Singles attenuation correction in positron tomography

The authors have modified an ECAT 953 to count all incident photons (or singles) opposite a rotating point source. The source location is monitored by a `singles converter´ and used to rebin the source lines of response into coincidence sinograms. Count rate studies indicate that up to 60,000 counts per second per detector ring are recorded with a 3 mCi point source. Above this source strength, the detector blocks begin to saturate resulting in decreased contrast. Useful data for chest imaging is obtained in 15 seconds per plane, with no sinogram smoothing necessary. Scatter is increased slightly in singles mode. This is reflected in the low value of the measured attenuation coefficient for water of 0.069 [cm^-1]. With the interplane septa removed, the authors anticipate that all of the attenuation factors needed for three dimensional reconstruction can be measured in as little as 4 minutes