Reduced parallel anode readout for 256 ch flat panel PMT

SPECT and PET need a good pixel identification to obtain high quality images. This is why new generations of PSPMT with anode array with smaller step have been developed till the recent flat panel PMT H9500 with 2" square area, 256 anodes array, 3 mm individual pitch. The realization of electronic chains with so high number channels demands dedicated electronics readout with high cost and high management difficulty. In this work we propose a new method of anode number reduction in parallel readout limiting the total chain number to 64. Starting from the evidence that event charge distribution is always contained inside a portion of the FP PMT anodic plane, we assume that only a quarter of the anodes are involved in the detection. Our approach consists on virtually dividing 16times16 anodes in 4 arrays with 64 anodes per each. Once the charge distribution is collected by the 4 anodic planes, each individual anodic charge is projected on one plane. Physically, each i,j-element of one quadrant is associated to the corresponding i,j-element of the other three matrices. In terms of hardware, it is simply realized connecting one to each other the set of four i,j-anodes of the 4 quadrants. In this work an image reconstruction software has been developed and tested by measured charge distribution collected by 256 anodes Hamamatsu FP PMT. The final results, in term of spatial resolution and position linearity, are in agreement with ones collected by the total number of anodes