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-mo de imaging (7 MHz) was used to measure simultaneously the echogenicity and velocity profiles of 28% hematocrit porcine whole blood. Measurem ents were made at various axial locations in a large diameter (D = 2.5 4 cm) long (> GOD) tube, under steady flow conditions. A block matchin g (correlation) technique between successive digitized images was used to determine the velocity profiles, and from these, shear rate profil es were calculated. The optimal block dimensions were found to be depe ndent on the magnitude and direction of the flow shear rate. Echogenic ity profiles were determined from ensemble averaged images. It is show n how such profiles in combination with the corresponding shear rate p rofiles enables information to be obtained concerning the dependence o f aggregation on shear rate. Pulsed Doppler ultrasound (20 MHz) was al so 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 m agnetic resonance imaging and mean velocity errors of less that 5% wer e achieved.