VT Ultrasound Physics & Doppler Principles 2

Question 1

What phenomenon occurs when the ultrasound beam strikes a smooth, flat interface larger than the wavelength?

Accepted Answer

Specular reflection

Answer

Specular reflection occurs at large, smooth interfaces where the beam reflects at an angle equal to the angle of incidence.

Question 2

The Nyquist limit in pulsed-wave Doppler is equal to:

Accepted Answer

One-half the pulse repetition frequency

Answer

The Nyquist limit equals PRF/2; velocities exceeding this cause aliasing in pulsed-wave Doppler.

Question 3

Which parameter most directly controls the depth of penetration of an ultrasound beam?

Accepted Answer

Frequency

Answer

Lower frequencies penetrate deeper because they are attenuated less per centimeter of tissue.

Question 4

In continuous-wave Doppler, which limitation does NOT apply?

Accepted Answer

Nyquist limit

Answer

CW Doppler has no PRF, so there is no Nyquist limit and it can detect very high velocities without aliasing.

Question 5

Acoustic impedance (Z) is defined as the product of:

Accepted Answer

Density and propagation speed

Answer

Z = ρ × c, where ρ is tissue density and c is the speed of sound in that medium.

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