Sound speed estimation in single cells using the ultrasound backscatter power spectrum

Abstract

The acoustic properties of single cells such as their size, sound speed and attenuation are known to change depending on the type, state or disease progression of a cell. Typically ultrasonic pulse echo methods on adherent cells are used. We propose using the ultrasound backscatter power spectrum on cells in suspension to extract the acoustic parameters. When the ultrasound wavelength is on the same order as the dimensions of the cell, periodically varying minima and maxima occur throughout the power spectrum that depend on the size and sound speed of the object. The ultrasound parameters can be determined by comparing the measured spectrum to a theoretical scattering model. We measured the backscattered ultrasound signals from single MCF7 breast cancer cells in suspension using a 375 MHz transducer. The cell diameter was determined through simultaneous optical imaging. The sound speed was calculated by adjusting the parameters in the scattering model until a good fit of the spectral features between the model and measured agreed. The average sound speed from 16 cells found to vary between 1577 to 1611 m/s when the density was fixed at 1050 kg/m3.