Monitoring structural changes in cells with high-frequency ultrasound signal statistics

We investigate the use of signal envelope statistics to monitor and quantify structural changes during cell death using an in vitro cell model. Using a f/2.35 transducer (center frequency 20 MHz), ultrasound backscatter data were obtained from pellets of acute myeloid leukemia cells treated with a DNA-intercolating chemotherapy drug, as well as from pellets formed with mixtures of treated and untreated cells. Simulations of signals from pellets of mixtures of cells were generated as a summation of point scatterers. The signal envelope statistics were examined by fitting the Rayleigh and generalized gamma distributions. The fit parameters of the generalized gamma distribution showed sensitivity to structural changes in the cells. The scale parameter showed a 200% increase (p<0.05) between untreated and cells treated for 24 h. The shape parameter showed a 50% increase (p<0.05) over 24 h. Experimental results showed reasonable agreement with simulations. The results indicate that high-frequency ultrasound signal statistics can be used to monitor structural changes within a very low percentage of treated cells in a population, raising the possibility of using this technique in vivo.