Ultrasonically Produced Changes in the Blood-Brain Barrier

It has been demonstrated in recent years * that focused ultrasound of frequencies ranging from 0.9 to 2.5 megacycles (mc), and at intensities of from 200 to 1500 watts per square centimeter, may be used to produce circumscribed small lesions in the central nervous system. Histological examination of the tissue damaged by focused ultrasound does not reveal the mechanism of destruction, although the morphological appearance of ultrasonic lesions differs specifically from other types of lesions.2 A cardinal point in understanding the effect of ultrasound on central nervous tissue is knowledge of the reaction of the cerebral capillaries to this type of injury. Both the absence of gross hemorrhage and the existence of edema have been reported by some investigators.† Thus, the extent of capillary damage and its possible role in the development of a lesion are important from the point of view of the physiological effect of ultrasound. For this