IN-VITRO MEASUREMENTS OF INERTIAL CAVITATION THRESHOLDS IN HUMAN BLOOD

Inertial cavitation thresholds were measured in human blood exposed to pulsed ultrasound. Freshly drawn blood, bank blood and aqueous diluti ons of both were used in this experimental study. Micrometer-sized pol ystyrene particles were used as extra potential nuclei in some samples . Focused transducers with megahertz center frequencies (2.5 MHz, 4.3 MHz) were employed to generate pulsed ultrasound to induce cavitation. Specially designed cells for hosting the blood samples were made to a dapt to the experimental environment, Cavitation threshold measurement s were achieved by using an active cavitation detection scheme which u tilizes a highly focused transducer with a much higher center frequenc y (30 MHz). In 50% diluted blood samples, when no polystyrene particle s were added to the samples, the threshold for cavitation was about 4. 1 MPa at 2.5 MHz, while no cavitation was detected at 4.3 MHz. General ly, the measured thresholds decrease in samples with lower volume conc entration of red blood cells or when polystyrene particles were added to the samples. Results show that the measured thresholds in some circ umstances are in the range of output pressure of diagnostic ultrasound instrumentation; but for whole, freshly drawn blood, our apparatus wa s unable to detect cavitation, even at 6.3 MPa.