Ultrasonic spectrum analysis procedures have been detissue features, which are not well characterized by conventional veloped to measure tissue morphologic features that are not well imaging.
depicted with conventional ultrasonography. This article reviews Ultrasound energy interacts with soft tissues in a diversity some of the applications of spectral techniques and provides an exof ways, and ultrasonic imaging is affected by phenomena not panded theoretical framework showing how measured spectral feaencountered to a significant degree with other medical imaging tures are related to the spatial autocorrelation function descriptive of modalities such as X radiation and magnetic resonance. Ultratissue microstructure. Explicit relationships are obtained that describe sonic imaging is more closely related to sonar, radar, and laser how linear-regression spectral parameters are related to the effective imaging technologies. Ultrasonic systems [1] employ short presmean sizes, concentrations, and relative mechanical properties of scattering centers in tissue. In vitro, in vivo, and clinical results are sure pulses, typically comprising two cycles of alternating compresented illustrating how these techniques can be used to evaluate pression and rarefaction with respect to ambient pressure; these tissue alterations induced by ultrasonic hyperthermia and ablative bipolar pulses are launched by focused transducers (or transducer treatments of tumors. These results show that ultrasonic spectrum arrays) usually operated at center frequencies near 5 MHz (0.3analysis can provide quantitative information regarding changes in mm wavelength). The pulses propagate relatively slowly (1.5 microstructure attributes. Spectral parameter images in two and three mm/ms) through soft tissues, where they are affected by diffracdimensions demonstrate how such procedures can map the spatial tion, acoustic attenuation, and refraction. Scattering occurs when extent and severity of these changes, thereby providing a quantitative a pulse encounters changes in the mechanical properties (density basis for assessing the results of tumor therapy. α§ 1997 John Wiley & and compressibility) of tissue constituents. Backscattered echo