Attenuation correction in positron emission tomography (PET) is usually achieved using a transmission scan, which is typically performed with one or several rotating rod sources containing a positron emitter such as Ge- 68. Since good statistics is required in the transmission scan, the imaging time is typically 10 to 20 minutes and the activity in the rod sources is as high as the scanner countrate capability permits. We propose to perform the transmission scan with a singles gamma-ray emitter, namely Cs-137, which has an energy of 662 keV, i.e. somewhat higher so that energy discrimination can be used to separate its energy from that of a positron emitter. Since only the transmitted gamma-rays are used and the source is shielded towards the nearer detectors, higher countrates and therefore shorter transmission scan can be obtained. During the Phase I we have demonstrated that high quality transmission scans can be achieved in as little as 2 minutes.
The completed singles transmission apparatus using a Cs-137 source will become a valuable enhancement for the PENN-PET scanners manufactured by UGM Medical Systems, improving the ease of performing attenuation correction and reducing the total patient examination time. The technique is potentially applicable to all PET scanners.
