CCI Ultrasound Physics and Instrumentation 5 — Questions and Answers
Question 1: The mechanical index (MI) displayed on an ultrasound machine is most closely associated with the risk of:
- Thermal heating of tissue
- Cavitation and non-thermal mechanical bioeffects (Correct answer)
- Electrical interference
- Reverberation artifacts
Correct answer: Cavitation and non-thermal mechanical bioeffects
MI = peak negative pressure / √frequency; higher MI values indicate greater potential for cavitation and non-thermal mechanical bioeffects.
Question 2: When sector width is reduced on a 2D echocardiographic image, the primary benefit is:
- Improved penetration depth
- Increased frame rate (Correct answer)
- Wider field of view
- Reduced gain requirement
Correct answer: Increased frame rate
A narrower sector requires fewer scan lines per frame, allowing the system to update the image more frequently and increasing frame rate.
Question 3: Which artifact causes a structure to appear duplicated and displaced laterally in an ultrasound image?
- Acoustic enhancement
- Refraction artifact (ghost image) (Correct answer)
- Comet-tail artifact
- Reverberation
Correct answer: Refraction artifact (ghost image)
Refraction at curved tissue interfaces bends the sound beam, causing the machine to misplace the returning echo and display a duplicate or displaced ghost image.
Question 4: In the context of transesophageal echocardiography (TEE), the higher image quality compared to transthoracic echo is mainly due to:
- Use of lower frequency transducers
- Elimination of chest wall and lung attenuation by placing the probe adjacent to the heart (Correct answer)
- Use of continuous wave Doppler exclusively
- Higher gain settings available
Correct answer: Elimination of chest wall and lung attenuation by placing the probe adjacent to the heart
The esophagus lies directly posterior to the heart, eliminating lung and chest wall attenuation and allowing higher frequency transducers that provide superior resolution.
Question 5: The Doppler shift frequency is directly proportional to which of the following?
- The depth of the sample volume
- The velocity of the moving reflector (blood cells) (Correct answer)
- The pulse repetition frequency only
- The wall filter cutoff
Correct answer: The velocity of the moving reflector (blood cells)
The Doppler equation shows that Doppler shift = (2 × f × v × cos θ) / c; shift is directly proportional to velocity of the reflector.
Question 6: Increasing pulse repetition frequency (PRF) in pulsed wave Doppler will:
- Increase maximum measurable depth
- Increase the Nyquist limit, allowing measurement of higher velocities before aliasing (Correct answer)
- Reduce temporal resolution
- Decrease the Doppler shift
Correct answer: Increase the Nyquist limit, allowing measurement of higher velocities before aliasing
Higher PRF means more samples per second; since the Nyquist limit = PRF/2, higher PRF raises the aliasing threshold and allows measurement of faster velocities.
Question 7: A 'comet-tail' artifact seen posterior to a small hyperechoic focus is most likely caused by:
- Acoustic shadowing from calcification
- Reverberation between closely spaced strong reflectors creating a bright tapering trail (Correct answer)
- Side lobes from the transducer
- Refraction at a curved surface
Correct answer: Reverberation between closely spaced strong reflectors creating a bright tapering trail
Comet-tail artifacts arise from reverberation between the near and far walls of a small metallic or calcified reflector, producing a bright tapering trail of echoes distal to the focus.
CCI Ultrasound Physics and Instrumentation 5
The mechanical index (MI) displayed on an ultrasound machine is most closely associated with the risk of: