SINCE the first automatic radioisotopic scanner was introduced by Cassen et al1 in 1951, with the first scan of a brain tumor by Bender2 in 1956, scanning procedures for the detection of brain lesions have become widely used. These screening procedures provide clinically useful information, are relatively simple to perform, and are of little hazard to the patient. Of fundamental importance, affected tissue is represented rather than secondary anatomical displacements, as in radiologic studies. Scanning has been limited to a screening function because the localization is gross, such as to a lobe or general region of the brain. With the aim of improving the resolution of the γ-ray image from the brain while retaining sensitivity, one of us (B.C.) has designed a radically new detector system consisting of a wideangle converging collimator coupled to a large crystal. This makes possible the resolution of sections of the brain