CCI Ultrasound Physics and Instrumentation 2 — Questions and Answers
Question 1: Which property of ultrasound determines the maximum depth of penetration in tissue?
- Frequency (Correct answer)
- Amplitude
- Wavelength
- Pulse repetition frequency
Correct answer: Frequency
Lower frequencies penetrate deeper because attenuation increases with frequency, so lower frequencies lose less energy per unit depth.
Question 2: The term 'acoustic impedance' is defined as the product of:
- Frequency and wavelength
- Density and propagation velocity (Correct answer)
- Amplitude and frequency
- Attenuation and depth
Correct answer: Density and propagation velocity
Acoustic impedance (Z) equals tissue density (ρ) multiplied by the speed of sound (c) in that medium, expressed as Z = ρc.
Question 3: What artifact occurs when a strong reflector causes repeated echo returns at equally spaced intervals?
- Side lobe artifact
- Acoustic shadowing
- Reverberation artifact (Correct answer)
- Mirror image artifact
Correct answer: Reverberation artifact
Reverberation artifacts occur when sound bounces repeatedly between two strong reflectors, creating equally spaced false echoes at multiples of the true depth.
Question 4: In pulsed wave Doppler, the Nyquist limit determines the maximum:
- Depth that can be sampled
- Velocity that can be accurately measured without aliasing (Correct answer)
- Frame rate achievable
- Pulse duration used
Correct answer: Velocity that can be accurately measured without aliasing
The Nyquist limit is half the pulse repetition frequency; velocities causing Doppler shifts exceeding this value will alias and display incorrectly.
Question 5: Which mode of echocardiography provides the highest temporal resolution for cardiac motion analysis?
- 2D imaging
- M-mode (Correct answer)
- Color flow Doppler
- 3D echocardiography
Correct answer: M-mode
M-mode records a single line of information at a very high frame rate (typically 1,000 frames/sec), providing superior temporal resolution for cardiac motion.
Question 6: The speed of sound in soft tissue is approximately:
- 340 m/s
- 1,540 m/s (Correct answer)
- 3,500 m/s
- 330 m/s
Correct answer: 1,540 m/s
Ultrasound machines assume a constant propagation speed of 1,540 m/s in soft tissue to calculate depth from echo return time.
Question 7: Harmonic imaging improves image quality primarily by:
- Increasing transmitted frequency
- Reducing side lobe and reverberation artifacts (Correct answer)
- Increasing pulse repetition frequency
- Widening the beam width
Correct answer: Reducing side lobe and reverberation artifacts
Tissue harmonic imaging uses the second harmonic frequency generated within tissue, which has a narrower beam and fewer near-field artifacts than the fundamental frequency.
CCI Ultrasound Physics and Instrumentation 2
Which property of ultrasound determines the maximum depth of penetration in tissue?