| ABSTRACT |
Multiinteraction photon (MIP) coincidences are events coming from a positronelectron annihilation in which more than two γrays are detected simultaneously because at least one of the two original photons deposited its entire energy in more than one detector element. These coincidences are usually discarded in PET scanners as it is not possible to assign them to a unique lineofresponse (LOR). Existing methods to recover MIP events are mainly based on Compton scatter kinematics. We propose a methodology which uses the measured doublecoincidence distribution to sort MIP coincidences into LORs. The PET component of a preclinical PET/CT scanner (Argus/CT, Sedecal S.A., Spain) was adapted to enable the detection and acquisition of MIP coincidences.
The effect of including MIP events recovered using several methods was studied in terms of image quality and noise equivalent count (NEC) rate following the guidelines described in the NEMA NU4 protocol. Recovery of the MIP coincidences using the proposed methodology increased the peak NEC rates by 15.25% and 17.23% when imaging 18 F for mouse and ratsized objects respectively. Furthermore, this method is capable of simultaneously providing better SNR and contrast for hot lesions than those achieved using standard coincidences, while preserving recovery coefficients and contrast in cold lesions. Since the proposed approach can be easily implemented in blockdetector and high granularity detectorbased scanners, this work provides a means to effectively increase the photon sensitivity of new or existing preclinical and clinical PET scanners
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