82 SUBMILLIMETER NUCLEAR MEDICAL IMAGING WITH A COMPTON CAMERA USING TRIPLE COINCIDENCES OF COLLINEAR BETA+− ANNIHILATION PHOTONS AND GAMMA RAYS

摘要

Modern PET systems reach a spatial resolution of 3-10 mm. A disadvantage ofthis technique is the diffusion of the positron before its decay with a typicalrange of ca. 1 mm (depending on its energy). This motion and Compton scatteringof the 511 keV photons within the patient limit the performance of PET. Wepresent a nuclear medical imaging technique, able to reach submillimeterspatial resolution in 3 dimensions with a reduced activity application comparedto conventional PET. This 'gamma-PET' technique draws on specific positronsources simultaneously emitting an additional photon with the eta+ decay.Exploiting the triple coincidence between the positron annihilation and thethird photon, it is possible to separate the reconstructed 'true' events frombackground. In order to test the feasibility of this technique, Monte-Carlosimulations and image reconstruction has been performed. The spatial resolutionamounts to 0.2 mm (FWHM) in each direction, surpassing the performance ofconventional PET by about an order of magnitude. The simulated detectorgeometry exhibits a coincidence detection efficiency of 1.92e-7 per decay.Starting with only 0.7 MBq of source activity (ca. 200-500 times less comparedto conventional PET) an exposure time of 450 s is sufficient for sourcereconstruction.