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95 Cards in this Set
- Front
- Back
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What is Temporal resolution?
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Temporal resolution is the ability to see events in time, seperately.
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In order to see a flicker-free image, you need to display at least ___ frames/sec
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In order to see a flicker-free image, you need to display at least 15 frames/sec
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Switched probe
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A switch probe fires elements one at a time
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Sequenced probe
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A sequenced probe fires a group of elements simultaneously
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Phased array probes
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In phased array probes all elements in the array are fired as a complete group but with a very slight time delay between adjacent elements. Changing the delay pattern the beam may be steered in different direction.
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Vector array probes
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Phasing applied to sequenced array in order to provide steering.
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Dynamic aperature
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The transducer aperature is the width of the number of elements involved in a pulse. It is the opening through which the pulse is emitted, and the echoes are allowed to be received by the transducer.
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Multiple Transmit focus
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Multiple transmit focus is the ability to send out pulses that are focused at 2 to 5 different locations within one image. The increased reception time required to complete each scan line will lower the frame rate.
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A Mode
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A mode stands for amplitude mode. it is primarily used for opthamology studies.
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B mode
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B mode stands for brightness mode
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M Mode
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M mode stands for motion mode. Primarily used for heart and fetal studies (blood flow)
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Functions of Pulser and beam former
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The beam former steers and focuses the beam at variable depths. The pulser controls the electrical signal sent to the tx, it determines PRF, PRP and pulse amplitude. It also receives the timing signal from synchronizer
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List 5 receiver functions and what they correspond to
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1) amplification --> output power --> overall gain
2) Compensation --> loss of intensity --> TGC 3) Compression --> contrast resolution --> Log comp/dyn range 4) Demodulation - Rectification and enveloping (NOT sonographer controlled) 5) Rejection --> signal to noise ratio control --> wall filter |
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List the steps in processing a returning signal.
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ADC -- converts analog to digital (electricity into digital)
DSC -- digital storage DAC -- Converts digital into analog (digital into brightness) |
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Memory depth..,. an ultrasound system usually an ______ bit system. A _____ system only displays ___ and ____
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An ultrasound system usually an 8 bit system. A BINARY system only displays 0 (black) and 1 (white)
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List the pre-processing functions
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Pre-processing functions...
Overall gain TGC Depth filter focus log compression persistence write magnification |
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List the post-processing functions
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Post processing
Cine loop Res Magnification Contrast resultion (last 2 done by radiologist) |
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Pixel identifies the _____ picture element. Most tv monitors have ____ pixels
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Pixel identifies the SMALLEST picture element. Most tv monitors have 512x512 pixels
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How many horizontal scan lines are on a CRT display?
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525
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PRF defines _______
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PRF defines the time we have to wait for echoes to return to the transducer (LT)
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Higher PRF = _____ LT
and _____ imaging |
Higher PRF = Lower LT and SHALLOW scanning
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each transit focus requires an independent pulse to be focused at the desired depth. If we have 2 transmit focuses we need to send out ____ pulses along each scan line: one for each focal depth
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TWO
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PRF is influenced by ....
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PRF is influenced by
depth ---> inversely FR --> directly # of foci --> directly LPF --> directly |
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PRF formula (long)
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# of foci X FR X LPF
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Define hemodynamics
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hemodynamics is the study of blood flow circulation. The forces and motion of blood flow
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Define Viscosity
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Viscosity is the resistence of flow offered by the fluid in motion.
Unit: POISE |
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Define pressure gradient and give an example.
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Pressure gradient is the pressure differences divided by the distance between pressure locations.
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If the Pressure Gradient increases. the VFR _____
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If the pressure gradient increases, the VFR increases
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Define Volume Flow Rate
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Volume flow rate is the volume of flow passing through a vessel or location per unit time.
Unit: ML/SEC |
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List the 4 factors that affect VFR and indicate relationship.
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1) Pressure differences --> direct
2) Tube diameter --> directly 3) Tube length --> inverse 4) Viscosity --> Inverse |
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What is the relationship between VFR and resistence.
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Inversely related. VFR is equal to pressure over resistence so the relationship will be inverse.
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What is plug flow?
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Plug flow is steady flow at the beginning of a vessel. Flow is constant thoughout the width of the vessel
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What is laminar flow?
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Laminar flow is fastest in center, slower on the edges due to friction and runs in parallel lines
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What is disturbed flow?
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Disturbed flow is when parallel lines of laminar flow gets altered. Seen pre-stenosis and at bif.
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What is turbulent flow?
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Turbulent flow is chaotic flow. usually seen post-stenosis and at the bulb
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Pulsatile flow is directly affected by _____
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pulsatile flow is directly affected by the BEATING OF THE HEART
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Phasic flow is directly affected by ______
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Phasic flow is directly affected by RESPIRATION
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The reynolds number predicts the _____ which occurs at the number ____
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The reynolds number predicts the ONSET OF TURBULENCE, whoch occurs at >2000
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List the 4 factors used to calculate Rn
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velosity density and diameter
DIVIDED by viscosity |
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Explain the Continuity Rule
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Continuity rule states that VFR remains constant pre, @ and post-stenosis
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Explain the Bernoulli Effect
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The bernoulli effect ... there is a drop in pressure at stenosis associated with increased flow speed in order to maintain continuity rule
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What is the doppler effect?
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The doppler effect is a change in received frequency as a result of relative motion
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An increased frequency indicates that flow is moving _____ the Tx
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An increased frequency indicates that flow is moving TOWARDS the Tx
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A decreased frequency indicates that flow is moving ____ the Tx
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A decreased frequency indicates that flow is moving AWAY FROM the Tx
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What is the doppler shift frequency equation?
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FD = 2 x operating frequency X velosity X Cosine Theta DIVIDED BY prop speed
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What is the range for doppler frequency?
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20 Hz --> 20 Khz
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Increased operating frequency = ______ doppler shift
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Increased operating frequency = INCREASED doppler shift
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Increased velocity of RBC = ____ doppler shift
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Increased velocity of RBC = INCREASED doppler shift
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increased Cosine = _____ doppler shift
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Increased cosine = INCREASED doppler shift
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Cosine of 90 Degree = ___
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Zero
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Cosine of 0 degree = ___
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1 (max)
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If you scan at _____ no doppler shift will be detected
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If you scan at 90 degrees NO doppler shift will be detected
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Increasing scanning angle = ____ doppler shift
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Increasing scanning angle = DECREASING DOPPLER SHIFT
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List the info derived from color doppler
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1) type
2) prescence/abscence of flow 3) direction 4) mean color velosity of flow |
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What are the controls associated with color doppler?
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Color gain --> increases/decreases amplitude of entire signal
Color box --> adjust sample area Ensemble length --> # of pulses per scan line Velocity range/color bar --> sets PRF or scale limit Wall filter --> eliminates clutter noise Priority --> selects amount of grayscale echoes that are present Persistence --> smooths color flow info |
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Definition of aliasing
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Due to LOW SAMPLING RATE or improper settings.
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Aliasing occurs when _____
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Aliasing occurs when Nyquist limit is exceeded
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The formula for Nyquist limit
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1/2PRF
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List ways to reduce aliasing
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lower doppler shift
-scan shallow -increase scale (PRF) -lower frequency -Increase scanning angle Decrease sample size (will increase FR) Switch to CW doppler (no PRF) |
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What is autocorrelation?
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Autocorrelation is the automatic assignment of color according to strength. Done by the machine
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What information may be derived from spectral doppler?
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Spectral doppler provides specific information regarding the flow that causes doppler shift. It displays the entire range of doppler shift frequencies happening at that particular time
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What is spectral broadening?
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Spectral broadening is wide spectral traces indicating multiple velocities are present in the sample. cvan be seen as vertical thickening of spectral trace @ stenosis AKA window filling
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What controls are associated with spectral doppler?
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Doppler gain
Scale Baseline D-invert Angle correction filter trace range gate sweep |
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What controls are associated with power doppler?
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Overall gain
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What is FFT (fast fourier transform)?
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FFT is the mathmatical technique the ultrasound machine uses to calculate doppler shift in spectral instruments
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CW ... modality
crystals .... duty factor ... PRF |
Continuous wave is a blind modality (image free), two crystals are used (one sending and one receiving) the pulse is always on so DF is 100% and there is no PRF.
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Artifcats are structures on the screen that are...
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Not real
missing do not correspond with actual anatomy Improper brightness, location, size and shape Improper probe position can lead to anatomical errors |
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Section thickness artifact
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Internal echoes seen in anechoic structures (fluid filled). true reflector located outside imaging plane and outside sound beam appears on the screen
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Speckle artifact
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Scattering due to non-specular reflectors or rough surfaces on uneven textures or scattering of sound beam. Appearance: LOOKS GRAINY
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Reverberation artifact
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Multiple equally spaced reflections with decreasing intensities appear because of bouncing effect due to 2 strong reflectors.
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Comet-tail artifact
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Comet tail artifact is caused by interaction with metal particles
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Ring down artifact
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Ring down is due to interaction with air pocket
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Mirror image artifact
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Structures on one side of the reflector are duplicated on the posterior side of a strong reflector
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Refraction artifact
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Lateral displacement of structures. Must have oblique incidence and mediums must have different prop speeds
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Grating lobes artifact
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Grating lobes are seen as lateral displacement of structures caused by electronic Tx
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Side lobes artifact
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Side lobes artifact is lateral displacement of a structure caused by mechanical Tx
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Prop speed error artifact
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Longitudial displacement of structures due to slower/faster prop speeds than normal. resulting in axial displacement
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An area with a high prop speed error will result in object being placed _____ on the display
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An area with a high prop speed error will result in the object being placed TOO CLOSE on the display
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Define Range Ambiguity
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Range ambiguity results from a poor PRF/depth relationship. It is when PRF does not match imaging depth that results in improper placement of reflections
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Axial resolution artifact
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Axial resolution artifact is caused by low frequency. Objects above/below each other are not seen or seen as one large object
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Lateral resolution artifact
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Lateral resolution artifact is caused by imaging outside of the focal zone (either in NZ or FZ)
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Shadowing.
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Weakening of sound posterior to structure due to interaction with strong reflectors or highly attenuating structures. Seen under stones, bones and calcifications
"Day followed by night" |
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Edge Refraction artifcat
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Caused by double refraction. At enterance and again at exit of a cystic structure.
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Acoustic/posterior enhancement
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Caused by weak attenuators. It is the strengthening of echoes distal to weak attenuators. Example; bladder
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A solid mass/fluid filled structure would likely cause _____
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A solid mass/fluid filled structure would likely cause Posterior enhancement
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Bio-effects:
Heat due to ..... |
Heat due to attenuation which includes absorption
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List 2 types of cavitation.
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Stable - gas bubbles that DO NOT rupture
Transient/unstable - gas bubbles that DO rupture |
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Define ALARA
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As low as reasonably achieveable
Low exposure low exams |
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What type of intensity/frequency would likely result in cavitation?
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High intensity and high frequency
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In VIVO refers to studies performed ...
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In VIVO refers to studies performed on live tissue (animals and plants)
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In VITRO refers to studies performed in _____
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In VITRO refers to studies performed in petri dishes and test tubes. It is theoretical explanation
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Tissue equivalent phantoms do what?
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Tissue equivalent phantom simulate
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Test objects are testing what?
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1) Axial resolution & vertical registration
2) lateral resolution & horizontal registration 3) Dead zone |
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String test objects evaluate ____
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Spectral doppler
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Hydrophone evaluates ____
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Hydrophone evaluates acoustic output of Tx
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