Effect of Velocity Profile Skewing on Blood Velocity and Volume Flow Waveforms Derived From Maximum Doppler Spectral Velocity

Given evidence that fully developed axisymmetric flow may be the exception rather than the rule, even in nominally straight arteries, maximum velocity (V_max) can lie outside the Doppler sample volume (SV). The link between V_max and derived quantities, such as volume flow (Q), may therefore be more complex than commonly thought. We performed idealized virtual Doppler ultrasound on data from image-based computational fluid dynamics (CFD) models of the normal human carotid artery and investigated how velocity profile skewing and choice of sample volume affected V_max waveforms and derived Q variables, considering common assumptions about velocity profile shape (i.e., Poiseuille or Womersley). Severe velocity profile skewing caused substantial errors in V_max waveforms when using a small, centered SV, although peak V_max was reliably detected; errors with a long SV covering the vessel diameter were orientation dependent but lower overall. Cycle-averaged Q calculated from V_max was typically within ±15%, although substantial skewing and use of a small SV caused 10%–25% underestimation. Peak Q derived from Womersley's theory was generally accurate to within ±10%. V_max pulsatility and resistance indexes differed from Q-based values, although the Q-based resistance index could be predicted reliably. Skewing introduced significant error into V_max-derived Q waveforms, particularly during mid-to-late systole. Our findings suggest that errors in the V_max and Q waveforms related to velocity profile skewing and use of a small SV, or orientation-dependent errors for a long SV, could limit their use in wave analysis or for constructing characteristic or patient-specific flow boundary conditions for model studies.