Uniformity correction for SPECT using a mapped cobalt-57 sheet source.

As little as 1% nonuniformity of the scintillation camera can produce disturbing artifacts in SPECT images. To correct for nonuniformity, acquired images must be divided by the flood-field image of a uniform sheet source. The refillable 99mTc sheet source requires meticulous preparation before each use, and is subject to spillage. We propose the use of a permanent 57Co solid sheet source in conjunction with a map of the radioactivity distribution in the source. The flood-field image of the cobalt source is converted by the map into the equivalent of a flood-field image of an almost perfectly uniform source. An accurate and reproducible method is described for generating a map of the cobalt sheet source from images of it made in multiple positions with the scintillation camera. The mapping process is independent of sensitivity variations across the face of the camera.