Validation of Transverse Oscillation Vector Velocity Estimation In-Vivo

Conventional Doppler methods for blood velocity estimation only estimate the velocity component along the ultrasound (US) beam direction. This implies that a Doppler angle under examination close to 90deg results in unreliable information about the true blood direction and blood velocity. The novel method Transverse Oscillation (TO), which combines estimates of the axial and the transverse velocity components in the scan plane, makes it possible to estimate the vector velocity of the blood regardless of the Doppler angle. The present study evaluates the TO method with magnetic resonance angiography (MRA) by comparing in-vivo measurements of stroke volume (SV) obtained from the right common carotid artery. Angle of insonation was 90deg for the TO measurements. Eleven healthy volunteers were scanned with the TO method and MRA. The overall results were as follows: mean SV +/- STD for TO: 5.5 ml +/- 1.7 ml and for MRA: 5.8 ml +/- 2.0 ml with the full range for TO: 3.4 ml - 9.5 ml and for MRA 3.0 ml - 10.8 ml. The correlation between the SV estimated by TO and MRA was 0.91 (p < 0.01; 95 % CI: 0.69 to 0.98) with the equation for the line of regression MRA = 1.1ldrTO - 0.4. A Bland-Altman plot was constructed where the mean difference was 0.2 ml with limits of agreement at -1.4 ml and 1.9 ml (95 % CI for mean difference: -0.3 ml to 0.8 ml). The strong correlation and the low mean difference between the TO method and MRA indicates that reliable vector velocity estimates can be obtained in vivo using the presented angle independent 2-D vector velocity method. The results give reason to believe that the TO method can be a useful alternative to conventional Doppler systems bringing forth new information to the US examination of blood flow.