections of brightness of ALL of echoes on images cannot be used to obtain a uniform brightness across image should be adjusted first then use TGC potentiometers to adjust depth gain
doppler techniques
color Doppler power Doppler spectral Doppler, Pulsed Wave or CW analog doppler tissue doppler
color direction
color Doppler methods assign blue or red color for flow direction, and hue or saturation for variation in freq shift
color box steering
color box can be steered to the right, unsteered-straight down, or to the left
frame rate
color frame rate (FR) is slower than B mode due to the necessity of several pulse transmissions per scan line
power doppler
color hue is assigned to the amplitude or "power" of the moving red blood cells. power is density of blood cells traveling at a certain speed.
blooming
color obscures gray scale display of soft plaque b/c resolution of color Doppler is lower than gray scale
pressure
concentration of force within an area, increases w/ systole
laminar flow
concentric layers of flow w/ slight difference in velocity center layer- highest outer layers- slow due to energy loss plug and parabolic flow are types plug flow- all layers offlow moving at same velocity (aorta) parabolic flow- difference in velocity between layerss, bullet shaped
pulsatility
cont. throbbing or beating, flow in arteries pulsates due to cont. cardiac contractions, venous flow is not pulsatile b/c it is not moved by cardiac contraction
linear phased array
contains approx 200 rectangular elements elements fired at varied times for electronic focusing & beam steering trapezoidal FOV, steer & focus beam
signal processor
contains bandpass filter provides amplitude detection/demodulation performs compresssion
analog to digital converter
convert electronic analog voltages to numeric digital echo info digital information is a series of #'s that correspond w/ echo placement & brightness allows for further processing of echo info prior to display & storage
calorimeter
converts acoustic energy into heat calculate total power of us beam
thermocouple device
converts acoustic energy into heat measure beam intensity at specific locations
demodulation/direction
converts signal from radiofrequency form to amplitude form (video form) rectification- converts all negative voltages into positive voltages smoothing- evens out the peaks of signals on new waveform not adjustable main purpose- prepare the signal for a CRT or TV monitor
mirror image
created as sound reflects off a strong reflector appears as a second copy of structure deeper on the image diaphragm commonly exhibits this phenomenon trachea can also cause artifact in soft tissues
harmonic imaging
creating image using sound reflections at 2X the fundamental frequency second harmonic frequency = 2 x fundamental frequency harmonic frequencies are created by tissue boundaries during transmission of fundamental frequency through the tissue results from non linear behavior of sound waves sound moves slightly faster in regions of compression & travels slightly slower in regions of rarefaction resulting harmonic beam is narrower, smaller side lobes, offers better lateral resolution, improved signal to noise ratio, less clutter w/ improved contrast resolution
Which of the following system adjustments can be used to help demonstrate the presence of posterior shadowing seen with gallstones?
decrease dynamic range; decreasing dynamic range will increase the contrast of the image, causing the posterior shadowing to be more prominent. Increasing the probe frequency will decrease the beam width which will improve focusing and resolution of shadowing effect. increasing compression setting will cause display of more shades of gray on the image.
bernoulli effect
decrease in pressure at stenosis due to increased velocity at the site velocity increases, pressure drops leading to an increased pressure gradient
You are performing a PW Doppler exam. Only 2 cardiac cycles are demonstrated on the screen at one time with the current settings. What adjustment can be made to demonstrate 5-6 cardiac cycles on the screen at one time?
decrease sweep speed
As beam width increases, how is intensity affected?
decreases; as the beam widens, the total intensity is spread across the beam width. The narrowest portion of the beam has the highest intensity and this will also decrease as the beam widens.
fill-in interpolation
decreasing line density while the US sytem fills in the "gaps" between fewer lines w/ averaged information improves spatial resolution allows for faster frame rate w/ improved temp and spatial res usually isolated to sector scanning not needed w/ linear w/ rectangular FOV
Which of the following will increase the duty factor of the pulsed ultrasound probe?
decreasing the image depth; shorter pulses are produced faster which will increase of the time the transducer is emitting pulses. If transducer is spending more time emitting pulses, the duty factor increases.
depth
deeper the structure being evaluated, lower the PRF and frame rate PRF = # of ultrasound pulses emitted per second deeper the structure being evaluated, higher (longer) PRP axial resolution is constant at a set depth, but lateral resolution varies w/ shape of beam temp resolution improves as imaging depth is reduced
variance
degree of variablity of mean velocity at different depths in sample color not only varies along vertical aspect of color display, but left to right typically displayed as green scale on red/blue display used to highlight flow turbulence
scan line density
density or number of scan lines affects the color image and the frame rate; the higher the line density (high # of scan lines within the color box, better color resolution)
The amount of compensation necessary for different echoes varies with reflector:
depth; the amount of compensation necessary for different echoes varies with reflector depth. The time of flight is used to determine reflector depth. compensation is used to equalize the differences in the signal amplitudes from reflectors at different depths.
bandpass filtering
determines a range of acceptable frequencies aka bandwidth rejects the frequencies that are above or below the bandwidth reduces noise on the image & improves signal to noise ratio not operator adjustable
beam former
determines firing pattern of elements in array switching the element between transmit & receive functions optimizes beam formation by coordinating electrical signals w/ nanoseconds delays performs apodization to reduce lobe artifact timing delays during dynamic focusing
resistance
determines rate of flow in arteries & regulated by arterioles high resistance = low flow high resistance requires an increase in pressure to maintain constant flow causes: stenosis, vasoconstriction, organ supply not working
DICOM images
digital imaging & communication in medicine, standard image format for medical community
The vacuum tube monitor receives its electrical signal from which component of the US system?
digital to analog converter
focal depth
distance from transducer to the focal point high frequency, wide diameter transducers will have deepest natural focus
arterial blood flow
due to kinetic & potential energy moving blood flow- kinetic blood moves from areas of high to low
Color Doppler
duplex imaging refers to combining 2D imaging w/ Doppler techinque (color, PW, CW) triplex imaging refers to combining 2D, color and PW or CW Doppler; slower frame rate compared to Duplex imaging colors are encoded to display varying hues color hue-perceived color used to demonstrate direction, reds & blues; represents direction of Doppler shift luminance- brightness of color displayed; represents of Doppler shift
correcting graft lobes- subdicing
each element is divided into subelements which are wired together to operate as single element
digital delays
echo delays used to allow for dynamic receive focusing & steering
transmit steering
electrical pulses are produced in a sloped fashion & excite elements which causes electronic steering of the beam controlled by sonographer using steer button steer left- elements are fired from right to left steer right-elements are fired from left to right
Which of the following can be used for backing material in PW transducer?
epoxy; PW Doppler requires a backing/material that reduces the ringing effect of the pulse. Typical substances used include cork, putty, or epoxy. Using air as the backing material is the same as using NO backing material.
slice thickness phantom
evaluates elevational resolution
spatial resolution
evaulates minimum resoultion capability of system determines min axial and lateral res capability reported in mm axial res refers to smallest distance between two pins located parallel ot beam 6 or more rods are placed in a row at different mm intervals from top to bottom lateral res smallest distance between two pins located side by side 6 or more rods placed at specific depths on the image
mechincal focusing
external- lens, fixed internal- curved element, fixed focal point
frame rate
fixed, automatic or operator adjustable vary with change w/ transducer freq, display depth, & focal zone settings as # scan line increases, frame rate decreases as imaging depth increases, frame rate decreases frame rate can be improved by use of parallel processing, processing multiple lines of signals at same time
biphasic
flow during systole is antegrade & some flow is moving in retrograde during diastole
triphasic
flow is antegrade during systole & diastole, brief period of reversal in betweeen
spontaneous flow
flow is present in vein w/o augmentation
doppler phantoms
flow phantom- simulates moving blood flow evaluates accuracy of detected frequency shifts color Doppler also evaluated
ultrasound hybrid imaging
fusion of two or more imaging modalities to form a new technique ex: PET/CT, SPECT/CT
Blood is flowing toward a 7 MHz transducer; you expect the reflected frequency to be ______ 7MHz.
greater than; when the reflector is moving toward the source, the frequency shift will be greater than the original frequency (positive). When the reflector is moving away from the source, the frequency shift will be less than the orginal frequency (negative)
According to the attached color map, what color will the blood be demonstrated that is moving away from the probe at 30 cm/s and is highly turbulent?
green; variance maps uses green and yellow colors to indicate turbulence. the blood is moving away from the transducer at a speed that does not exceed the scale setting, therefore turbulent flow will be green.
diastole
heart relaxes & refills w/ blood from lungs, forward flow continutes in low resistance arteries
packet size
helps to find a balance between accuracy of color displayed & temporal resolution of image 2D = 1 pulse per scan line color Doppler uses 3-32 pulses per scan line =larger packet size larger packet- decreased frame rates but produce more accurate flow velocity info larger packet- better able to identify low velocity flow more accurately parallel processing can be used to improve frame rate & temp res
Why does the Doppler tracing not touch the baseline on either side? (image)
high filter settings; bc the only velocities that are "missing" from the image are the lowest velocities, this indicates a high filter setting. Incorrect gain setting would cause the entire waveform to be difficult view
signal to noise ratio
high signal to noise ratios produce better quality image improves w/ increased output power increased signal w/ constant noise levels = increased ratio improves w/ coded excitation improves w/ spatial compounding, frequency compounding & increased persistence unchanged by gain adjustments (amplification) b/c of signal & noise are both amplifed
How is density of a medium related to impedance within the medium?
higher densities= higher impedance; tissues with higher density will demonstrate higher acoustic impedance
instruments used to measure intensity of beam
hydrophone-measures acoustic pressure at specific locations within beam (also measures PRP, PRF, and pulse duration) force balance- measures power of beam calorimeter-measures total power of beam by absorption as related to temp thermocouple- measures the power of beam related to absorption of sound at specific location within beam liquid crystals- measures total power of beam by absorption as related to temp
2D image terms
hyperechoic- brighter hypechoic- darker anechoic-w/o echoes isoechoic- same level of brightness heterogeneous- varying echogenicity throughout homogeneous- similar echogenicity throughout
element damage
if PE element is not functioning, data will be missing from image -if probe is single element (mechianical)- entire image will not be displayed -element array- missing info related to just the element that is damaged -linear, sector or vector- area of no reflected as a vertical black stripe; also focus/steer beam -annular array- anechoic horizontal arc of missing data -curved array- vertical line of missing data along radius of curve -being unable to steer color sample box in both directions is also sign of element damage -elements should be evaluated for inegrity, sensitivity, capcitance and intermittent failures
digital to analog converter
if monitor device requires analog info for display, then another conversion is required newer systems do not have this portion of the system
lateral gain
image divided into multiple "vertical" zones that are parallel to the axis of the beam used in cardiac imaging to correct for dropout on the lateral aspect of image to better visualize wall motion
temporal resolution artifact
image flicker w/ low frame rate results in inaccurate positioning of moving structures
dynamic frequency tuning
imaging pulses contain a wide range of frequencies shallow parts of image are created by filtering higher frequency reflections for improved resolution wider bandwidths allow better frequency tuning
color Doppler frequency
in a color duplex imaging system will be lower than B-mode imaging frequency
evaluating venous flow
in most cases venous flow is lower velocity than arterial flow = decrease Doppler PRF reduce wall filter settings to demonstrate more low frequency signals increase gain settings b/c venous signals are lower amplitude than arterial increased color priority & persistence settings will improve of low velocity flow
misregistration/refraction
incorrect placement of object location on image second structure appears more lateral than the actual structure location caused by refraction of beam between two dissimilar media refraction artifact degrades lateral resolution
No flow is detected while performing a Color Doppler evaluation of a normal patent vein. What will improve the color display?
increase color packet size; color packet refers to the # of lines in each sample taken. the more lines in the sample, the better the display. (larger packet size = better color)
If the sonographer decreases the image depth, how will this affect the pulse repetition frequency?
increase; a decrease in image depth will increase pulse repetition frequency, which increases frame rate.
If a sound beam moves from air into soft tissue at an incident angle of 60 degrees, how will the angle of the transmitted wave change?
increase; speed of sound in air is 330m/s and the speed of sound in soft tissue is 1540 m/s. propagation speed increased when the wave entered the soft tissue so the angle of transmission would be greater than 60 degrees.
color quality is affected by axial resolution
increased axial resolution (by using a higher transmit frequency) results in smaller pixel size in vertical axis. (decreasing axial resolution increases pixel vertical length
If blood pressure increases with no change in resistance, what happens?
increased flow rate; if blood pressure increases with constant resistance, the rate of blood flow will increase. If blood pressure increases with an equal increase in resistance, no change occurs in flow rate.
Which of the following will reduce the amount of Color Doppler information displayed on the image?
increased sample size; larger sample sizes cause slower frames rates and less accurate display of color information over time. Packet size refers to the # scan lines per sample. the greater the # of scan lines, better the reflected information & display of color. Increasing transducer frequency will improve color sensitivity and increase the amount of color displayed
matching layer
increases efficiency sound transmission in and out of body protects element, usually made up of plastic, thickness of matching layer measures 1/4 wavelength coupling agent highest impendance is in the PE element imp levels: PE element > matching layer > gel > skin
multiple transmit focal zones
increases pulses per scan line improves lat res decreases frame rate and degrades temporal res beam intensity is increased at each focal point w/ highest intensity at focal zone closest to face of transducer
____________ removes low amplitude signals and noise from the image.
increasing rejection; increasing the rejection (2D threshold) removes low amplitude noise and signlas. Increasing the compression setting is will increase the # of shades of gray displayed on the image, including low level echoes and noise.
velocity scale or PRF
increasing the scale allows display of higher velocities w/o aliasing
direction of flow
insonation angle less than 90 degrees will result in positive shift insonation angle greater than 90 defrees will result in negative shift assess steering angle & match positive & negative shifts to colors on color bar
image former
instead of image processor functions: stores echo info from signal processor, manages the info to determine echo placement on image, forwards processed info to the display
Which of the following correctly describes apodization?
it is performed by maximizing the voltage of the central elements and reducing the voltage to the outer elements; Apdization = varying the voltage applied to different elements in an array that are forming the same pulse.
curvilinear or convex phased array
large number of linearly arranged PE elements (120-250) elements fired at varied times to allow electronic focusing & beam steering produces curved/blunted sctor w/ larger near field footprint uses electronic focusing & steering
friction
layers of blood sliding against each other
spatial resolution artifact
less detail seen w/ low line density
AIUM recommendtiions
limit exam time to shortest time necessary in order to limit ultrasound intensity, always use M-mode instead of PW Doppler to evaulate fetal heart always adhere to ALARA
sector phased array
linear phased array large number of linearly arranged rectangular PE elements small footprint w/ 100-300 elements multiple focal points at varied depths
2D measurements
long images-AP and length of a structure transverse- width of structure volume= length x width x height x 0.523 cm^3
wall filter saturation
low filter settings can cause "audible thumping" of strong signals that causes appearance of bright spikes on Doppler tracing
LCD monitor
low power flat panel display, made up a liquid crystal that is sandwiched between layers of glass or plastic and becomes opaque when electric current passes through it accepts digital info from scan converter, does not require a digital to analog converter
intensity ratios
lowest to highest: 1. SATA 2. SPTA 3. SATP or SAPA 4. SPTP or SPPA
What is the expected appearance of a malignancy on elastography evaluation?
malignant masses demonstrate no defomability
image processor
manipulates scan line data for image processing, sorage, and display performs preprocessing, postprocessing, perisistance, pixel interpolation functions gray scale and color scale digital to analog conversion
nyquist limit
max frequency that can be displayed is 1/2 PRF
What is the proper method used to assess the size of the dead zone?
measure from the top of the image to the depth that uniform tissue is identified; dead zone for a transducer is measured by assessing the depth of the area of reverberation at the top of the image. The depth should be measured from the top of the phantom to the depth that uniform tissue is identified.
Which of the following is a necessary machine setting when performing a contrast evaluation of the heart?
mechanical index set to 0.3 or lower; equip. settings require harmonics to be on, the Mechanical Index (MI) must be set to <0.3. Higher mechanical index levels will cause premature bursting of the microbubbles.
housing
metal or plastic protects internal components from electrical shock lined w/ a thin sheet of metal to reduce outside interference layer of rubber or cork lines
contrast imaging
microbubbles- saline, lumason, definity or optison microbubbles in us contrast agents increase reflectivity of flowing blood mechanical index relates to wave pressure to transmited freq. min MI of 0.1 to use contrast agents; <0.3 MI recommended
AIUM recommendations for us safety
minimize exposure time for a comple diagnostic exam always use minimum output power and highest receiver gain required to produce images (ALARA)
lateral resolution
minimum distance between reflectors that are perpendicular to axis of the beam (side by side) aka angular, tranverse, and azimuthal value is essentially equal to beam diameter far field resolution improves w/ high frequency (narrow probes) focusing improves the resolution in area of focusing improves w/ increasing # of scan lines used per image lateral res - best at narrowest portion (focal point) adjusted by sonographer using focusing & changing sector width
m-mode
motion mode displays reflector movement over time used in cardiac motion in OB & echo high sampling rate used w/ m-mode allows more accurate measurement of rapidly moving structures(cardiac valve leaflets) creates a graphic representation of depth & time x-axis: time (seconds) y-axis: depth
array transducers
multiple elements each connected by a seperate source for electrical impulse (channels) these separate channels are used to steer & focus the beam firing groups of elements at diff times to steer or focus duplex imaging use acoustic lenses to improve elevational resolution w/ a fixed elevational focus
3D image acquisition and processing
multiple parallel 2d scans are acquired & manipulated for 3D image slices display options include 2D slices, surface rendering or transparent views commonly used for obstetric and cardiac real time 3D imaging is referred to as 4D imaging w/ 4th dimension displayed
color gain
must be adjusted frequently during an exam as the vessel "fill" will change with varying depths and steering directions
focal zone
narrowest portion of sound beam image resolution is best at its portion of the beam
stenosis
narrowing of a vessel lumen highest velocity of flow through a stenosis is at narrowest point of vessel or right at focal point (distal)
therapeutic transducers
no backing or damping material HIGH QF, narrow bandwidth may use focused and unfocused us beam uses thermal effects (absorption) and cavitaion to treat patients physical therapy reduces swelling and edema
pulse inversion imaging
non-linear imaging method used for enhanced detection of microbubble us contrast agents 2 pulses are sent in rapid succession into the tissue & the second pulse is a mirror image of the 1st 2 reflections are merged upon receipt by the system linear reflection is the dominant factor in imaging tissues degrades temp res but improves spatial & contrast res
traditional system operation
one-to-one correspondence of transmitted ultrasound & related scan line for image production # of pulses emitted is directly related to # of scan lines displayed
digital scan converter
part of image storage component contains 3 parts : 1. analog to digital converter, digital memory and digital analog converter
digital memory
part of scan converter stores converted digital info prior to display after preprocessing functions are complete, data is sent to storage uses binary # system to establish the # of shades of gray displayed a group of bits are assigned to each pixel to store the shade of grey displayed a group of 8 bits is called a byte RAM: random access memory can be revised by user ROM: read only memory, can not be revised by suer
coded excitation
performed in pulser uses frequency modulation of transmitted sound to improve the image creates long sound pulses that contain wide bandwith = increased power & penetration increases signal to noise ratio & improves image quality improves penetration improves axial and contrast res
distal augmentation
performed to assess venous flow response lightly squeeze musucular portion of patient's calf/forearm or have patient flex their foot/hand quickly while listening w/ Doppler more proximally normally increases flow toward the heart followed by lack of flow reversal & flow normalization toward heart
Which of the following console controls can be used to increase the number of scan lines used in a color image?
persistence; increased persistence settings increase the number of scan lines used to create the image and reduce the frame rate.
electronic focusing
phased- electronic adjustable by technologist allows multiple focal points
memory matrix
pixel- digital pixel element matrix- represents the # of rows & columns of pixels greater the matrix size & number of pixels, better image detail higher number of pixels can produce improved spatial res pixel density does not affect spatial res
cine loop review
post processing function chunk of data is stored in the US system while scanning to allow for reviewing the image while going back several seconds
biplane imaging
postprocessing technique that produces 2 simultaneous images of area of interest images represent data collected in 2 planes that are perpendicular to each other useful in prostate imaging and biopsy
energy types
potential: stored energy of motion, aerosol hair spray gravitational: stored energy related to elevated position, roller coaster kinetic: energy of motion, varies w/ mass, greater mass = kinetic energy; KE=0.5 mass x velocity
Edge enhancement, pixel interpolation, persistence and 3D image acquisition are all types of:
preprocessing
transmural pressure
pressure within veins pushing outward normally low increases w/ venous volume
multi path
primary beam strikes a rounded or roughly surfaced structure and the secondary reflection moves at an angle away from the transducer leads to subtle degradation of the image
pulser
produces electrical signals that are sent to transducer frequency of voltage applied to transducer determines freq of soundwave produced up to 500 volts applied to element determines pulse amplitude, PRF, & PRP operator adjusts power control to adjust voltage to pulser & pulse amplitude increases power will increase signal to noise ratio on image
transmit/receive switch
provides protection for amplifier components from high voltages produced by pulser directs signal traffic to and from transducer
valsalva maneuver
proximal augmentation increase intra-abdominal pressure; stimulate stressing during bowel movement evaulates extremity veins, iliac veins, & IVC flow toward heart should stop w/ no flow reversal augmentation of flow toward the heart occurs upon release augmented flow reversal at onset of valsalva = incompetence of venous valves in that segment
The two main reasons the reflected signals must undergo compression is:
range of reflected signals exceeds the ability of the system to process and display that many signals and it is important to maintain gray scale within range of human vision; there are 2 primary reasons the reflected signal must undergo compression. The range of reflected signals exceeds the ability of the system to process and display that many signals and it is important to maintain gray scale within range of human vision.
The primary advantage of pulsed wave Doppler is:
range resolution; major advantage of pulsed wave Doppler is range resolution or range discrimination.
dynamic range
ratio of largest to smallest voltage transducer detects 120 dB range of reflected amplitudes display 20-30 dB compares 2 voltages ex: 2:1 = 3dB 10:1= 10 dB
beam profiler
records a 3D evaluation of reflected amplitudes Schlieren method: transmitting US beam through water to assess beam pattern by displacement of water molecules
Which of the following statements is true regarding pulse inversion imaging?
reduces frame rate compared to standard 2D imaging; pulse inversion imaging is a non-linear imaging method used for enhanced detection of microbubble ultrasound contrast agents.
If you use a tissue phantom that contains a substance with an average propagation speed of 1600cm/s to evaluate a standard ultrasound system, how will this affect the depth calibration testing?
reflectors will appear more shallow than they actually are located within the phantom
The rectus abdominis muscles are associated with _________, while the diaphragm is associated with ____________.
refraction artifact, mirror image artifact
transducer footprint
region on the face of an us transducer that is in contact w/ patients skin smaller footprint, easier it is to visualize structures through smaller window
arterial pulsatility
related to the # of changes in flow direction during one cardiac cycle
poiseuille's equation
relationship between pressure, flow volume &resistance describe how much fluid (blood) moves through pathway (artery); related to Ohm's law vessel length & viscosity are constant; increases in either one will cause increased resistance
elastography
relative stiffness of a mass related to surrounding tissues when compression is applied stress- force per unit area applied to the tissue strain- increase/decrease in the length of tissue divided by its baseline length solid masses appear dark on the image due to increased stiffness cystic masses appear bright- decreased stiffness malignancies- usually appear larger due to involvement of surrounding tissues which increases overall stiffness
What happens to the attenuation coefficient as the wave travels through soft tissue?
remains constant; attenuation coefficient is determined by the medium through which the sound travels. It will remain constant until the wave enters a new medium.
rejection
removal of low level echoes & non-diagnostic info does not affect "brighter" echoes, only low level reflections adjustable using reject, threshold or supression keys bandwidth filter (not adjustable) wall filter performs this function during Doppler
respiratory phasicity
respiration & muscle contraction are responsible for moving flow through venous system inspiration: decreased intrathoracic pressure increased venous return to heart from upper body decreased flow in lower extremities expiration: increase in intrathoracic pressure decreased venous return to the heart from upper body increased flow in lower extremities
ring down
reverberation caused by tissue-gas interface creates a long vertical stripe composed of small echogenic horizontal lines ex gallstones
systolic/diastolic ratio
s/d ratio used to demnostrate difference between systolic & diastolic velocities higher resistance vasccular beds will have higher s/d ratios used to evaluate flow in fetal umbilicial cord
Which of the following will not change with an increase in gain settings?
signal to noise ratio; gain does not affect the amount of usable signal for image creation, therefore the signal to noise ratio does not increase. Increase gain will increase the amplification of the returned waves and the brightness of the entire image. By increasing the gain settings, you will see more echoes displayed in areas that were previously anechoic.
mechanical focusing
single element transducers can only be focused w/ lenses or curved elements is not adjustable by sonographer lens or cuved element is used to focus beam internal- curved element exernal- acoustic lens
hydrophone
small needle with PE crystal attached to end is placed into beam evaluates amplitude, period, pulse duration, prp important for cavitation risks
edge enhancment
spatial high pass filter used to emphasize changes in brightness across the image to make boundaries of vessel walls & organs more prominent produces 2D images w/ higher image contrast & brighter edges of structures but it also amplifies noise & speckle
edge enhancement
spatial high pass filter used to emphasize changes in brightness across the image to make boundaries of vessel walls and organs more produces 2D images w/ higher image contrast and brighter edges of structures allows for more accurate enhancement disadvantage- amplifies noise and speckle
beam uniformity ratio
spatial peak (SP)/ spatial average (SA)
persistence
speckle reduction sequential frames are avg to produce a smoother image w/ less noise improves signal to noise ratio & contrast resolution reduces frame rate & degrades temp res low persistence- moving structures (cardiac) high persistence- little movement
sweep speed
speed of spectral doppler display 50 mm/s is standard setting changes the amount of flow displayed over time;faster speeds demonstrate shorter intervals of Doppler signals
doppler measures velocity not speed
speed- measures of magnitude, any distance, divided by unit time velocity- measure of magnitude & direction, positive or negative direction to related to starting point
cardiac strain imaging
strain occurs naturally w/ contraction of cardiac muscle
contrast resolution
structures of different densitites are placed within phantom tissue background is reference point at 0dB - negative values: less echogenic or anechoic structure -positive values- more echogenic structure
hemodynamics
study of blood & how/why it moves
dosimetry
study of ultrasound exposure related to potential bioeffects
systemic vs pulmonary circulation
systemic: heart-aorta-arteriorles-capillaries-venoules-veins-heart pulmonary: heart-pulmonary artery-lungs-pulmonary veins-heart
Which of the following will be negatively affected by spatial compounding?
temporal resolution; bc multiple pulses from different angles are averaged to produce each frame, frame rate is decreased. When frame rate drops, temporal resolution is degraded. Spatial compounding aids in the reduction of noise or speckle artifact on the image. Spatial resolution and the signal to noise ratio will improve spatial compounding.
beam divergence
the gradual spread of the ultrasound beam in the far field higher the element frequency, less beam divergence
Spatial resolution is:
the minimum reflector separation required to produce separate echoes.; axial and lateral resolution are types of spatial
endocavity probes
tightly curved phased arrays limited by imaging depth & degraded lateral res at greater depths closer to structures = higher freq = improved spatial res wider sector field but limited by depth
Which of the following parameters is displayed on the x-axis on a Doppler tracing?
time; doppler shift frequencies are displayed on a tracing as a function of time: x- axis = time, y axis + Doppler shift
pulse delays
timing delays used for sequencing, phasing, & creating amplitude version these delays are necessary for system to perform beam scanning, steering, transmit focusing & aperature & apodization single pulse enters pulse delay circuitry, multiple delay pathways that pulse travels through each delay pathway coordinates w/ separate element & combination is called channel # of channels does not exceed the number of elements in array higher numbers of channels allow for improved control of beam formation
mechanical transducers
transducer head filled w/ a fluid contains a motor earlier probes used a single element, annular arrays used in later mechanical probes sector FOV fixed focus cannot provide live display if single element malfunctions, entire image is lost mechanical focusing mechanical steering
electronic focusing
transmit focusing: requires at least 3 rows of elements that are fired w/ variable timing controlled by sonographer using focal zone adjustment focal zones = lateral res constant output power w/ added focusing will increase beam intensity
Which of the following techniques will lead to degraded lateral resolution?
trapezoidal field of view on linear array; increasing the size of the FOV by steering the beam into a trapezoidal shape will lead to increased beam divergence. Lateral resolution is degraded with wider beams.
axial (aka depth) artifact
two objects at different depths appear as one object; related to pulse length; ocurs when pulse is longer than the reflector in body
vector array
type of linear phased array trapezoidal imaging format slightly smaller footprint than sector wedge shaped image has flat top w/ wider FOV in near field employs electronic steering & focusing used for echo, neonatal
b-color
type of postprocessing assigns shades of color, instead of shades of gray, to echo info assess subtle differences in tissues improves contrast resolution
panoramic imaging
type of preprocessing image created by sliding the transducer in a direction that is parallel to the imaging plane new echo info is added to the previous image as transducer moves allows for image documentation beyond the normal field of view of transducer
comet tail
type of reverberation numerous repeated reflections between 2 structures in close proximity multiple reflections from a highly reflective object forms a single short hyperechoic line parallel to US beam (shorter than ring down)
Which of the following is a limitation of Analog Doppler?
unable to detect post stenotic turbulence and spectral broadening; cannot detect flow less than 6cm/s, is unable to detect post stenotic turbulence and spectral broadening and usually underestimates high velocities and overestimates low velocities.
How can you adjust the elevation focus to a more superficial location in a 1D array transducer?
use a stand off pad; elevation focus in a 1D array transducer is set by an acoustic lens inside the transducer and is fixed. Placing standard 1cm stand off pad in front of transducer can move the focus to a level that is 1 cm more superficial in the tissues being scanned.
Capacitive Micromachined Ultrasonic Transducers (CMUT):
use miniature elements that each contain a fixed component and a flexible membrane
tissue equivalent phantom
used for b-mode quality control contains a tissue-mimicking water based material that simulates the echotexture of normal liver measures dead zone, resolution, penetration, distance accuracy and gray scale characteristics
gray scale map
used to adjust contrast resolution performed as preprocessing or postprocessing function preprossing- changing the map while scanning real time postprocessing- changing the map after image is stored in memory of the system
rejection
used to eliminate low amplitude reflections & adjust image contrast increased rejection removes more low amplitude reflections to produce a more black and white image increased rejection increases image contrast
focal zone
used to improve lateral resolution single or multiple multiple focal zones decrease frame rate & degrades temp resolution
fill in interpolation
used to overcome increased distance between scan lines in far field of sector transducer improves spatial res by filling in missing data from spaces between scan lines allows for more well defined borders of a round mass or circular structure
Which of the following correctly describes m-mode?
uses a very high sampling rate; m-mode evaluation offers better temporal resolution than 2D imaging.
Which of the following correctly describes dynamic aperture?
uses more crystals to receive deep reflections than to shallow reflections; dynamic aperture is a type of receive deeper reflections than to receive shallow reflections. It will reduce the appearance of lobe artifact.
continuous wave (cw) doppler
uses two piezoelectric elements; one constatnly transmitting and other is continuously receiving
correcting graft lobes- dynamic aperture
using only a few elements to listen to returning echoes narrows the beam into returned
beam steering
using timed pulses to steer the transmitted beam electronic steering allows a linear probe to produce a trapezoidal image & phased sector array probe to produce a sector FOV increasing the steering angle of a 2D image will increase the production weak, off axis beams that lead to lobe artifact color Doppler uses electronic steering to adjust the sample box angle so beam is more parallel to blood flow to improve flow PW doppler uses electronic steering to adjust cursor placement during Doppler evaluation so the beam is more parallel to blood flow
cathode ray tubes
vacuum tube which consists of 1 or more electron guns, internal electrostatic deflection plates/coils, and phosphor screen electron beam is focused and directed at phosphor screen
color map
varied color assignments to doppler shifts pre or post processing function
How is focusing performed using the reflected portion of the beam?
varying the # of PE elements used to receive the reflected echoes; receive focusing is performed by varying the # of PE elements used to receive the reflected echoes
cell muscle pump
veins act as reservoirs muscle contractions move flow through venous system toward heart cometent vavles allow undirectional flow effective pump reduces blood statsis/pooling in legs
velocity vs variance mode
velocity: colors on top of stripe indicate blood flow toward probe & colors on bottom of the stripe indicate blood flow away from probe color change w/ velocity variation always seen up and down the stripe very light or white color display indicates flow velocites near top of scale variance: used to determine turbulence & represent velocity colors on top of stripe indicate blood flow toward probe & colors on bottom of stripe indicate blood away from the probe colors on left- laminar flow colors on right- turbulent flow color change w/ velocity variation always seen up & down stripe and left to right green & yellow indicate turbulence on variance map
kinetic energy reduced or "lost" in blood vessels due to:
viscosity- thickness of blood, thicker blood flows more slowly; increased hematocrit = decreased flow velocity; anemia = thin blood = increased flow velocity
hydrostatic pressure
weight of column of blood inside the vessels calculated by multiplying fluid density x gravity x height of column equal to zero at level of the heart supine HP = 0 mmHg throughout body standing: HP = 100mmHg at ankle HP=0mmHg at heart HP= -30mmHg at head