Limitations to head movement of dual-head gamma cameras may prevent pr
oper geometry being attained for testing of intrinsic uniformity with
a point source. When a point source is placed too near to the uncollim
ated crystal, the detected flood image will be non-uniform due to the
inverse square law effect, oblique incidence, and increased path lengt
h traversed through the crystal by oblique rays. A formula has been de
duced for constructing a map to correct for these effects. The general
formula has been applied to a particular dual-head camera in which a
point source has been placed on the face of one head, at 65.5 cm from
the opposite uncollimated crystal. It is shown that division of the no
n-uniform image, acquired with this geometry, by the correction map yi
elds a uniform image which may be used for routine investigation of th
e uniformity characteristics of the camera.