FIG. 4

The limited resolution of PET and SPECT scanners blurs activity from two discrete point sources (A and B), resulting in the apparent spatial diffusion of activity into regions with no radioactivity. Viewed in one dimension, the activity distribution from each source appears as a Gaussian curve referred to as the point spread function. Camera resolution is defined as the full width of the point spread function at half of its maximum activity (FWHM). When separated by a distance equal to the FWHM, two point sources of identical activity begin to demonstrate a modest decrease at the midpoint of their summed activities, suggesting that the original source consisted of two points rather than one.

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published 2000