In vitro measurement of the vena contracta for stenotic valves using laser induced fluorescence imaging and digital particle image velocimetry: comparison with ultrasound Doppler

Effective orifice areas of stenotic valves are routinely estimated using ultrasound Doppler. However, several questions regarding the flow dependent nature of this technique have been raised. Using precise laser induced fluorescence (LIF) imaging and digital particle image velocimetry (DPIV), the authors were able to measure flow through the vena contracta region of stenotic orifices in vitro. LIF measured vena contracta areas were compared to Doppler areas as flow rate increased from 25 cc/sec to 165 cc/sec. Although actual vena contracta areas exhibited very little change as flow rate increased, Doppler measured areas showed a strong dependence on flow, especially at low flow rates. Doppler areas underestimated actual vena contracta areas significantly at low flows. DPIV measurements of the velocity profile at the vena contracta suggest that Doppler underestimation is due to a breakdown of the flat velocity profile assumption inherent in the Doppler method.