detector. However, as can be seen from Figure 13.11, the use of a larger
diameter of the ring improves this effect. Correction can be made for
this effect by measuring light in the front and back of each detector and
using the difference to measure the depth of the photon interaction in the
detector.
Performance of PET Scanners
Spatial Resolution
The spatial resolution of a PET scanner is defined by several factors that
are discussed below.
Performance of PET Scanners 201XdFig. 13.11. An illustration of radial elongation. An off-center event (solid line)
strikes the back of the detector pair tangentially. The X-,Y-positioning of the detec-
tors (dashed line) is a distance daway from the actual location of the positron anni-
hilation, causing the blurring of the image. (Reprinted with the permission of the
Cleveland Clinic Foundation.)