A method of digitally constructing and visually displaying brain function activity using a system for scanning, mapping and visually displaying functional brain activity, the system comprising a scanner and a host computer, wherein the scanner includes its own microprocessors and code which control a radial movement and relative timing between the detectors, performs data acquisition via multiple arrays of photomultiplier tubes and transmits the data via serial cable to the host computer, the scanner comprising a gantry supporting a plurality of gamma ray detectors, each of said plurality of detectors having a converging collimator for collecting gamma rays emitted from a radioactive source in the brain, at least a scintillation crystal is attached to an end of each collimator for converting the emitted gamma rays from the brain into photons of light and at least a photomultiplier tube is coupled to each scintillation crystal for producing a count of emitted gamma rays; a data processor for digitally compiling the count of gamma radiation and visually reconstructing a digital image reflecting the emitted gamma radiation on a display device, each of the plurality of converging collimators is a short focus collimator having a focal point within the scanned radioactive source, the method comprising the steps of: scanning gamma radiation emitted by the brain along a first slice with the plurality of gamma ray detectors, and storing scan data; repeating the scanning of the gamma radiation emitted along a sequentially adjacent slice of the brain and subsequent slices up to a number of slices which has been sent to the scanner by the host computer and storing scan data as actual scan data, wherein a bed is moved in an axial direction to enable the collimators to scan the next slice, wherein a 2-dimensional, slice-by-slice reconstruction is performed while the scan is taking place for the purpose of visually monitoring the progress of the scan; upon completion of acquiring a complete data set for each slice and reconstructing this data into a complete visually observable 2-dimensional slice, performing a full 3-dimensional reconstruction, wherein both the 2-dimensional and the 3-dimensional reconstructions incorporate a maximum a-posteriori algorithm involving an iterative process which comprises the steps: of estimating a distribution of radioactivity in the brain with the estimated distribution being zero for an initial estimation step, preforming a simulated scan of the estimated distribution to obtain the simulated scan, comparing the simulated scan data with the actual scan data, modifying the estimated distribution of radioactivity to obtain a second simulated scan data so that on the next iteration the simulated scan data will better match the real data, determining whether the actual scan data and the simulated scan data agree within the known statistical noise of the actual scan data; and reiterate the comparing and modifying until the simulated scan data and the actual scan data agree within the known statistical noise of the actual data, visually displaying an image of the brain function activity based on the reconstructed image of the brain function. scanning gamma radiation emitted by the brain along a first slice with the plurality of gamma ray detectors, and storing scan data; repeating the scanning of the gamma radiation emitted along a sequentially adjacent slice of the brain and subsequent slices up to a number of slices which has been sent to the scanner by the host computer and storing scan data as actual scan data, wherein a bed is moved in an axial direction to enable the collimators to scan the next slice, wherein a 2-dimensional, slice-by-slice reconstruction is performed while the scan is taking place for the purpose of visually monitoring the progress of the scan; upon completion of acquiring a complete data set for each slice and reconstructing this data into a complete visually observable 2-dimensional slice, performing a full 3-dimensional reconstruction, wherein both the 2-dimensional and the 3-dimensional reconstructions incorporate a maximum a-posteriori algorithm involving an iterative process which comprises the steps: of estimating a distribution of radioactivity in the brain with the estimated distribution being zero for an initial estimation step, preforming a simulated scan of the estimated distribution to obtain the simulated scan, comparing the simulated scan data with the actual scan data, modifying the estimated distribution of radioactivity to obtain a second simulated scan data so that on the next iteration the simulated scan data will better match the real data, determining whether the actual scan data and the simulated scan data agree within the known statistical noise of the actual scan data; and reiterate the comparing and modifying until the simulated scan data and the actual scan data agree within the known statistical noise of the actual data, visually displaying an image of the brain function activity based on the reconstructed image of the brain function.