7. Artifacts Flashcards
The pulser of an instrument automatically reduces the PRF for deeper imaging to avoid the ______ artifact
a. comet tail
b. grating lobe
c. mirror image
d. range ambiguity
d. range ambiguity
If an echo arrives 143 us after the pulse that produced it was emitted, it should be located at a depth of __ cm. If a second pulse was emitted 13 us before the arrival of this echo, it will be placed incorrectly at a depth of ___ cm.
a. 11, 1
b. 14, 13
c. 13, 14
d. 13, 13
a. 11, 1
If the propagation speed in a soft tissue path is 1.60 mm/us, a diagnostic instrument assumes a propagation speed too ____ and will show reflectors too ____ the transducer.
a. high, close to
b. high, far from
c. low, close to
d. low, far from
c. low, close to
Mirror image can occur with only one reflector. T or F?
False
The most common artifact encountered in Doppler ultrasound is ____.
a. aliasing
b. range ambiguity
c. spectrum mirror image
d. location mirror image
e. electromagnetic interference
a. aliasing
Which of the following can reduce or eliminate aliasing?
a. increased PRF
b. increased Doppler angle
c. increased operating frequency
d. use of continuous wave mode
e. more than one of the above
e. more than one of the above (a, b, d)
The fine texture in soft tissue indicates the excellent resolution that actually exists there. T or F?
False
The fact that a beam, as it scans through tissue, has some nonzero width perpendicular to the scan plane results in the _____ artifact
a. mirror image
b. range ambiguity
c. slice thickness
d. speed error
c. slice thickness
Which of the following can cause improper location of objects on a display? (more than one correct answer)
a. shadowing
b. enhancement
c. speed error
d. mirror image
e. refraction
f. grating lobe
c, d, e, f
Refraction can cause shadowing. T or F?
True (edge shadowing)
Reverberation results in added reflectors being imaged with equal ____.
a. depth
b. separation
c. width
d. brightness
b. separation
In reverberation, subsequent reflections are ___ than previous ones.
a. shallower
b. brighter
c. weaker
d. stronger
c. weaker
Enhancement is caused by a _________
a. strongly reflecting structure
b. weakly attenuating structure
c. strongly attenuation structure
d. refracting boundary
e. propagation speed error
b. weakly attenuating structure
Which of the following can correct or eliminate aliasing?
a. decreased PRF
b. decreased Doppler angle
c. increased operating frequency
d. baseline shifting
e. more than one of the above
d. baseline shifting
Shadowing results in decreased echo amplitudes. T or F?
True
Propagation speed error results in improper ____ position of a reflector on the display
a. lateral
b. axial
b. axial
To avoid aliasing, a signal voltage must be samples at least ____ time(s) per cycle
a. 1
b. 2
c. 3
d. 4
e. 5
b. 2
If the highest Doppler-shift frequency present in a signal exceeds _____ the PRF, aliasing will occur.
a. one-tenth
b. one-half
c. two times
d. five times
e. ten times
b. one-half
When Doppler gain is set too high, which artifact is likely to occur?
a. aliasing
b. range ambiguity
c. spectrum mirror image
d. location mirror image
e. speckle
c. spectrum mirror image
Which artifact should be suspected if one observes twin gestational sacs when scanning through the rectus abdominis muscle?
a. refraction
b. reverberation
c. speckle
d. enhancement
a, refraction (double image)
Range ambiguity can occur in which of the following?
a. imaging instruments
b. duplex instruments
c. pulsed-wave Doppler instruments
d. color flow instruments
e. all of the above
e. all of the above
If the PRF is 4 kHz, which of the following Doppler shifts will cause aliasing?
a. 1 kHz
b. 2 kHz
c. 3 kHz
d. 4 kHz
e. more than one of the above
e. more than one of the above (c and d)
If the PRF is 10 kHz, which of the following Doppler shifts will cause aliasing?
a. 1 kHz
b. 2 kHz
c. 3 kHz
d. 4 kHz
e. none of the above
e. none of the above
There is no problem with aliasing as long as the Doppler shifts are ___ half the PRF.
a. less than
b. approximately equal to
c. greater than
d. all of the above
e. none of the above
a. less than
If Doppler shift is 2.6 kHz, no aliasing would result with a PRF of 10 kHz. T or F?
True
If red represents a positive Doppler shift and blue represents a negative one, what color is seen for normal flow toward the transducer? What color is seen for aliasing flow toward the transducer? What colors are seen for normal flow away and for aliasing flow away from the transducer?
a. red, red, blue, blue
b. red, blue, red, blue
c. blue, red, blue, red
d. red, blue, blue, red
d. red, blue, blue, red
When a pulse is emitted before all the echoes from the previous pulse have been received, which artifact occurs?
a. mirror image
b. range ambiguity
c. slice thickness
d. speed error
b. range ambiguity
When a strong reflector is located in the scan plane, which of the following artifacts is likely to occur?
a. aliasing
b. range ambiguity
c. spectrum mirror image
d. location mirror image
e. speckle
d. location mirror image
Increasing PRF to avoid aliasing can cause the following:
a. baseline shift
b. range ambiguity
c. spectrum mirror image
d. location mirror image
e. speckle
b. range ambiguity
Which of the following decreases the likelihood of range-ambiguity artifact?
a. decreasing operating frequency
b. decreasing PRF
c. decreasing Doppler angle
d. baseline shift
e. increasing pulser output
b. decreasing PRF
Range ambiguity produces which error in spectral Doppler studies?
a. incorrect spectral peaks
b. incorrect gate location
c. intensity too high
d. intensity too low
e. all of the above
b. incorrect gate location
Range ambiguity produces which error in anatomic imaging?
a. range too long
b. range too short
c. intensity too high
d. Doppler shift too high
e. Doppler shift too low
b. range too short
If a pulse is emitted 65 us after the previous one, echoes returning from beyond ___ cm will produce range ambiguity.
a. 1
b. 2
c. 3
d. 4
e. 5
e. 5
If the maximum imaging depth is 5 cm, the frequency is 2 MHz, and the Doppler angle is zero, what is the maximum flow speed that will avoid aliasing and range ambiguity?
a. 100 cm/s
b. 200 cm/s
c. 300 cm/s
d. 400 cm/s
e. 500 cm/s
c. 300 cm/s
Solving aliasing by decreasing operating frequency increases the possibility of range-ambiguity artifact. T or F?
True (less attenuation, greater penetration, later echoes)
If operating frequency is increased to decrease the possibility of range ambiguity (by increasing attenuation), the possibility of aliasing increases. T or F?
True (Doppler shift increases with increasing frequency)
If a pulsed wave Doppler sample volume is located at a depth of 8 cm, the sampled echoes arrive at what time following emission of the pulse?
a. 25 us
b. 50 us
c. 75 us
d. 104 us
e. 117 us
d. 104 us
Which of the following instruments can produce aliasing?
a. CW Doppler
b. PW Doppler
c. duplex
d. color Dopper
e. more than one of the above
e. more than one of the above (b, c, d)
