Echocardiography Board Review: 500 Multiple Choice Questions With Discussion

Chapter 2

Questions

1.  21. Doppler shift is typically in:

1.  A. Ultrasound range

2.  B. Infrasound range

3.  C. Audible range

2.  22. Duty factor refers to:

1.  A. Power the transducer can generate

2.  B. Range of frequencies the transducer is capable of

3.  C. Physical properties of the damping material

4.  D. Fraction of time the transducer is emitting ultrasound

3.  23. Duty factor increases with:

1.  A. Increasing gain

2.  B. Increasing pulse duration

3.  C. Decreasing pulse repetition frequency (PRF)

4.  D. Decreasing dynamic range

4.  24. Which of the following will increase the PRF?

1.  A. Reducing depth

2.  B. Decreasing transducer frequency

3.  C. Reducing sector angle

4.  D. Reducing filter

5.  25. Persistence will have this effect on the image:

1.  A. Smoothening of a two-dimensional image

2.  B. Better resolution

3.  C. Eliminating artifacts

4.  D. Spuriously reducing wall thickness

6.  26. Aliasing occurs in this type of imaging:

1.  A. Pulsed wave Doppler

2.  B. Continuous wave Doppler

3.  C. None of the above

4.  D. All of the above

7.  27. The Nyquist limit at a PRF of 1000 Hz is:

1.  A. 500 Hz

2.  B. 1000 Hz

3.  C. 2000 Hz

4.  D. Cannot calculate

8.  28. The Nyquist limit can be increased by:

1.  A. Increasing the PRF

2.  B. Reducing the PRF

3.  C. Neither

9.  29. The Nyquist limit can also be increased by:

1.  A. Increasing transducer frequency

2.  B. Reducing transducer frequency

3.  C. Reducing filter

4.  D. None of the above

10. 30. Aliasing can be reduced by:

1.  A. Decreasing the depth

2.  B. Increasing the PRF

3.  C. Reducing the transducer frequency

4.  D. Changing to continuous wave Doppler

5.  E. All of the above

11. 31. What is the purpose of the depth or time gain compensation process adjusted by the echo cardiographer and performed in an ultrasound's receiver?

1.  A. Corrects for depth attenuation and makes the image uniformly bright

2.  B. Eliminates image artifacts

3.  C. Eliminates aliasing

4.  D. None of the above

12. 32. Which of the following increases the Nyquist limit?

1.  A. Increasing the depth

2.  B. Reducing the sample volume depth

3.  C. Increasing the transducer frequency

4.  D. None of the above

13. 33. The maximum Doppler shift that can be displayed without aliasing with a PRF of 10 kHz is:

1.  A. 5 kHz

2.  B. 10 kHz

3.  C. Depends on depth

4.  D. Cannot be determined

14. 34. The PRF is influenced by:

1.  A. Transducer frequency

2.  B. Depth of imaging

3.  C. Both

4.  D. Neither

15. 35. Two identical structures appear on an ultrasound scan. One is real and the other is an artifact, the artifact being deeper than the real structure. What is this artifact called?

1.  A. Shadowing

2.  B. Ghosting

3.  C. Speed error artifact

4.  D. Mirror image

16. 36. What is influenced by the medium through which sound travels?

1.  A. Wavelength alone

2.  B. Speed alone

3.  C. Both wavelength and speed

4.  D. None of the above

17. 37. Image quality on an ultrasound scan is dark throughout? What is the first best step to take?

1.  A. Increase output power

2.  B. Increase receiver gain

3.  C. Change to a higher frequency transducer

4.  D. Decrease receiver gain

18. 38. All of the following will improve temporal resolution except:

1.  A. Decreasing line density

2.  B. Decreasing sector angle

3.  C. Increasing frame rate

4.  D. Multifocusing

19. 39. Sound travels faster in a medium with which of the following characteristics?

1.  A. High density, low stiffness

2.  B. Low density, high stiffness

3.  C. High density, high stiffness

4.  D. Low density, low stiffness

20. 40. Which of the following is associated with continuous wave Doppler compared to pulsed wave Doppler?

1.  A. Aliasing

2.  B. Range specificity

3.  C. Ability to record higher velocities

4.  D. All of the above

Answers for chapter 2

1.  21. Answer: C.

Doppler shift resulting from moving blood is generally audible as it is the difference between the transmitted and returned ultrasound frequency. One can hear them during Doppler examination. Audible frequency is 20–20 000 Hz.

2.  22. Answer: D.

It is pulse duration divided by pulse repetition period. Typical value for two-dimensional imaging is 0.1–1% and for Doppler it is 0.5–5%. Example for a 2 MHz transducer: Period = 1 s/frequency = 1/2 000 000 or 0.0005 ms. The wavelength in tissue is 0.75 mm (period = 0.0005 ms or 0.5 µs); if two periods are in a pulse then pulse duration is 1 µs or 0.001 ms and if PRF is 1000 Hz (pulse repetition period will be 1 ms or 1000 µs) then the duty factor is 1µs/1000 µs = 0.001 = 0.1%.

3.  23. Answer: B.

Proportional to pulse duration if the PRP is constant. If pulse duration is constant, decreasing the PRF will reduce the duty factor by increasing pulse repetition period. Please see explanation for question 22. Gain and dynamic range have no effect on duty factor.

4.  24. Answer: A.

Reducing depth reduces time of flight of ultrasound in the body and hence will increase the PRF. Transducer frequency, sector angle, and filter have no effect on PRF.

5.  25. Answer: A.

Persistence is the process of keeping the prior frames on the display console, and this will smoothen the image. This reduces random noise and strengthens the signal. However, fast-moving structures can produce artifacts and make the structures look thicker than they are. Some of the other smoothing algorithms include interdigitation and blooming to reduce the spoking appearance produced by the scan lines. Persistence does not affect resolution. It is a post-processing tool.

6.  26. Answer: A.

Aliasing or wrap-around occurs when the Nyquist limit or upper limit of measurable velocity is reached. The Nyquist limit is determined by the PRF. Spectral pulsed wave Doppler and color flow imaging are pulsed wave modalities.

7.  27. Answer: A.

Nyquist limit = PRF/2.

8.  28. Answer: A.

Nyquist limit = PRF/2. Hence increasing PRF will increase the Nyquist limit.

9.  29. Answer: B.

Reducing transducer frequency will increase aliasing velocity and reduces range ambiguity. For a given detected Doppler shift, the lower the transducer frequency, the higher is the measured velocity. V in cm/s = (77 Fd in kHz)/Fo in MHz for an incident angle of zero, where Fd is the Doppler shift and Fo is the transmitting frequency.

10. 30. Answer: E.

All of the above. Reducing depth reduces transit time and allows higher PRF. Also see explanation for questions 28 and 29. In continuous wave Doppler, there are separate crystals to transmit and receive crystals and hence no aliasing, thus allowing higher velocities to be measured.

11. 31. Answer: A.

It is post processing, which adjusts for loss of ultrasound that occurs at increasing depths.

12. 32. Answer: B.

The Nyquist limit is determined by the PRF and PRF = 77 000/depth in cm. Hence decreasing the sample volume depth will increase the PRF, which in turn will increase the Nyquist limit.

13. 33. Answer: A.

The Nyquist limit is PRF/2. Hence, a Doppler shift of >5 kHz in this case will cause aliasing. Depth influences the PRF.

14. 34. Answer: B.

The PRF is influenced by pulse duration and time needed for ultrasound to travel in tissue. Increasing depth will increase the time spent in the body. Transducer frequency does not influence PRF but can affect Doppler shift.

15. 35. Answer: D.

Mirror image artifact is a type of artifact where the artifact is always deeper than the real structure and occurs because of the structure or the surface between the two functioning as a mirror. Shape and size of the mirror image depend on shape of the reflecting surface (plane, convex, or concave).

16. 36. Answer: C.

Speed is determined only by the medium through which sound is traveling. For a given frequency, speed will determine the wavelength: the greater the speed, the shorter the wavelength. Period is the time taken for one cycle and is determined by frequency. Medium does not affect the period. Velocity = frequency × wavelength and period = 1/wavelength.

17. 37. Answer: A.

The first best action to take is to increase output power. This will brighten the overall image. If the image is still dark, then the receiver gain should be increased.

18. 38. Answer: D.

Multifocusing will decrease temporal resolution by decreasing the frame rate, whereas all the others will improve temporal resolution by facilitating an increase in the frame rate.

19. 39. Answer: B.

Sound travels faster in a medium with low density and high stiffness.

20. 40. Answer: C.

Aliasing and range specificity are properties of pulsed wave Doppler. Continuous wave Doppler is not associated with range ambiguity. Continuous wave Doppler will also permit recording of higher velocities than pulsed wave Doppler as it is not limited by the PRF as transmitted ultrasound is continuous.