Suitability of a 280 ps-CRT non-DOI detector for the helmet-neck PET

Sodai Takyu,Eiji Yoshida,Taiga Yamaya,Abdella M Ahmed,Taichi Yamashita,Hideaki Tashima

doi:10.1109/nssmic.2017.8532709

Sodai Takyu, Eiji Yoshida + Show 4 more

https://doi.org/10.1109/nssmic.2017.8532709

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We are developing a compact and high-sensitivity brain-dedicated PET scanner, which consists of a hemispherically arranged detector unit and an add-on detector unit. Following our first idea of using a chin position as the location of the add-on detector (helmet-chin PET), a neck position has been selected as the location (helmet-neck PET). We have developed prototypes of both geometries using the 4-layered depth-ofinteraction (DOI) detector (2.8 mm sized GSOZ scintillators and a 64 ch PMT) which does not have time-of-flight (TOF) capability. On the other hand, a new TOF-PET detector module which consists of 4.1 mm sized LFS scintillators and multi pixel photon counters (MPPCs) is now commercially available (C135004075LC-12, Hamamatsu Photonics K.K.). Using one-to-one crystal-photodetector coupling, it is possible to achieve a 280 ps coincidence resolving time (CRT), although the Anger-type calculation, which is essential for the 4-layered DOI detector, cannot be applied. In this paper, therefore, we investigated the suitability of this TOF-PET detector module for the next helmetneck PET. At first, the helmet-neck PET with 20 mm crystal length, which is a standard parameter of the module, was modeled by GEANT4, and performance results were compared with those of the current helmet-neck PET prototype. We observed a compromised image quality; the non-DOI capability counteracted the TOF gain. On the other hand, the helmet-neck PET with shortened crystal length (10 mm) outperformed the current helmet-neck PET prototype; the shortened crystal length reduced the parallax error, and TOF information compensated for the loss of sensitivity. Based on the GEANT4 simulation results, we fabricated a one-pair prototype of the TOF-PET module with 10 mm length, which yielded 11.6 % energy resolution at 511 keV and 281.8\pm 9.6 ps CRT at FWHM. In conclusion, we confirmed suitability of the 280 ps-CRT non-DOI detector for the next helmet-neck PET.

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