A polydisperse scattering model adapted for concentrated medium, namely the polydisperse structure factor model, was examined in order to explain the backscatter coefficients (BSCs) measured from packed cell samples undergoing cell death. Cell samples were scanned using high-frequency ultrasound in the 10-42 MHz bandwidth. A parameter estimation procedure was proposed in order to estimate the volume fraction and the relative impedance contrast that could explain the changes in BSC pattern by considering the actual change in cellular size distribution. Quantitative ultrasound parameters were estimated and related to the percentage of dead cells determined by flow cytometry. The standard deviation of scatterer size distribution extracted from the polydisperse structure factor model and the spectral intercept were found to be strongly correlated to the percentage of dead cells (r^2 =0.79 and r^2 =0.72, respectively). The current study contributes to the understanding of ultrasonic scattering from cells undergoing cell death toward the monitoring of cancer therapy.