An innovative synthetic tissue-mimicking material for high-intensity focused ultrasound

Abstract

A dosimetry study of the high-temperature and pressure regimes involved in high-intensity focused ultrasound (HIFU) requires experiments on biological tissues because no synthetic tissue-mimicking phantom is available. Unfortunately, the development of coagulative lesions cannot be observed in real-time in opaque tissues. Furthermore, the natural heterogeneous structure of tissue complicates direct comparison with numerical models. In this study, a new optically transparent phantom is evaluated. It is principally composed of a polyacrylamide gel, and includes a thermally sensitive indicator protein that becomes optically diffusive when denatured. Various tests were undertaken to characterize the acoustical, thermal, and optical properties of this material for a range of protein concentrations. The attenuation coefficient can be usefully modified by adjusting the quantity of embedded proteins to permit some selection of acoustic regime. It is also possible to emphasize cavitation activity at lower BSA concentrations, or thermal effects at higher concentrations. This new phantom adequately matches tissue for most of the measured parameters and facilitates the study of the HIFU bioeffects. [Work supported by ONR Grant No. N00014-96-1-0630 and NIH Grant No. HL64208-02.]