The BRH Test Pattern consists of an orthogonal array of 2.5 mm diameter holes in a 3.2 mm thick lead plate, 52.4 x 52.4 cm. Other hole diameters can be manufactured as well. The columns of holes have a center-to- center hole spacing of 4 mm, increasing to 9.5 mm. After removal of the collimator, the test pattern is positioned in contact with the detector face. A source of several millicuries (in a syringe or small vial) is placed at least two meters from the center of the test pattern. A few million counts are registered within a short time.99m Tc (140 keV), 133 Xe (81 keV), 201 Tl (69-80 keV) or other radionuclides may serve as sources.
A particular camera’s performance depends on the radiation source and the operating conditions of the instrument. The group of holes with the closest spacing that appears still resolved on the transmission image of the BRH Test Pattern is a measure of the camera’s intrinsic resolution. Non-uniformities superimposed on the hole pattern are recognized more clearly than on a flood image. Spatial distortions appear as displacements of the hole images from the orthogonal grid. All three performance parameters are less clearly displayed by a quadrant-bar image.