Ultrasound methods for investigating the non-Newtonian characteristics of whole blood

The development and evaluation of new techniques for investigating the non-Newtonian characteristics of blood are described. Ultrasound B-mode imaging (7 MHz) was used to measure simultaneously the echogenicity and velocity profiles of 28% hematocrit porcine whole blood. Measurements were made at various locations in a large diameter (D=2.54 cm) long (>60 D) tube, under steady flow conditions. A block matching (correlation) technique between successive digitized images was used to determine the velocity profiles, and from these, shear rate profiles were calculated. The optimal block dimensions were found to be dependent on the magnitude and direction of the flow shear rate. Echogenicity profiles were determined from ensemble averaged images. It is shown how such profiles in combination with the corresponding shear rate profiles enables information to be obtained concerning the dependence of aggregation on shear rate. Pulsed Doppler ultrasound (20 MHz) was also used to measure the velocity and backscattered power profiles at 60 D from the tube entrance. Velocity profiles measured using B-mode were in good agreement with those obtained using both pulsed Doppler and magnetic resonance imaging and mean velocity errors of less that 5% were achieved.<
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