Abstract: A test phantom for testing the performance of gamma cameras comprises a plate impervious to gamma rays having an orthogonal array of apertures defined therethrough. The apertures are uniform in size and are arranged in columns and rows. The columns are grouped such that the spacing between adjacent columns in each group differs from the spacing between adjacent columns in all of the groups, and such that the spacing between adjacent columns within each group is uniform throughout that group. The groups are arranged such that the more densely spaced groups are positioned proximate the middle of the array and the more widely spaced columns are disposed at the ends of the array. The resulting test pattern permits changes in the intrinsic resolution, uniformity and spatial distortion of a gamma camera to be observed simultaneously from a single transmission of the test pattern.