PQS Detector Blocks

In the last several years, we have successfully developed several PET systems based on the Photomultiplier-Quadrant-Sharing (PQS) technology using regular round photomultipliers (PMT) and optically coupling them to the detector blocks. The PQS detectors are made up of scintillating crystals with reflective patterns precisely placed between them. Crystals and reflective patterns are glued into a block using optical adhesives. For scintillating crystals we have been using different materials such as bismuth germanate (BGO), gadolinium samarium oxalate (GSO) and cerium-doped lutetium yttrium orthosilicate (LYSO). For reflective patterns we have been using white paint and enhanced spectral reflector (ESR) film. For PMT we have been using round PMTs of different sizes ( 19-mm, 39-mm and 51-mm). The regular round PMTs are less expensive than other types, making them more suitable for development of inexpensive high-resolution PET cameras.

First Generation of PQS-PET Detector Blocks

For the first-generation of the PQS detectors we built square blocks from BGO-crystal slabs glued together and crosscut to certain depth in the direction perpendicular to the slabs. The spread of the scintillation light throughout the block was controlled by the depth of the cuts, filled in with a light-reflecting material and by light barriers painted in specific patterns on the surfaces of the slabs before the slabs were glued together into a block. This methodology increased the detector light output, energy resolution and packing fraction compared to the existing systems at that time (1999). These blocks were used in construction of the variable field prototype PET camera MDAPET. This system was made up of 6,272 BGO-crystal detectors grouped into eight detector-modules with 16 blocks of 7 × 7 crystal array per module (128 blocks) and decoded using 19-mm PMTs.

MDAPET BGO 7 × 7 Detector Block - 19-mm PMTs

Second Generation of PQS-PET Detector Blocks

For the second-generation we used the slab-sandwich-slice (SSS) methodology and improved the performance of the detectors. The blocks were made of BGO-crystals and painted light barriers as in the first generation. See detector blocks comparison. These blocks were used for the construction of the high-resolution oncologic transformable PET (HOTPET) camera and were decoded using the regular 19-mm PMTs. For HOTPET scanner three types of blocks were developed 7 × 7 square, 7 × 8 extended and 8 × 8 double extended blocks.

HOTPET BGO 7 × 8 Detector Block- 19-mm PMTs

HOTPET BGO 8 × 8 Detector Block- 19-mm PMTs

Third Generation of PQS-PET Detector Blocks

For the third-generation, the light sharing specifications were changed. The white paint used as reflective material was replaced by 3M Vikuiti™ ESR (enhanced spectral reflector) film. The ESR film has a much higher reflectivity (98%) which improved the light output of the detector block and therefore improved the decoding capability and the energy spectrum. It also improved the block packing fraction due to the constant and small thickness (0.06 mm) of the ESR film and decreased the production costs, because of the elimination of “crystals painting” step and reducing the production time to one third of previous method. These PQS detector-block was developed for the preclinical rodent research PET (RRPET) camera (commercialized by Gamma Medica -Ideas). For the RRPET camera 8 × 8 BGO pentagon block was developed (using 19-mm PMTs).

RRPET BGO 8 × 8 Detector Block- 19-mm PMTs

New BGO 10 × 10 Detector Block- 19-mm PMTs for preclinical applications

Fourth Generation of PQS-PET Detector Blocks

For the fourth-generation of the PQS detectors the BGO crystals were replaced by LYSO scintillation crystals and the optical auto curing glue for a optical U.V. curing one. Those changes, together with a specific surface finish and the ESR film light blocking reflective patterns, allows increasing substantially the number of crystal detectors per block. This helped to improve the blocks packing fraction, the crystal light output and the crystal-decoding capability over the previous PQS detector blocks. These PQS detector blocks were used in the production of a low cost, high resolution, and high sensitivity of positron emission mammography PEM camera. For the PEM application two types of blocks were developed a 12 × 12 LYSO square and a 12 × 13 LYSO extended blocks and we used the regular round 19-mm PMTs.

PEM LYSO 12 × 12 Detector Block (square) - 19-mm PMTs

PEM LYSO 12 × 13 Detector Block (elongated) - 19-mm PMTs

New Preclinical-PET LYSO 14 × 14 Detector Block- 19-mm PMTs

Fifth Generation of PQS-PET Detector Blocks

For the fifth-generation of the PQS detectors new L(Y)SO blocks have been developed and we have used 39-mm and 51-mm PMTs. These blocks are developed to be used in our futures projects such as time-of-flight PET and a one-meter-long Whole Body PET.