Ultrasound in Neurology

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Abstract
By appropriate selection of dosage and conditions of irradiation, ultrasound can selectively destroy the neural components of the central nervous system without interrupting the blood vessels traversing the affected region. The neural components of white matter can be completely destroyed without disrupting neighboring or surrounding gray matter. By using focussed beams any desired depth in the brain can be reached without damaging intervening tissue. Lesions as small as a few cubic millimeters can be realized and larger lesions of almost any desired shape can be produced in white matter by moving the focus of the sound beams in the tissue. Under appropriate conditions a higher dosage of ultrasound is required for affecting gray matter than is required for producing irreversible changes in white matter. Under certain ultrasonic dosage conditions nerve fibers in both white and gray matter can be demyelinated, as observed histo-logically, without destruction of the axis cylinders. The only surgery which is essential to the ultrasonic procedure is the removal of the appropriate amount of bone to admit the sound beams. Bone is highly absorbing for ultrasound and would also distort the beams as they traversed it. Sterile degassed saline serves as a transmitting liquid to conduct the sound to the brain. This liquid is supported by a "pan" which is fastened to the skin of the subject. The duration of the irradiation period is of the order of 1 to 3 seconds at each position. The various types of lesions which can be produced are illustrated by photographs of stained tissue sections. The instrument described in the paper is a prototype for human neurosurgery. It is designed to be incorporated into a double room arrangement with the supporting and positioning system housed above the operating room. A tube supported by the positioning system and projecting through the ceiling of the irradiation room supports the focussing irradiator. The operating room contains all of the controls necessary for the irradiation procedure.