Ultrasonic spectrum analysis for tissue assays and therapy evaluation

Ultrasonic spectrum analysis procedures have been developed to measure tissue morphologic features that are not well depicted with conventional ultrasonography. This article reviews some of the applications of spectral techniques and provides an expanded theoretical framework showing how measured spectral features are related to the spatial autocorrelation function descriptive of tissue microstructure. Explicit relationships are obtained that describe how linear-regression spectral parameters are related to the effective mean sizes, concentrations, and relative mechanical properties of scattering centers in tissue. In vitro, in vivo, and clinical results are presented illustrating how these techniques can be used to evaluate tissue alterations induced by ultrasonic hyperthermia and ablative treatments of tumors. These results show that ultrasonic spectrum analysis can provide quantitative information regarding changes in microstructure attributes. Spectral parameter images in two and three dimensions demonstrate how such procedures can map the spatial extent and severity of these changes, thereby providing a quantitative basis for assessing the results of tumor therapy.