Surface integration of velocity vectors from 3D digital colour doppler: An angle independent method for laminar flow measurements

Background: The study was designed to test the angle independence of a dynamic three-dimensional digital colour Doppler method for laminar flow measurement. The technique acquired three-dimensional data by rotational acquisition and used surface integration of Doppler vector velocities and flow areas in time and space for flow computation. Method: A series of pulsatile flows (peak flow 55-180 ml/s) through a curved tube were studied with reference flow rates obtained using an ultrasonic flow meter. Colour Doppler imaging was performed at three angles to the direction of flow (20°, 30°, 40°), using a multiplane transoesophageal probe controlled by an ATL HDI 5000 system. Integration of digital velocity vectors over a curved three-dimensional surface across the tube for each of the 11 flow rates at each angle was performed off-line to compute peak flow. Results: Peak flow rates correlated closely (r=0.99) with the flow meter with the mean difference from the reference being -0.8 ± 2.4 ml/s, 0.9 ± 2.6 ml/s, 1.0 ± 2.3 ml/s for 20°, 30° and 40° respectively. Comparison of the three angle groups showed no significant differences (P=0.15, ANOVA). When sampled obliquely, the flow area on the curved surface increased while the velocities measured decreased. Conclusion: Surface integration of velocity vectors to compute three-dimensional Doppler flow data is less angle dependent than conventional Doppler methods.