The broad goal of this work is to improve significantly the characterization and manipulation of biological materials using ultrasonic waves. 1. Primary project - Acoustic Scattering of Cell Characterization and Sorting. In our primary experiment, tone bursts of 30 MHz center frequency and 2 Mu-second duration scatter off of individual particles (red blood cells) as they pass through the focal region of three confocally positioned acoustic transducers. The scattered signal is detected at two angles (90 degrees and 135 degrees) and, with this information, we calculate the compressibility and density of the particles using long wavelength acoustic scattering theory. With the apparatus, as described, we have been able to plot histograms of the scattered acoustic intensity versus size or compressibility of red blood cells in host solutions of varying tonicity. We have also seen biomodal distributions in size for the case of rbc's from anemic patients, confirming our theoretical prediction that the intensity of ultrasound scattered in the 90 degree direction is proportional to the mean cellular hemoglobin content. We now plan a few important changes. By eliminating one of the receiving transducers and using the transmitter as a back-scatter receiver, we greatly simplify alignment problems. By processing signals in hardware, rather than software we increase the numbers of pulses that can be scattered off each cell, and we get information on each cell almost instantaneously thereby opening up a new possibility: that of cell sorting. 2. Secondary Project - Cell Manipulation and Deformation - We have been able to levitate acoustically small drops and biological cells in a specially designed chamber mounted on an optical microscope stage. We have been able to resonate the drops into shape oscillations, which provides information on the interfacial tension. We have been able to use this technique to produce drop fission. Although we have not been able to resonate biological cells, we have been able to statically deform sea urchin eggs. Our goal for continued work is to explore several possibilities for the acoustically-induced manipulation and deformation of biological cells. 3. Secondary Project - Characterization of the nonlinear property, B/A, of tissues using Phase-Locked Circuitry. By using a new, highly precise ultrasonic interferometer, we hope to be able to answer the question: Is the nonlinear parameter of tissues a useful measure for determining tissue pathology?
