Velocity measurements with a new ultrasonic Doppler method independent of angle of incidence.

Blood flow velocity measured by Doppler ultrasound is the relative velocity dependent on the path of the ultrasound beam, which should be influenced by its angle of incidence against the blood flow in the vessel. The angle of incidence generates varying changes in flow velocities that can be measured by the Doppler device. The aim of our study was to develop a new ultrasonic Doppler catheter which could provide a true flow velocity independently of the angle of the ultrasound beam against the flow direction, and to assess the validity of the true flow velocity obtained by a new device using the electromagnetic flowmeter. The newly developed Doppler catheter has a pair of adjoining ultrasonic crystals located on one side of the catheter at right angles to each other. Each Doppler shift, which is detected by two transducers (Δf1, Δf2) that sample the flow velocity at two closely spaced points, is used to compute two velocity measurements (V1 and V2); these are the velocities detected by the transducers. The true velocity was calculated using the following equation: V=((V1)2+(V2)2)1/2, where V = true velocity. The velocities were calculated by newly developed phase differential techniques. Using a continuous flow model, we compared the flow velocity measured by the new Doppler catheter with that assessed by an electromagnetic flow probe placed into the circuit. At between 0.42 and 4.49 l·min-1, the flow velocity measured by the new Doppler catheter (Doppler velocity) at five sampling depths was compared with the mean velocity calculated from the volumetric flow rate measured by an electromagnetic flowmeter (EMF velocity). The Doppler velocity (y) strongly correlated with the EMF velocity (x) at five sampling depths (r 2=0.99, respectively). At the maximal velocity sampling depth, the regression equation was y=1.29x+2.47 (r 2=0.99,P<0.0001,n=41, SEE=0.015). The Doppler velocity also correlated with the volumetric flow rate measured by the electromagnetic flowmeter (r 2=0.99). The flow velocity measurements using the new Doppler catheter and device we have developed can provide more instantaneous and useful information on hemodynamics.