STATISTICAL PROPERTIES OF ESTIMATES OF SIGNAL-TO-NOISE RATIO AND NUMBER OF SCATTERERS PER RESOLUTION CELL

Elementary theory underlying the relationship between the number of sc atterers per resolution cell (N) and echo intensity signal-to-noise ra tio (SNR) is reviewed. A relationship between the probability density functions for estimates of N and SNR2 is derived. This relationship is validated using a computer simulation Phantom and in vitro experiment s are described. In one set of experiments on phantoms, empirical dist ributions of estimates of N and SNR2 are measured and compared to theo retical predictions. The utility of SNR2 for discrimination of phantom s with different values for N is assessed using receiver operating cha racteristic (ROC) analysis. In another set of experiments, the frequen cy dependence of the SNR2 estimate is investigated for a two-component phantom and for excised dog kidney. It is shown that the frequency de pendence of the SNR can help to identify the presence of two or more s cattering components that are spatially mixed. With regard to kidney d ata, measurements performed both parallel and perpendicular to the pre dominant nephron orientation are reported. The observed anisotropy is compared to the anisotropy of backscatter coefficient encountered in p revious investigations.