1. Apparatus for spatial calibration of a gamma camera including a scintillation crystal and an array of photodetectors optically coupled to the scintillation crystal, comprising: a) a mask having a plurality of pinhole apertures arrayed in a non-rectangular distribution; b) a point source of radiation capable of being scanned over the entirety of said plurality of pinhole apertures; and c) a processor for collecting individual point source response data from each of said plurality of pinhole apertures, modeling said point source response data as a Gaussian function, generating at least one Gaussian model patch for the entirety of said mask, transforming said Gaussian model patch using a set of alignment transformation parameters, and using said transformed Gaussian model patch to correct input image data for spatial distortions.