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The flashcards below were created by user
closeea
on FreezingBlue Flashcards.
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Which real-time instrument measures the displacement of tissue when a force is applied?
elastography
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If the transmitted frequency is 2 MHz, what is the frequency of the second harmonic?
4 MHz
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Which device applies dynamic receive focusing?
recive beam former
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Which operator control adjusts the transmitted peak intensity?
power
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Which operator control can improve the visualization of weak reflectors, yet increases patient exposure?
power
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Which operator control eliminates low-amplitude noise from the B-mode image?
rejection control
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Which B-mode operator control allows multiple sequential frames to be added together for display in real-time?
persistence
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What does activation of the cine function accomplish?
review of sequence of acquired images
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How is averaging effect enhanced in spatial compounding?
additional beam angles
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What are 2 advantages of the frequency compounding in B-mode imaging?
- 1. emphasize penetration, resolution, or tissue texture
- 2. acoustic noise reduction to improve contrast resolution
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What is the image processing technique that translates pixel values to brightness levels in the displayed image?
gray scale map
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At which processing stage does dynamic receive focusing take place?
receive beam formation
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What signal processing technique eliminates low signal levels and redistributes the remaining signal levels throughout the gray scale prior to display?
contrast enhancement
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What is the purpose of bilinear interpolation?
to interpolate (insert; introduce) the scan data a long the axial and angular directions
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Which zoom adjustment can improve the spatial resolution in B-mode imaging?
write zoom
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What is a disadvantage of write zoom?
field of view is limited
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Which operator control alters image contrast? (2)
- 1. frequency compounding
- 2. dynamic range
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What is the purpose of reject control?
removes weak signals and noise
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What is the purpose of persistence?
increase signal to noise ratio
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What is clutter?
"false" echo signals originating outside the main beam caused by side lobes, grating lobes, and scattering
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What is speckle?
the bright and dark variations in the image, from scattering of multiple small, non-specular reflectors
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What is contrast resolution?
the ability to resolve two objects with similar reflective properties as separate entities
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What is geometric distoration?
deviation from true spatial relationships corresponding to anatomic structures
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What is temporal resolution?
the ability to depict the movement of structures accurately
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Which B-mode imaging technique suppresses speckle?
spatial compounding
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Which adjstment would improve temporal resolution in B-mode imaging?
decrease number of transmit focal zones
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What are the 8 assumptions the machine makes
- 1. transmitted wave travels in straight line path
- 2. attenuation is uniform along the path
- 3. beam dimensions are small
- 4. all echoes originate from axis of main beam only
- 5. all received echoes come from most recent transmitted pulse
- 6. ultrasound wave travels through body at 1540 m/s
- 7. each reflector contributes a single echo
- 8. every signal is derived from a single object and is related to its reflective properties
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Another term for elevational resolution is?
slice thickness
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What effect can the slice thickness artifact have on an image?
fills in hollow structures
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What are the three types of refraction artifacts?
- 1. misregistration refraction
- 2. defocusing refraction
- 3. ghost image
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The artifact that occurs due to vibrations of gas bubbles being insonated by ultrasound is called?
ring down
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When specular reflectors are isonated at oblique angles, resulting in incorrect axial placement of an interface, it is called?
multiple path reflections (artifact)
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Velocity error occurs when?
the actual acoustic velocity in the medium deviates from the calibrated velocity and the measured elapsed time is not accurately converted to depth
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What artifact occurs when sound reflects off a strong reflector and part of the sound energy is redirected toward the same structure, resulting in a duplicated display of the structure placed deeper in the image?
mirror image
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What are two beneficial artifacts?
- 1. enhancement
- 2. shadowing
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Bending of the sound beam after striking a curved reflector, causing edge shadowing, is called?
refraction-defocusing
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What is the doppler effect?
phenomenon in which an apparent change from the transmitted frequency is relative motion between the source of sound and the receiver
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What is observed for a reflector moving at constant velocity with a dopler angle of 90 degrees?
echo frequency is the same as transmit fequency
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What is the sign indicator of the doppler shift frequency if a reflector approaches the transducer at constant velocity?
positive
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Which parameters are included in the equation for doppler shift frequency?
- 1. velocity of sound in medium
- 2. angle betwen directions of movement and beam
- 3. transmitted frequency
- 4. velocity of interface / reflector
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What is a feature of continuous wave doppler?
no upper velocity limit for moving reflectors
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What is the purpose of the wall filter?
to eliminate low frequency doppler shifts from moving anatomy rather than from moving blood cells
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Which signal processing technique enables the direction of motion in pulsed wave spectral doppler?
quadrature phase
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What is the artifactual display of a high-frequency doppler shift at a frequency lower than the true value?
aliasing
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What is a feature of duplex scanning using B-mode and spectral doppler?
facilitates placement of the sampling volume
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