| Popis: |
The direct measurement of the velocity profile of blood flowing in a vessel yields a volume flow estimate that is more accurate than single-point Doppler ultrasound. A volume flow estimate is made by assuming a circularly symmetric velocity field and integrating the velocity profile measured along a diameter. The many velocity measurements made contribute to higher precision in the integrated velocity estimate. Also, the velocity profile furnishes the functional diameter of the vessel at many points through the cardiac cycle. This algorithm, as implemented on the Philips CVI system, was tested theoretically by numerical modelling, and experimentally with a flow simulator. The effect of beamwidth, vessel size, and measurement position misalignment on the volume flow estimate were studied. Experimental and theoretical results agreed well and showed that the flow estimation algorithm can produce precise and accurate volume flow estimates. The flow estimate is sensitive to the flow angle and is inaccurate by 5% per degree error in the angle. Beamwidths of 1.0 to 1.5 mm are a good match to axial resolution and yield accurate volume flow estimates in vessels over 2 mm in diameter. Larger beamwidths give lower volume flow estimates, but are not as sensitive to misalignment. > |
