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 sound speed and density of the object and the surrounding fluid, respectively. 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 200 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 sound speed from single cells found to vary between 1540 to 1580 m/s when the density was fixed at 1050 kg/m3.