Ultrasound Physics and Instrumentation Flashcards

Which of the following best describes the duty factor in pulsed ultrasound?

Answer: The ratio of pulse duration to the pulse repetition period

Duty factor is the fraction of time the transducer is actively transmitting, calculated as pulse duration divided by the pulse repetition period.

The spectral broadening seen in Doppler waveforms from a stenotic vessel is primarily caused by:

Answer: Turbulent flow creating a wide range of velocities within the sample volume

Turbulence disorganizes flow so that red blood cells move at many different velocities simultaneously, filling in the spectral window and causing spectral broadening.

Which AIUM/NEMA safety index estimates the likelihood of cavitation in tissue?

Answer: Mechanical index (MI)

The Mechanical Index (MI = peak negative pressure / √frequency) estimates the potential for cavitation, with values above 0.3 suggesting increased risk.

In the context of Doppler ultrasound, the angle of insonation should ideally be kept at or below:

Answer: 60 degrees

Doppler angle correction is most accurate when the angle is ≤60°; beyond 60° the cosine function changes rapidly, introducing large velocity measurement errors.

A hypoechoic structure on ultrasound indicates that it:

Answer: Reflects fewer echoes than surrounding tissue

Hypoechoic means the structure appears darker (fewer/lower amplitude echoes) compared to adjacent tissue, not completely echo-free.

Which parameter, when increased, will reduce the maximum depth from which unambiguous pulsed Doppler signals can be obtained?

Answer: Pulse repetition frequency (PRF)

Higher PRF reduces the time between pulses, meaning echoes from deep structures may return after the next pulse is fired, causing range ambiguity.

The phenomenon where sound bends as it crosses a boundary between tissues of different propagation speeds is called:

Answer: Refraction

Refraction occurs at tissue interfaces where propagation speed differs, causing the beam to change direction and potentially producing misregistration artifacts.