Cone beam collimation for Single Photon Emission Computed Tomography (SPECT) offers increased sensitivity for brain scanning through more complete use of the detector area. While parallel hole and fan beam geometries for brain imaging can exclude up to 50% of the detector surface converging or cone beam geometries have been investigated using Monte Carlo simulation techniques and are found to yield an increase in sensitivity of between 1.4 and 3 times. A fully three dimensional Inverse Monte Carlo (IMOC) reconstruction algorithm has been developed for cone beam acquisition which includes compensation for attenuation. Copyright © 1986 by The Institute of Electrical and Electronics Engineers, Inc.