Development of a MR compatible brain PET II using 4-side tileable GAPD arrays

There has been great interest in the development of combined PET/MR, a useful tool for both functional and anatomic imaging. We have developed a proof-of-principle MR compatible PET, employing a design concept that uses GAPD arrays as a PET photo-sensor and charge signal transmission method for human brain imaging. The purpose of this study was to design the 2nd version of brain PET with an extended axial field-of-view (FOV) and to evaluate its initial performance. The PET consisted of 18 detector blocks arranged in a ring of 390 mm diameter with 60 mm axial FOV. Each detector block was composed of a 4 × 4 matrix of detector module, each of which consisted of a 4 × 4 array L YSO coupled to a 4-side tileable 4 × 4 GAPD array. The PET gantry was shielded with gold-plated conductive fabric tapes with a thickness of 0.1 mm. PET signals were fed into the position decoder circuit (PDC) generating the digital address and analog pulse of the one interacted channel among the 256 output channels of the detector block, using a 4 m long flat cable. Commercial DAQ modules were used to digitize analog output signals of the PDCs and to store the data in list mode format. The flat cable was shielded with a mesh-type aluminum sheet, which had a thickness of 0.24 mm. All electronics were enclosed in an aluminum box, which had a thickness of 10 mm, located outside the MR bore. Average energy and timing resolutions of the developed PET measured outside the MR room were 18.1±3.2% (n=4,608) and 3.6 ns, respectively. The sensitivity and spatial resolution were 1.2% and 3.1 mm at the center of the field of view, respectively. No significant degradations of PET performance and the uniformity of MR image were observed. Simultaneous PET and MR images of hot-rod phantom and cat brain were successfully acquired. Experimental results indicate that the high performance compact and lightweight PET insert for hybrid PET-MRI can be developed using GAPD arrays and charge signal transmission method.