jPET-RD is designed to achieve high sensitivity as well as high spatial resolution by the use of four-layer depth of interaction (DOI) information of the detector. We have previously proposed the DOI encoding method that enables four layers DOI identification using only single kind crystal elements. The basic idea was tested by using Gd2SiO5, and the first prototype detector was developed using Lu2(1-x)Y2xSiO5 (LYSO). In this work, we prepared a pair of jPET-RD prototype detectors composed of four layers of a 32 (transaxial)times8 (axial) LYSO (Lu: 98%, Y: 2%) crystal block and a 256-channel flat panel position sensitive photomultiplier tube (256ch FP-PMT). The size of each crystal element is 1.46 mmtimes1.46 mmtimes4.5 mm. The crystal block (46.5 mmtimes11.6 mmtimes18.0 mm) is placed on the central area of a 256ch FP-PMT (49 mmtimes49 mm useful area) and coupled with silicone rubber. First, we evaluated performance of the prototype DOI detector by uniform gamma ray irradiation. Then response functions of the prototype DOI detector were measured with collimated single gamma rays and finally coincidence responses are estimated with a pair of prototype DOI detectors in the experimental setup which simulates jPET-RD system. In the performance evaluation, the energy resolution of all events was 14.7% and the time resolution was found to be 0.66 ns. The response functions were 1.56 mm FWHM and 4.51 mm FWHM in average in transaxial and depth direction, respectively. The FWHMs of coincidence responses were 5.4 mm (non-DOI) and 3.7 mm (averaged DOI). It is confirmed that the spatial resolution is improved by using DOI information
[Show abstract][Hide abstract] ABSTRACT: We have recently proposed a compact, dual-head PET scanner configuration for providing high-sensitivity imaging of small animals. Although the scanner is able to reach a sensitivity of about 30% at the center of imaging field-of-view, its compact configuration produces substantial depth-of-interaction (DOI) blurring and results in significantly degraded spatial resolution. It is known that DOI blurring can be reduced if the system response matrix (SRM), which describes the individual sensitivity of the detection channels of the scanner to image voxels defined in its field of view, can be incorporated in reconstruction. In practice, however, the huge dimension of the SRM found in modern PET scanners make its computation and storage extremely challenging. In this paper, we show that for the dual-head scanner configuration one can employ cubic image voxels having a proper size to create substantial symmetries in the SRM, as a result producing drastic reductions in computation and storage. We have applied this strategy to the proposed high-sensitivity small-animal PET scanner (µPET) to enable accurate computations of its SRM by using Monte-Carlo simulation. Our results with simulated data indicate that the proposed µPET scanner can achieve an isotropic and uniform spatial resolution of ~1.2 mm after incorporating the SRM in reconstruction. In contrast, the image resolution deteriorates significantly and becomes non-isotropic when not employing the SRM: at the center of the scanner, its resolution is ~1.8 mm in directions parallel to the detectors and becomes ~3.2 mm in the direction normal to the detectors. Furthermore, the resolution in the latter direction deteriorates considerably when moving away from the scanner's center. Images generated by with employing the SRM in reconstruction also show substantially better noise properties than those generated without. When applied to a real dataset, considerable enhancement to the image resolution and contrast is obtained when using the SRM in reconstruction.
[Show abstract][Hide abstract] ABSTRACT: Time-of-flight position emission tomography (TOF-PET) is a promising technique for greatly improving image quality. It is well known that depth of interaction (DOI) information can reduce parallax error and uniform the spatial resolution in whole FOV. In this work, we developed three types of DOI detector (non-DOI, 2-layer and 4-layer) for TOF-PET and confirmed whether DOI information can also improve time resolution. The crystal blocks consist of a 16 × 16 Lu1.8Gd0.2SiO5 (LGSO) array. To become the same sensitivity for all crystal blocks, they had the total length in depth direction of the crystal blocks are the same. The size of each crystal element was 3 mm square. The crystal blocks were optically coupled to a 64-channel position sensitive photomultiplier tube, which has 8 × 8 multi anodes at intervals of 6.08 mm. Irradiating 511 keV gamma rays uniformly, All crystal elements of each block are clearly separated on a two-dimensional position histogram. Energy resolutions of non-DOI, 2-layer and 4-layer DOI detectors are 11.1%, 12.0% and 13.0% and time resolutions are 450 ps, 455 ps and 476 ps, respectively.
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