To measure end-diastolic velocity, which adjustment should be performed?

• A. Lower wall filter
• B. Increase PRF
• C. Decrease angle of incidence
• D. Lower zero baseline

Answer: (A)

End-diastolic velocity is a very slow component of blood flow, so detecting it requires that the system pass through the slow Doppler shifts without suppressing them. The wall filter acts as a high-pass filter that removes low-frequency signals, which are often tissue motion or very slow flow. If the wall filter is too aggressive, those slow Doppler shifts from end-diastolic flow get filtered out, making it hard or impossible to see the end-diastolic velocity on the spectrum. Lowering the wall filter reduces that cutoff, letting the slow flow signals appear clearly.

Other adjustments don’t specifically improve the visibility of slow velocity signals. Increasing the pulse repetition frequency expands the measurable velocity range and helps with aliasing, but doesn’t address the detection of low-velocity diastolic flow. Decreasing the angle of incidence improves velocity accuracy relative to the beam but won’t reveal a signal that the filter has already suppressed. Lowering the zero baseline shifts the display baseline but doesn’t enhance the presence of slow flow.