Quantitative ultrasound imaging of bacterial infection on skin ulcers by envelope statistics analysis

We aim to characterize tissues of skin ulcers for bacterial infection quantitatively. The echo amplitude envelope of the backscattered signals can be described by some statistics distributions in consistent with the different scattering. The basic statistics distributions (Rayleigh, K, and Rician distributions) were used to detect the difference of backscattered signals between non-infected and infected tissue. Three kinds of animal skin ulcer models (non-infection, colonization, and infection models) with open injury in rats were characterized in this study. Ultrasound data were acquired by modified ultrasonic diagnostic equipment with a linear phased array transducer. The center frequency of a linear phased array ultrasound transducer was 8.9 MHz. In addition to animal models study, we simulated the echo signal from random scatterer mediums to confirm the relationship between variation of quantitative ultrasound (QUS) parameters and scatterer structure. As QUS parameters, the ratio of the mean to standard deviation of the echo amplitude envelope and the statistics distribution parameter were computed in each analysis. In the infection model rat, the typical difference of statistics distribution parameters (non-Rayleigh or Rayleigh distribution parameter) corresponding to the observed histopathological difference are shown in noninfected and infected tissues. Additionally, this tendency are described in 2D analysis of each model rat. From the result of computer simulation, scatterer number density is correlated with QUS parameters, and assumes to be also influenced by the histopathological structure in animal models whether infected or not.