Quantitative particle characterization by ultrasound

Abstract

An acoustic scattering technique was developed for determining the compressibility and density of microparticles (diameter less than 15 μm), which were modeled as fluid spheres. Tone bursts of 2-μs duration and 30-MHz center frequency were scattered from individual microparticles as they traversed the confocal region of two transducers. The scattered bursts were detected at 90° and 180° (backscattering), digitized, and stored in computer memory. By using either the Rayleigh or Born approximations, it was possible to determine the compressibility and density of the particles given a priori knowledge of the particle size and host properties. It was subsequently possible to compute the mean compressibility and density averaged over a population of particles, or to display histograms of scattered amplitude statistics. An experiment was run to assess the feasibility of using polystyrene microspheres to calibrate the instrument. A second study was performed on the buffy coat harvested from whole human blood. Finally, Chinese hamster ovary cells were studied in order to see if the instrument could detect hyperthermia induced membrane blistering. [Work supported by NIH and ONP.]