Ultrasound Physics & Doppler Principles Flashcards

The resistive index (RI) is calculated as:

Answer: (PSV - EDV) / PSV

RI = (PSV − EDV) / PSV; it reflects downstream vascular resistance, with values approaching 1.0 indicating high resistance.

Which Doppler waveform characteristic is most consistent with a high-resistance peripheral arterial bed at rest?

Answer: Triphasic waveform with brief reverse flow component

Normal resting peripheral arteries (e.g., femoral) show a triphasic waveform with a brief reverse-flow component in early diastole reflecting high resistance.

Aliasing on color Doppler is recognized by:

Answer: An abrupt transition from one color to the opposite color (color reversal)

Aliasing appears as an abrupt wrap-around from the maximum positive color to the maximum negative color (or vice versa) when velocities exceed the Nyquist limit.

Increasing transducer frequency improves axial resolution because:

Answer: Wavelength decreases, allowing shorter spatial pulse length

Higher frequency produces shorter wavelengths, enabling shorter spatial pulse lengths and finer axial resolution.

The pulsatility index (PI) differs from the resistive index in that PI:

Answer: Can exceed 1.0, whereas RI cannot

PI = (PSV − MDV) / mean velocity and can be greater than 1.0 in high-resistance vessels, while RI is bounded between 0 and 1.

Which mode of Doppler allows simultaneous real-time B-mode imaging and spectral Doppler acquisition without compromising either?

Answer: Duplex mode

Duplex mode combines B-mode imaging with pulsed-wave Doppler, though full triplex (adding color) requires more processing resources.

What happens to the Doppler frequency shift if the transducer frequency is doubled while all other parameters remain constant?

Answer: It doubles

The Doppler equation shows fd is directly proportional to the transmitted frequency (ft), so doubling ft doubles the Doppler shift.