RVT Ultrasound Physics and Instrumentation 2

Question 1

The Doppler equation used to calculate flow velocity is: v = (f_d × c) / (2 × f_0 × cos θ). What does 'θ' represent?

Accepted Answer

The angle between the ultrasound beam and the direction of blood flow

Answer

θ is the Doppler angle—the angle between the insonating beam and the axis of blood flow; as θ approaches 90°, cos θ approaches 0 and velocity calculation becomes unreliable.

Question 2

Aliasing in color flow Doppler imaging appears as:

Accepted Answer

An abrupt color reversal in the center of a high-velocity jet

Answer

When peak Doppler shift exceeds the Nyquist limit, aliasing causes the color to wrap around and display the opposite color (e.g., red becomes blue) at the site of high velocity.

Question 3

Which technique is most effective for eliminating aliasing in pulsed-wave Doppler without switching to continuous-wave mode?

Accepted Answer

Increasing the pulse repetition frequency (PRF)

Answer

Increasing PRF raises the Nyquist limit (PRF/2), allowing higher Doppler shift frequencies to be sampled without aliasing.

Question 4

Power Doppler differs from conventional color flow Doppler primarily in that it displays:

Accepted Answer

The amplitude (power) of the Doppler signal rather than frequency shift

Answer

Power Doppler maps the intensity (energy) of the returning Doppler signal, making it more sensitive to slow flow and small vessels but providing no directional information.

Question 5

The range resolution (axial resolution) of a pulsed ultrasound system is primarily determined by:

Accepted Answer

Spatial pulse length

Answer

Axial resolution ≈ spatial pulse length / 2; shorter pulses (higher frequency, fewer cycles) improve the ability to distinguish two closely spaced reflectors along the beam axis.

(RVT) Registered Vascular Technologist Practice Test

(RVT) Registered Vascular Technologist Practice Test

RVT Ultrasound Physics and Instrumentation 2