Relationship between objective and subjective assessment of gamma camera image sharpness

In order to relate the performance of the human observer to the objective specifications of a gamma camera system, images of a test object were taken under various conditions that could be expected to cause changes in resolution. Observers were asked to put the images in the order of increasing/decreasing sharpness. For the same physical conditions, objective measurements were made from which the resolution parameters FWHM and FWTM could be derived. By looking for significant differences in ordering of the images, it was possible to show that, within the limitations of the specific system investigated, a fractional change in FWHM of about 10% caused a significant change in image quality. Further experiments to test the universality of this figure are suggested.