Fig. 5From: Physics of pure and non-pure positron emitters for PET: a review and a discussionTransaxial planes of the reconstructed images of 68Ge/68Ga cylindrical source in the scanner, a without and b with a copper shield. The positrons escaping the phantom annihilate in the copper, which becomes a source of 511 gamma pairs, and are visible in the image as a shell surrounding the phantomBack to article page