In Vivo Sound Velocity in Reflection

Abstract

The measurement accuracy of sound velocity by reflection mode methods is estimated theoretically for the several v ersions of the technique suitable for in vivo application. Focal fields used in versions of the focus adjustment method (FAM) are analyzed b y computer simulation as well as the incoherent crossed-beam method (ICM) and the crossed-transmission-andreception-beam method (CTRM) for the same acoustic conditions. The results show that FAM with a large reception aperture, and both of the crossed-beam methods, produce identical v elocity measurement accuracies. Moreover, a new version of FAM with a modified synthetic aperture produces twice the accuracy of the other methods discussed. In vivo as well as in vitro sound velocity measurements have been made using a high-resolution scanner with pixel-by-pixel real-time dynamic focusing based on the FAM concept with a large reception aperture. Significant sound velocity differences have been detected in normal, cirrhotic, and fatty livers. Since the potential measurement accuracy of FAM is at least twice that of the t ested version, even better instrumentation for measurement of in vivo sound velocity is possible.