Spectral Doppler Waveform Analysis Flashcards

Increasing the sample volume (gate) size in spectral Doppler will most likely:

Answer: Include more of the vessel lumen and potentially increase spectral broadening

A larger sample volume captures flow across more of the vessel cross-section, including slower cells near the vessel walls, which introduces a wider range of velocities and increases spectral broadening.

The systolic-to-diastolic (S/D) ratio used in obstetric Doppler is calculated as:

Answer: PSV / EDV

The S/D ratio = PSV / EDV and is commonly used in umbilical artery Doppler to assess placental resistance; it cannot be calculated when EDV is absent.

When PRF is increased to correct aliasing, which undesirable consequence may occur?

Answer: Range ambiguity — inability to unambiguously sample deep vessels

High PRF sends pulses before previous echoes return from deep structures, so the system cannot determine which echo came from which pulse depth, creating range ambiguity artifact.

Baseline shifting in spectral Doppler is primarily used to:

Answer: Reposition the zero-velocity line to allocate more display range to unidirectional flow

Shifting the baseline moves the zero-velocity reference line, allowing more of the display to be used for flow in one direction before aliasing wraps the signal to the other side.

Compared to pulsed-wave (PW) Doppler, which statement about continuous-wave (CW) Doppler is TRUE?

Answer: CW has no Nyquist limit and can measure very high velocities without aliasing

CW Doppler continuously transmits and receives simultaneously; because it does not use pulsed sampling, it has no PRF and therefore no Nyquist limit, allowing measurement of very high velocities — at the cost of range discrimination.

A spectral Doppler waveform displaying a mirror image of the true waveform simultaneously on both sides of the baseline is most likely caused by:

Answer: Doppler gain set too high, causing cross-talk (ghosting) artifact

Cross-talk (ghosting or mirror image artifact) in spectral Doppler occurs when the Doppler gain is set too high, causing the waveform signal to bleed through to the opposite side of the baseline.

The time-averaged mean velocity (TAMV) is the denominator used to calculate which Doppler index?

Answer: Pulsatility Index (PI)

The Pulsatility Index = (PSV - EDV) / TAMV; it is the only common index using the mean velocity as the denominator, making it calculable even when end-diastolic flow is zero or reversed.