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.
