Lawrence A. Crum
Appl. Phys. Lab., 1013 NE 40th St., Univ. of Washington, Seattle, WA 98105
Focus Surgery, Fremont, CA 94539
High-intensity focused ultrasound (HIFU) can be used to destroy tissue in vivo; recent applications of this modality to the treatment of benign prostatic hypertrophy (BPH) have met with significant success. The lesions formed by focused ultrasound can be induced by both thermal and mechanical (cavitation) mechanisms. However, the relative contributions of these two mechanisms, under varied HIFU parameters, are often difficult to ascertain. Descriptions are presented of some simple experiments designed to elucidate the relative roles of cavitation and thermal effects in specific tissues; these tests were undertaken in turkey breast tissues, but seem to correlate well with previous in vivo experiments in dogs and humans. The experiments indicate that cavitation, once induced, tends to shorten and broaden the thermally induced lesions, suggesting that the presence of free gas generated by the cavitation blocks passage of the ultrasound.