Estimation of hematocrit by means of dual-gate power Doppler

Noninvasive estimation of the blood hematocrit is important for medical diagnosis. At present, there is only one reliable method based on measurement of speed of sound. It is mainly used during patient´s dialysis. We propose a novel approach to solve this problem. The instrumentation developed is based on the dependence of the absorption of an ultrasonic wave in blood. The instrument is based on a pulsed Doppler ultrasonic blood flowmeter, operating at frequency 20 MHz. The Doppler signal is simultaneously recorded in two gates at two distinct depths. The ratio of signal power from two gates depends on hematocrit only. The preliminary measurements were done in vitro using porcine blood. The Doppler signal was recorded in two gates separated by 1.2 mm and 3.6 mm. A good agreement between hematocrit values calculated from the Doppler signal and laboratory measurements was obtained: for sample volumes separated by 3.6 mm correlation coefficients were equal to 0.96 for p<0.001. This novel method offers the possibility of direct monitoring of hematocrit during dialysis