Allegro的电子学设计

Imaging Characteristics of a 3-Dimensional GSO Whole-Body PET Camera
Suleman Surti, PhD; and Joel S. Karp, PhD
THE JOURNAL OF NUCLEAR MEDICINE • Vol. 45 • No. 6 • June 2004

The electronics architecture for the Allegro is derived from the original PENN PET design (4) with appropriate upgrades to use new advancements in technology. The output from each PMT enters an analog preamplifier channel for pulse amplification, followed by signal digitization with 50-MHz, flash (asynchronous) analog-to-digital converters. Concurrently, the analog preamplifier outputs of the PMTs are also summed into 28 overlapping trigger channels, each consisting of a group of 20 PMTs. Each trigger signal passes through a constant fraction discriminator (CFD) to obtain trigger timing information for high-energy deposition events in the detector. The overlapping triggering scheme and good system energy resolution provide the capability to raise the trigger CFD threshold as high as 400 keV, thereby reducing the scanner dead time significantly. The trigger signals are formed before PMT gain matching and, since the gains can vary by as much as a factor of 4, the CFD threshold is set lower than the final software energy lower level discriminator (ELLD) that sets a gate for events that are histogrammed in the sinogram. With a CFD threshold of around 400 keV, we are able to achieve uniform event distribution over the entire scanner area. The CFD signals are then checked for coincident events and, once a coincidence is detected (within a timing window, 2t