A Technique To Reject Scattered Radiation In PET Transmission Scans

It is well known that scattered radiation in PET reduces the contrast in images. There is about the same fraction of scattered events in both emission and transmission scans. The technique presented here reduces the scatter fraction in transmission scans. An orbiting rod source is used in place of the ring source normally used for transmission scans. The source moves in steps rather than in a continuous motion. At each point only coincidences between detector pairs for which the source and detectors are co-linear are accepted. In this way all wide angle scatter is rejected. The attenuation coefficient for water at 511 keV was measured as .095 cm-1 with the orbiting source compared to .086 cm-1 with a conventional source and the value due to the electron density of water .097 cm-1 The recovery coefficient for hollow cylinders 23 mm in diameter increased from 77% for a conventional to 93% for a rod source transmission scan. If the source is collimated to a flat fan beam, a much higher activity could be used, and transmission scans could be performed independent of activity in the patient section being scanned.