The intensity dependence of the site of maximal energy deposition in focused ultrasound surgery

• Published in: Ultrasound in medicine & biology Vol. 22; no. 4; pp. 483 - 491
• Main Authors: Watkin, N.A., ter Haar, G.R., Rivens, I.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 1996; Elsevier
• Subjects: Abdomen; Absorption; Animals; Biological and medical sciences; Cattle; Cavitation; Computer Simulation; In Vitro Techniques; Liver Diseases - therapy; Male; Medical sciences; Miscellaneous; Models, Biological; Prostatic Neoplasms - therapy; Surgery; Surgery (general aspects). Transplantations, organ and tissue grafts. Graft diseases; Swine; Tissue ablation; Ultrasonic Therapy - methods; Ultrasound therapy; Urinary Bladder Neoplasms - therapy; Ultrasound therapy; Cavitation; Surgery; Tissue ablation; Human; Correlation; Spatial distribution; Position; Ultrasonic treatment; Tumor; Probe; Signal analysis
• ISSN: 0301-5629; 1879-291X
• DOI: 10.1016/0301-5629(95)02062-4

The relationship between spatial peak intensity and the position of ultrasound induced tissue damage was studied in in vitro tissue models, using a 1.69 MHz spherical bowl transducer. The models corresponded to the transabdominal route to the bladder and prostate, which are potential target sites for focused ultrasound surgery. The results confirm that there is a relationship between lesion position and intensity, with lesions forming, under some exposure conditions, ahead of the geometric focus. Forward growth of lesions appears to be due to changes in the absorption characteristics of the tissue in the beam path. Using a computer model, we have demonstrated that the absorption coefficient of the tissue must increase significantly in front of the focus to enable lesions to form ahead of the predicted position. A possible mechanism for this is bubble formation as a result of acoustic cavitation. The effect of nonlinear propagation in the tissue, at the intensities studied, is shown to be relatively small.