Image Formation and Processing Flashcards

Tissue harmonic imaging improves image quality primarily by:

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.

Dynamic range in ultrasound refers to:

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.

Increasing the dynamic range setting on the ultrasound unit will:

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.

Compound spatial imaging (multi-angle compounding) improves image quality by:

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.

Coded excitation in ultrasound systems is used primarily to:

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.

Persistence (frame averaging) in ultrasound imaging reduces noise by:

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.

Which processing technique maps the received echo amplitude non-linearly to compress the wide dynamic range of tissue echoes into a displayable gray scale?

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.