Measurements on the timing stability of the MicroPET R4 animal PET scanner

• Published in: IEEE Symposium Conference Record Nuclear Science 2004 Vol. 5; pp. 2885 - 2889
• Main Authors: Thompson, C.J., Goertzen, A.L.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 2004
• Subjects: Animals; Attenuation; Crystals; Energy resolution; Optical arrays; Position sensitive particle detectors; Positron emission tomography; Sensor arrays; Stability; Timing
• ISBN: 9780780387003; 0780387007
• ISSN: 1082-3654; 2577-0829
• DOI: 10.1109/NSSMIC.2004.1466289

The MicroPET R4 and P4 small animal PET scanners have detectors consisting of an array of 64 2.1times2.1times10 LSO crystals coupled via light guides to Hamamatsu R5900-C12 position sensitive PMTs. These have energy resolutions in the range of 25% and timing resolutions <3 nsec. The calibration software allows users to set up the crystal identification maps and voltage to keV conversion gain for each crystal in a mostly automated and highly interactive way. However until recently there was no provision for making adjustments to the inter-detector timing alignment. Our preliminary evaluation of this instrument showed that reasonable normalization sinograms could only be obtained with a timing window of 10 nsec or more in spite of a timing resolution of <3 nsec. We performed sham transmission scans with nothing in the field of view, and a range of timing windows from 2 to 14 nsec and used a 14 nsec timing blank scan to generate effective attenuation sinograms as a function of timing window. These showed trues count-rates which fit well to a ERF(tau) function. However, the effective attenuation value, which should be 1.0, changes from block to block becomes very high (<3.5 at 6 nsec.) in some blocks suggesting the need for timing alignment. In the latest software release, V5.2.2.8, timing alignment is permitted, and the timing is much better aligned and much more stable