A simulation study on ultrasound backscattering by cell aggregates with poly-disperse cells

A Monte Carlo simulation study on ultrasound backscattering by cell aggregates with poly-disperse cells is discussed. The nuclei in a cell aggregate were assumed as scatterers and the Anderson model was used to obtain backscattering amplitude for each nucleus. The resultant backscatter echo from many particles was determined by using linear superposition of backscatter signals emitted by the nuclei. The random sequential adsorption (RSA) method was employed to generate spatial organizations of nuclei. The frequency dependent backscattering coefficient (BSC) and signal envelope statistics were obtained from tissue samples with different size distributions. For each poly-disperse sample the nuclear populations followed a Gaussian distribution with the nuclear packing fraction fixed at 50.36%. It was found that integrated backscattering coefficient (IBSC) computed between 10-30 MHz increased about 7 dB for the highest poly-disperse sample considered compared to that of a mono-disperse sample. A Gaussian input pulse was employed to investigate signal envelope statistics. It was found that envelope histograms followed the Rayleigh distribution. The Rayleigh fit parameter (σ) increased as dispersity increased. For example, for the highest poly-disperse sample, σ increased about 105% and 157% compared to mono-disperse sample for input pulses with 5 and 25 MHz as the center frequencies and 80% bandwidths. The present work shows that poly-dispersity contributes to ultrasound backscatter but the shapes of histograms did not vary with the size distribution of scatterers.