The architectural impact of single photon transmission measurements on full ring 3-D positron tomography

For the full potential of high resolution (2 to 4 mm) full ring 3-D positron emission tomography (PET) to be realized, reductions in both scan time and noise for measured attenuation correction must be provided. Recent advancements in 3-D PET transmission measurements have been demonstrated using a point source and collecting single photon gamma radiation. Greater than an order of magnitude increase in counting statistics for 3-D acquisitions is possible over traditional dual photon techniques such as rotating rods. Usable single photon transmission scans as short as 2 minutes are practical. Such short scans will have reduced noise due to counting rates in excess of 2.5 M events/sec. Acquiring single photon transmission data in full ring 3-D PET requires several architectural additions to the tomograph. Additions include: 1) a "place holding" mode for the coincidence processor, 2) real-time single photon line of response rebinning electronics, 3) a liquid drive for moving a 4 mCi /sup 137/Cs point source at 1 metre/sec around the field of view, and 4) a fiber-optic detector system for tracking the point source position and speed. Initial implementation of these changes supports a first-of-its-kind 82 cm diameter, 23 cm axial length high resolution full ring 3-D PET tomograph.