A lower-cost high-resolution LYSO detector development for positron emission mammography (PEM)

Wt have developed several positron emission tomography (PET) cameras using photomultiplier-quadrant-sharing (PQS) geometry; in which each detector block is optically coupled to four round PMTs, and each PMT is shared by four blocks. Although PQS design reduces the cost of high-resolution PET systems, when the camera consists of detector panels that are made up of square blocks, half of the PMT's sensitive window remains unused at the detector panel edge. Our goal was to develop a LYSO detector panel, which minimize the unused portion of the PMTs while maintaining the low cost, high resolution, and high sensitivity of positron emission mammography (PEM) camera. Our plan was to modify PQS design by using elongated blocks at panel edges and square blocks in the inner area. For elongated blocks, symmetric and asymmetrical reflector patterns were developed, and PQS and PMT-half-sharing (PHS) arrangements were implemented in order to obtain a suitable decoding. The performance of our blocks was good, producing good crystal-decoding and average energy resolution. Using a modified PQS geometry and asymmetric block design, we reclaimed the unused PMT region at detector panel edges, thereby increasing field-of-view and overall detection sensitivity and minimizing undetected breast region near the chest wall. This lower cost design using regular round PMT allowed us to use larger detector panels and hence to build a lower-cost, high-resolution, high-sensitivity PEM camera.