An automatic brain scanner for use with gamma-ray-emitting isotopes.

Abstract

Two scintillation detectors are simultaneously carried over the surface of a sphere which is concentric with the skull. The collimators for the detectors are arranged so that they accept only those gamma rays which emerge nearly normal to the skull. At present, RISA is being used as the tracer. However, any radioactive element which emits suitable gamma rays and which is preferentially absorbed by the tumor could be used with the scanner. The number of counts received by the two detectors are continually subtracted, so that any asymmetry in the distribution of the tracer is immediately indicated. The difference in count rate from the left and right detector, as well as the total number of counts received from each, are recorded on a circular chart of a size comparable to that of the actual head. By applying this chart directly to the patient's head, the point at which abnormal activity is observed on the chart may be located on the patient. The patient is scanned while supine with his head immobilized in a sling, so designed that it does not interfere with the motion of the detectors. Two points on the record charts are marked to correspond to two points on the head. These points are sufficient for interpretation of the actual position on the patient of any abnormal activity indicated on the chart. While the scan is in progress, the operation of the machine is completely automatic. The procedure, including time for setting up the patient, takes about forty minutes. Suitable scans are obtained with a dose of 250 microcuries of RISA. Scans are taken twenty-four hours after injection of the radioactive tracer. While the device uses the same principle as is employed in manual scans with one detector, it incorporates all the features of an automatic scanning system. The scans are reproducible, since the angles of the detectors with respect to the patient are identical for each scan. The scanner is operating in the Saskatoon Cancer Clinic and a second unit is being constructed for use in the Ontario Cancer Institute. Tests are being carried out on phantom models to establish the limits of the technic from a purely physical point of view. A complete description of the apparatus is being published elsewhere.