Ultrasound Physics and Instrumentation Flashcards

Acoustic shadowing distal to a calcified vessel wall is caused by:

Answer: High reflection and absorption at the calcified interface preventing sound transmission

Calcifications have high acoustic impedance and absorb/reflect most incident sound energy, leaving little to penetrate further and creating a shadow behind the calcification.

A mirror image artifact in Doppler ultrasound refers to:

Answer: A duplicate spectral waveform appearing on the opposite side of the baseline

Doppler mirror image artifact creates a duplicate spectral waveform below the baseline that mimics reversed flow; it results from excessive gain or strong specular reflectors redirecting sound.

Harmonic imaging improves image quality primarily by:

Answer: Using second-harmonic frequencies generated within tissue to reduce near-field clutter and side-lobe artifacts

Tissue harmonic imaging receives echoes at twice the transmitted (fundamental) frequency; because harmonics build up within tissue rather than at the transducer surface, near-field artifact and clutter are greatly reduced.

Lateral resolution in ultrasound imaging is best at the:

Answer: Focal zone of the transducer

Lateral resolution (ability to separate two side-by-side structures) is optimal at the focal zone where the beam is narrowest, and degrades in both the near and far fields as the beam diverges.

The ALARA principle in diagnostic ultrasound stands for:

Answer: As Low As Reasonably Achievable

ALARA (As Low As Reasonably Achievable) directs sonographers to use the lowest acoustic output necessary to obtain diagnostic images, minimizing potential bioeffects.

Reverberation artifact in ultrasound appears as:

Answer: Multiple equally spaced echoes distal to a highly reflective interface

Reverberation occurs when sound bounces repeatedly between two strong reflectors (or between a reflector and the transducer face), producing equally spaced artifactual lines at multiples of the reflector's depth.

Continuous-wave (CW) Doppler is preferred over pulsed-wave Doppler for measuring very high velocities because CW Doppler:

Answer: Has no Nyquist limit and therefore does not alias regardless of velocity

CW Doppler continuously transmits and receives on separate elements, so it has no pulse repetition frequency constraint and therefore no Nyquist limit, allowing measurement of very high velocities without aliasing.