Principles of Medical Imaging for Engineers by Michael Chappell

Author:Michael Chappell
Language: eng
Format: epub
ISBN: 9783030305116
Publisher: Springer International Publishing

8.6 PET

The added information we get with PET is that each emission gives rise to two gamma photons launched at precisely 180° to each other. Thus, by pairing up detections, we can more precisely locate the line on which the emission occurred—the line of response (LoR). To do this, we need a ring of detectors mounted around the subject to simultaneously record all emissions that arise within the body.

PET reconstruction relies upon coincidence detection : to determine the line of response , we need to identify the two detectors at which two separate photons from the decay process have arrived. PET systems typically operate with time windows of the order of 12 ns. Any two photons received within that window are presumed to have come from the same emission event—are coincident—and thus an emission must have occurred along the LoR that connects those two detectors. This is illustrated in Fig. 8.6, where an event is recorded as having occurred on the LoR between sensors 3 and 12 based on an overlap in the signals generated in both detectors in response to a received photon (which has been converted to a signal of duration τ seconds).

Fig. 8.6The principle of coincidence detection . An event is recorded as having occurred on the LoR connecting detectors 3 and 12 based on signals being generated by both within the specified time window

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