Design and performance of detector modules for the endoscopic PET probe for the FP7-project EndoTOFPET-US

The detection of cancer in its early stage is known to be of key importance to improve cancer treatment and thus reduces mortality and cost. As a consequence, this has led to a growing interest in developing high performance multimodal imaging devices capable of detecting smallest possible tumors. As part of this approach, the EndoTOFPET-US project, a European FP7 program, aims to develop new biomarkers for the pancreatic and prostatic cancers. Testing such markers requires improving the detection of smaller tumors and performing biopsies based on combined anatomic and functional image information. The detection of small tumors using PET detectors also entails high sensitivity and high spatial resolution. One particular objective of this project is to develop a prototype of a novel bi-modal, TOFPET and ultrasound, endoscope for the detection of early stage pancreatic or prostatic tumors. It consists of two separate PET detectors, one a 23×23cm
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total area external plate (placed outside the body) with 256 arrays of 4×4 LYSO crystals of 3.1×3.1×15mm
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size coupled to Hamamatsu MPPC monolithic arrays of 3×3mm
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single sensors, and an internal (endoscopic) PET probe that consists of an array of 9×18 L YSO fibers with a size of 0.71×0.71×10mm
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coupled to a fully digital SiPM [1,2]. This PET tip is attached to a conventional ultrasound endoscope. Electronic 'collimation' provided by time of flight measurements between the external PET plate and the internal PET probe allows the necessary sensitivity to efficiently reject background. This, however, requires a coincidence time resolution of 200ps FWHM. High spatial resolution of ≤ 1mm can be achieved due to the very high granularity of the endoscopic PET probe consisting of crystal pixel sizes of less than 800μm
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section. In this paper we present the design and current development of the PET modules for the endoscopic probe as well as their performance in terms of light yield (LY) and coincidence time resolution (CTR) made with different prototypes.