With PISA, the aliasing velocity is commonly set at which range?

• A. 20-40 cm/s
• B. 5-10 cm/s
• C. 60-80 cm/s
• D. 100-120 cm/s

Answer: (A)

In PISA, the aliasing velocity (Nyquist limit) sets the velocity at which color Doppler wraps around to form the isovelocity shell around the regurgitant orifice. Setting this value to a moderate range, about 20–40 cm/s, provides a measurable hemispherical shell whose radius can be accurately traced in the image. That radius is then used to estimate flow (Q ≈ 2π r^2 × V_alias) and, with the jet velocity, to derive the regurgitant severity.

If the aliasing velocity were too high, the PISA radius would shrink too much, making the measured radius sensitive to small errors and potentially underestimating flow. If it were too low, the radius would expand too large and could exceed the imaging window or be less reliable due to lower resolution and angle effects. The 20–40 cm/s range hits a balance, giving a practical, reproducible radius for accurate calculations.