Ch. 5 Practice Questions Part 1 #'s 451-480 - Doppler Instrumentation and Hemodynamics

E. None of the above -B/c CW Doppler does not have an imposed maximum velocity limit like PW Doppler -In fact, CW Doppler may be used in instances where accurate velocities cannot be obtained w/ PW Doppler

451. What is the maximum velocity limit for a 3 MHz CW Doppler unit operating at a depth of 4 cm? Explain why. A. 40 cm/s B. 200 cm/s C. 2.5 m/s D. 4 m/s E. None of the above

D. 1/2 of the PRF

452. You will see aliasing of the Doppler spectrum whenever the frequency shift exceeds...? A. Twice the PRF B. Three times the PRF C. 1/3 of the PRF D. 1/2 of the PRF E. 1/4 of the PRF

E. -B/c according to the Doppler equation, we cannot detect a frequency shift at an incident angle of 90° and transducer E is firing its beam at a 90° angle to flow

This is an illustration in which five transducers are imaging a vessel at different incident angles. The arrow indicates the direction of blood flow. 458. Which transducer would NOT detect a Doppler frequency shift? Explain why. A. B. C. D. E.

E. All except for E -B/c blood is flowing towards transducers A, B, C, and D, which presents as a waveform above the baseline and away from/not towards transducer E, which presents as a waveform below the baseline

This is an illustration in which five transducers are imaging a vessel at different incident angles. The arrow indicates the direction of blood flow. 459. Which transducer would demonstrate a waveform ABOVE the zero baseline? Explain why. A. B. C. D. E. All except for E.

D. Decrease Pulse Repetition Frequency (PRF) -Slow flow produces low frequency shifts and setting the PRF lower increases the sensitivity to low frequency shifts -At low PRFs there is more time b/w the pulses, which allows time for the slow-moving blood flow to move and be detected by the system -Other methods of improving sensitivity to slow flow include decreasing the wall filter and increasing the Doppler frequency -Increasing the wall filter, decreasing packet size, decreasing color gain, and changing the color map will not improve sensitivity to slow flow

453. You obtained this color Doppler image while performing hepatic sonography. There is no color signal detected within the portal vein. What can you do to improve sensitivity to slow flow? Explain why. A. Increase wall filter B. Decrease packet size C. Decrease color gain D. Decrease Pulse Repetition Frequency (PRF) E. Change color map

D. Pulse/listen cycles per acoustic scan line -For color Doppler, each scan line (line of sight) must be pulsed multiple times -The number of pulses transmitted in 1 second is the Pulse Repetition Frequency (PRF) and the number of those pulses fired on each scan line is the packet size (a.k.a. ensemble length or shots per line)

454. In color Doppler, the term "packet size" refers to the number of...? Explain further. A. Pulses per second B. Sample volumes per scan line C. Scan lines per unit area D. Pulse/listen cycles per acoustic scan line E. Pulses required to create one frame

A. Spectral broadening -B/c the waveform shows fill-in of the spectral window (black area under each wave) and the loss of the spectral window is indicative of spectral broadening -Spectral broadening is associated w/ turbulent flow

455. Which of the following artifacts is present in this Doppler spectral waveform? Explain how you can tell. A. Spectral broadening B. Narrow velocity range C. Aliasing D. Mirror imaging E. Range ambiguity

D. The velocity estimation will be inaccurate -The velocity estimation in Doppler US is based on measurement of the Doppler angle of incidence and b/c the blood flow is not directly visualized, the Doppler angle-correction cursor is aligned parallel to the walls of the vessel at the point of sampling -Any time the angle-correction cursor is not adjusted parallel to the wall, the velocity estimation is in error -If this measurement is underestimated, the velocity of flow will be underestimated and if this measurement is overestimated, the velocity of flow will be overestimated -Underestimating the Doppler angle of incidence will not result in underestimation of the frequency shift, no detection of Doppler frequency shift, mirror imaging artifact, or aliasing of the Doppler spectrum

456. While performing a Doppler study, you underestimated the measurement of the Doppler angle of incidence. What error will result from this mistake? Explain why. A. The frequency shift will be underestimated B. No Doppler frequency shift will be detected C. Mirror imaging of the Doppler spectrum will occur D. The velocity estimation will be inaccurate E. Aliasing of the Doppler spectrum will occur

C. Phase quadrature detection

460. _______________ is a commonly used process for determining direction in a Doppler instrument. A. Zero-crossing detection B. Autocorrelation C. Phase quadrature detection D. Range gating E. Spectral analysis

B. Electronic time delays -A linear array transducer steers the beam for color Doppler in the same way a phased array transducer steers its beam, electronically -The active elements are fired w/ very slight time delays, causing the beam to veer off at an angle from the transducer face

461. What method is used to steer the color beam w/ a linear array transducer? Explain how it works. A. Mechanical B. Electronic time delays C. Electronic voltage variation D. Apodization E. The color beam cannot be steered w/ a linear array transducer

D. A and B -To maintain an adequate frame rate in color Doppler, the B-mode image is compromised by decreasing the number of focal zones to 1 or 2 and by decreasing the scan line density, which results in lower Lateral resolution

462. When color Doppler is activated, what may be reduced in the underlying B-mode image to maintain the frame rate? Explain. A. The number of focal zones B. The scan line density C. The frame averaging (persistence) D. A and B E. B and C

D. Continuous-wave (CW) Doppler -Range resolution is the ability to determine the depth from which an echo has arrived and to accomplish this, the sound must be pulsed, not continuous, so that the echo arrival time from each pulse can be measured -Once the arrival time of the echo is known, the distance to the reflector can be determined -This works b/c we know the speed of sound in tissue and assume it to be constant

463. What Doppler technique does NOT provide range resolution? Explain why. A. Color Doppler B. Power Doppler C. Pulsed-wave (PW) Doppler D. Continuous-wave (CW) Doppler E. No Doppler technique can provide range resolution

C. Color encoding red, Positive Doppler shift -When the Doppler US beam intersects a vessel in which blood is flowing towards the Doppler beam, the frequency of the reflected signal is higher than that of the transmitted signal and is termed a positive frequency shift -All Doppler systems are set up so that positive Doppler shifts are color-encoded red and negative Doppler shifts are color-encoded blue -The specific color map in use determines the shading of red and blue and the colors in b/w

464. You have obtained a color Doppler image of the common carotid artery. If the received ultrasound frequency is greater than the transmitted ultrasound frequency, which of the following statements would be correct? Explain why. A. Color encoding red, Negative Doppler shift B. Color encoding blue, Negative Doppler shift C. Color encoding red, Positive Doppler shift D. Color encoding blue, Positive Doppler shift E. No Doppler shift was detected

B. The Doppler signal being sampled rather than recorded continuously

465. Aliasing is a potential problem in PW Doppler b/c of...? A. The use of high Pulse Repetition Frequencies (PRFs) B. The Doppler signal being sampled rather than recorded continuously C. Dynamic focusing D. The motion of the interface perpendicular to ultrasound wave propagation E. Perpendicular (normal) incidence

A. Relative signal power at each frequency in the Doppler signal -The Doppler signal spectral display depicts the frequency bandwidth and the range of amplitudes in the reflected signal -The amplitude, or signal power, depends on the relative number of RBCs comprising each component of the frequency-shift spectrum

466. What does the Doppler signal spectral display depict? Explain further. A. Relative signal power at each frequency in the Doppler signal B. Depth to each vessel C. Volume flow rate D. Transmit frequency E. Acoustic power

D. Reduce display of low frequency shifts -B/c the wall filter is used to eliminate frequency shifts below a set threshold from the display -For example, if the wall filter is set at 50 Hz, then any frequency shift of 50 Hz or less will not be displayed -Increasing the wall filter helps to eliminate the high-amplitude, low-frequency shift signals caused by movement of the vessel wall -Remember to keep in mind that low-frequency shifts may also be a result of slow flow and therefore, any time the wall filter is increased, the system is less sensitive to slow flow -Increasing the wall filter during Doppler sampling will not increase visibility of low-velocity signals, increase spectral broadening, decrease bandwidth, or reduce aliasing artifact

467. Increasing the wall filter during Doppler sampling will...? Explain why. A. Increase visibility of low-velocity signals B. Increase spectral broadening C. Decrease bandwidth D. Reduce display of low frequency shifts E. Reduce aliasing

A. Improved sensitivity (visibility) to slow flow -B/c increasing the transmit frequency will result in larger frequency shifts from slow flow and thus, improved visibility of slow flow -Increasing the transmit frequency will decrease penetration to flow in vessels deep w/in the tissues -Changing the transmit frequency has a negligible effect on frame rate, flash artifact, and visualization of complex flow hemodynamics (aliasing)

468. Which of the following would be the most likely result from increasing the transmit frequency of the color Doppler? Explain why. A. Improved sensitivity (visibility) to slow flow B. Improved penetration for imaging flow in deep tissues C. Reduced flash artifact obscuring small vessel flow D. Reduced color Doppler aliasing E. Improved visibility of complex flow hemodynamics

C. Increased color writing on the vessel or cardiac wall -B/c the threshold controls the brightness of the shade of gray that the color is allowed to overwrite, so if the threshold is lowered, it is more likely that the color will overwrite the vessel or cardiac wall

469. Which of the following would be the most likely result from lowering the color threshold? Explain why. A. Increased visibility of small vessel flow in a parenchymal organ B. Decreased flash artifact C. Increased color writing on the vessel or cardiac wall D. Increased frame rate E. Improved color penetration

B. Fourier analysis

470. What method is most commonly used to perform spectral analysis for pulsed Doppler? A. Zero-crossing detection B. Fourier analysis C. Reynolds number D. Cross correlation E. Autocorrelation

A. Doppler angle of interrogation near 90° -At a 90° Doppler angle, flow direction cannot be determined and the waveform will be seen on both sides of the baseline

471. During Doppler interrogation of the carotid artery, you detect spectral mirroring artifact. Which of the following is a common cause of this artifact? Explain why. A. Doppler angle of interrogation near 90° B. Doppler angle of interrogation near 0° C. Wall filter set too high D. Pulse Repetition Frequency (PRF) set too low E. Doppler gain set too low

A. Aliasing -B/c w/ an aliased signal, the peak of the waveform is clipped off and appears on the opposite side of the baseline -It starts from the bottom of the image and points up towards the baseline -It does not start from the baseline and point down. That would indicate retrograde flow

472. This Doppler waveform can be most accurately described as exhibiting _________________. Explain how you can tell. A. Aliasing B. Spectral broadening C. Mirror image artifact D. Bidirectional flow E. Saturation

D. Pulse Repetition Frequency (PRF) -B/c aliasing artifact occurs when the frequency shift exceeds 1/2 of the PRF and therefore, the frequency at which aliasing occurs increases as the PRF increases

473. This Doppler waveform is exhibiting aliasing artifact. What system control should be adjusted to optimize this waveform? Explain why. A. Wall filter B. Packet size C. Gain D. Pulse Repetition Frequency (PRF) E. Sample volume size

C. Gain -The gain should be decreased b/c the noise in the background behind the spectrum and w/in the spectral window is the result of the gain being set too high -The background noise would not be affected by changing the sample volume nor by changing the wall filter setting

474. What Doppler control should be adjusted to optimize this Doppler spectral waveform? Explain how and why. A. Wall filter B. Packet size C. Gain D. Pulse Repetition Frequency (PRF) E. Baseline

B. The difference b/w the Transmitted and Received frequencies

475. The Doppler frequency shift is defined as...: A. The difference b/w the Doppler frequency and the Imaging frequency B. The difference b/w the Transmitted and Received frequencies C. The time b/w the Transmitted and Received frequencies D. The rate at which the transducer emits pulses E. The amplitude of the transmitted Doppler signal

B. Increasing the Doppler interrogation angle will increase the frequency shift -Doppler equation: Δf = [2FV(cosΘ)] / C Δf: Frequency shift F: Doppler frequency (transmitted) V: Velocity of the reflector (RBC) cosΘ: Doppler angle of incidence C: Propagation speed of sound -The smaller the angle of incidence, the larger the frequency shift

476. According to the Doppler equation, which of the following statements is NOT true? Explain why. A. Increasing Doppler frequency will increase the frequency shift B. Increasing the Doppler interrogation angle will increase the frequency shift C. Decreasing the reflector speed will decrease the frequency shift D. No frequency shift is detected when the Doppler beam strikes the reflector w/ perpendicular (normal) incidence E. Velocity information can be obtained from the frequency shift if the angle of incidence is known

C. Sampling frequency needed for detecting the Doppler signal unambiguously

477. The Nyquist limit describes which of the following? A. Penetration limit of pulsed-wave (PW) Doppler B. Transmit time of pulsed-wave (PW) Doppler C. Sampling frequency needed for detecting the Doppler signal unambiguously D. Sampling method used for continuous-wave (CW) Doppler E. Method used for determining directional information in a Doppler-shifted signal

D. Amplitude -The z-axis on the Doppler spectrum is represented by the brightness of the dot -The brighter the dot, the greater the amplitude of the reflected signal

478. What information does the z-axis (brightness) on the Doppler spectrum provide? Explain further. A. Velocity B. Velocity range C. Bandwidth D. Amplitude E. Frequency shift

D. Increase the Pulse Repetition Frequency (PRF) -B/c increasing the PRF raises the Nyquist limit and will reduce aliasing, a.k.a. unwrap the waveform -Decreasing the angle of incidence would cause a larger frequency shift for any given velocity and therefore, increase the likelihood of aliasing -The high pass filter does not affect aliasing -To reduce aliasing, the zero baseline should be lowered, not raised -Increasing the Doppler frequency (transmitted) would cause a larger frequency shift for any given velocity and therefore, increase the likelihood of aliasing

479. A waveform from the internal carotid artery obtained at a Doppler angle of 45° shows aliasing. Which of the following choices will help you unwrap this waveform? Explain why. A. Decrease the angle of incidence B. Decrease the high pass filter C. Raise the zero baseline D. Increase the Pulse Repetition Frequency (PRF) E. Increase the Doppler frequency

C. Decrease the color box width -B/c the wider the color box, the greater the number of scan lines that must be fired to create one frame and therefore, decreasing the width of the color box will improve the frame rate -Increasing the packet size will increase the frame rate? -Decreasing the PRF may or may not affect the frame rate, but it is more likely to decrease it rather than increase it -Increasing the scan line density will decrease the frame rate -Adjusting the wall filter will not affect the frame rate

480. While performing a color Doppler exam in the abdomen you have adjusted several system controls and notice that the frame rate has decreased. Which of the following adjustments can you make to improve the color frame rate? Explain why. A. Increase the packet size B. Decrease the Pulse Repetition Frequency (PRF) C. Decrease the color box width D. Increase the scan line density E. Increase the wall filter

A. -B/c for any given velocity of flow, the maximum frequency shift will be obtained at 0° and transducer A is firing its beam at a 0° angle to flow

This is an illustration in which five transducers are imaging a vessel at different incident angles. The arrow indicates the direction of blood flow. 457. Which transducer will detect the largest Doppler frequency shift? Explain why. A. B. C. D. E.