Abstract

Effects of Pulsed Focused Ultrasound at Pressures Beyond the Cavitation Threshold: Histological Study on Rabbit Brain in Vivo

N.Vykhodtseva, N.Mcdannold, K.Hynynen (Focused Ultrasound Laboratory, Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA)

e-mail: Natalia@bwh.harvard.edu

Objective: To study histological effects of high intensity short-pulsed focused ultrasound on mammalian tissues. Methods: The brains of 16 New Zealand white rabbits were sonicated in 4-6 locations after craniotomy (intact skin&dura) using a 1.63 MHz focused transducer (D/F =10 cm / 8 cm). Sonications were performed for 10 s, with burst lengths ranging between 1 to 100 ms and an RPF of 1 - 100 Hz. MR-imaging was used to aim the beam, monitor the exposure, and evaluate the effects. Histological examination was performed 2-48 hours after sonications. Results: We found that high intensity short-pulsed sonications could effectively destroy targeted tissue without evidence of thermal or cavitation effects. The destroyed tissue was observed to be almost completely homogeneous. The lesioned regions contained scattered erythrocytes arranged in a helically coiled, layered fashion. In the more severe lesions, the core appeared almost completely liquefied with erythrocytes swept out from the center area to its periphery. Conclusion: High intensity focused ultrasound can cause tissue damage by destroying brain tissue due only to the mechanical impact of ultrasound beam. These results are very preliminary, but may shed light into important aspects of the interaction of the ultrasound beam as it propagates through organized tissue.

Section : 5