Arterial blood flow occlusion by high intensity focused ultrasound and histologic evaluation of its effect on arteries and surrounding tissues.

High intensity focused ultrasound (HIFU) has been used in a number of clinical studies. High intensity focused ultrasound could become the minimally invasive tumor therapy of choice if it could be used to occlude the feeding arteries of tumors by exposure from outside the body. We used high intensity focused ultrasound to insonate the femoral arteries of both thighs of 18 male and female Sprague-Dawley (SD) rats, at frequencies of 1 or 3 MHz. Duration of exposure to high intensity focused ultrasound was 5 or 10 seconds. The femoral artery that was exposed to high intensity focused ultrasound was resected immediately after or 24 hours, 48 hours, or 12 days (at 1 MHz) after insonation. Arterial blood flow occlusion was achieved at 3 MHz, but not at 1 MHz. Free-field spatial peak intensity was 800 W/cm(2) at 1 MHz and 10 kW/cm(2) at 3 MHz. Histologic examination of the resected specimen showed that changes varied with ultrasound frequency and time course after exposure to high intensity focused ultrasound. We suggest that high intensity focused ultrasound might prove useful in occluding arteries when treating tumors in the clinical setting.