ABSTRACT
Magnetic resonance imaging (MRI)-guided noninvasive ultrasound treatment of the brain
has substantial advantage over invasive neurosurgery in which unavoidable disruption of
anatomic structures results in functional disturbances. Since the early 1940s, the potential
of focused ultrasound to produce focal, targeted deep destruction within the brain has
been researched extensively. Early on, animal and clinical results were encouraging,
showing well-defined tissue coagulation at the focal zone (1-5). However, the experi-
ments of Lynn et al. (6) demonstrated that ultrasound is strongly attenuated by bone, and
the energy loss increases bone temperature, resulting in brain-tissue coagulation close to
the skull. Another problem is related to the variable thickness and density of the skull
bone, which results in distortion of the ultrasound wave front propagating through the
bone. Because of these two problems, it is difficult to focus ultrasound beams through
the cranium. As a result, most scientists accepted that therapeutic ultrasound could not be
delivered through an intact skull.
