In vitro hemolysis using a switched spiral focal field

An efficient method of ultrasound irradiation to induce biologically effective cavitation is presented. A sector-vortex transducer, a phased array transducer with multiple sectors and a geometric focus, is used to produce ultrasound focal fields with spirally shaped wavefronts. Clockwise and counterclockwise spiral focal fields with basically the same ultrasound power distribution but having different wavefront angles are produced by using the same array transducer. The in vitro bioeffects from the periodic switching between such a pair of spiral focal fields are investigated. Suspended rat erythrocytes were insonated for 1 min at an ultrasound frequency of 750 kHz. A significantly high hemolysis rate is observed at a switching period of 10 ms. The rate is about ten times higher than those at switching periods of 0.1 ms or 1 s. Similar switching period dependence is also seen in the enhancement of hemolysis by adding sonochemical sensitizers