ARDMS SPI Image Formation and Processing 4 — Questions and Answers
Question 1: Tissue harmonic imaging improves image quality primarily by:
- Increasing the transmit frequency beyond the transducer's rated bandwidth
- Using the second harmonic frequency generated within tissue to form the image (Correct answer)
- Doubling the pulse repetition frequency
- Applying a band-pass filter centered on the fundamental frequency
Correct answer: Using the second harmonic frequency generated within tissue to form the image
As sound propagates through tissue, nonlinear distortion generates harmonic frequencies; imaging at the second harmonic reduces near-field artifact and clutter because harmonics build up away from the transducer.
Question 2: Dynamic range in ultrasound refers to:
- The range of depths over which the system can focus
- The ratio of the largest to smallest echo amplitudes the system can process and display (Correct answer)
- The bandwidth of frequencies included in the transmit pulse
- The maximum frame rate achievable at a given depth
Correct answer: The ratio of the largest to smallest echo amplitudes the system can process and display
Dynamic range (expressed in dB) describes the span between the strongest and weakest signals that can be meaningfully represented, influencing the number of displayed gray levels.
Question 3: Increasing the dynamic range setting on the ultrasound unit will:
- Narrow the range of displayed gray levels
- Produce a higher contrast image with fewer gray shades
- Display more gray shades, producing a softer-appearing image (Correct answer)
- Increase the transmit power to deeper structures
Correct answer: Display more gray shades, producing a softer-appearing image
A wider displayed dynamic range maps more levels of echo amplitude into the gray scale, resulting in more subtle gray-scale gradations and a lower-contrast appearance.
Question 4: Compound spatial imaging (multi-angle compounding) improves image quality by:
- Firing multiple pulses at different frequencies simultaneously
- Averaging images acquired from several steering angles to reduce speckle and improve margin definition (Correct answer)
- Increasing pulse repetition frequency to improve frame rate
- Using coded excitation to penetrate deeper structures
Correct answer: Averaging images acquired from several steering angles to reduce speckle and improve margin definition
By combining frames obtained at different steering angles, compound imaging reduces angle-dependent artifacts and averages out speckle, improving structural border visibility.
Question 5: Coded excitation in ultrasound systems is used primarily to:
- Increase lateral resolution at shallow depths
- Improve signal-to-noise ratio and penetration without increasing peak pressure (Correct answer)
- Reduce the pulse repetition interval
- Eliminate grating-lobe artifacts from phased arrays
Correct answer: Improve signal-to-noise ratio and penetration without increasing peak pressure
Coded excitation (e.g., chirp or Golay codes) spreads pulse energy over time and uses matched-filter compression on receive, boosting SNR and penetration at the same mechanical index.
Question 6: Persistence (frame averaging) in ultrasound imaging reduces noise by:
- Increasing the transmit power for each individual frame
- Averaging multiple successive frames to smooth random variations (Correct answer)
- Widening the receive bandwidth of the transducer
- Applying a high-pass filter to each scan line
Correct answer: Averaging multiple successive frames to smooth random variations
Temporal averaging (persistence) blends consecutive frames; random speckle averages toward zero while real persistent structures remain visible.
Question 7: Which processing technique maps the received echo amplitude non-linearly to compress the wide dynamic range of tissue echoes into a displayable gray scale?
- Time-gain compensation
- Log compression (Correct answer)
- Demodulation
- Envelope detection
Correct answer: Log compression
Log compression applies a logarithmic transfer function to the echo amplitudes, compressing the large dynamic range of returning signals into the narrower range the display can show.
ARDMS SPI Image Formation and Processing 4
Tissue harmonic imaging improves image quality primarily by: