Manabu Hamamoto

Performance evaluation of a subset of a four-layer LSO detector for a small animal DOI PET scanner: jPET-RD

Previously, we proposed a new depth of interaction (DOI) encoding method and proved that it worked successfully with four-layered Gd/sub 2/SiO/sub 5/ crystals for a small animal positron emission tomography (PET) detector. We are now planning to develop a small animal PET scanner, jPET-RD (for rodents with DOI detectors), which has both high resolution and high sensitivity by the use of a DOI detector with a 32/spl times/32/spl times/4 crystal array. The scintillator for the detector will be Lu/sub 2(1-x)/Y/sub 2x/SiO/sub 5/ (LYSO). In this work, we evaluated performance of a DOI detector composed of four layers of a 12/spl times/12 LYSO (Lu: 98%, Y: 2%) crystal array by irradiating 511 keV gamma rays uniformly. The new encoding method was used for crystal identification. The size of each crystal was 1.46 mm/spl times/1.46 mm/spl times/4.5 mm. The crystal block was coupled to a 256-channel flat panel position sensitive photomultiplier tube, which has 16/spl times/16 multi anodes at intervals of 3.04 mm. As we expected, all crystals are expressed on a single two-dimensional position histogram without overlapping. Energy resolution of all events is 21.8% and time resolution of all events is 0.69 ns in FWHM. When layers are counted from the top, the energy resolutions of the first, second, third, and fourth layer events are 11.6%, 12.3%, 13.3%, and 19.1% and the time resolutions are 0.60ns, 0.59ns, 0.60ns, and 0.66ns, respectively.

Preliminary evaluation of four-layer BGO DOI-detector for PET

We found that Bi/sub 4/Ge/sub 3/ O/sub 12/ (BGO) scintillator can be elements of a four-layer depth of interaction (DOI) detector and it was proved with a 12/spl times/12/spl times/4 array of BGO crystals in dimensions of 2.9 mm/spl times/2.9 mm/spl times/7.5 mm coupled to a 256-channel flat panel position sensitive photomultiplier tube. Appropriate reflector insertion in the array makes all crystal identification possible on one position histogram. Despite the large refractivity and small light output of BGO, the four-layer BGO detector showed no significant variation in the full energy peaks among all crystal elements. When no optical grease was used in the construction of the BGO DOI-block and irradiated with gamma-rays from /sup 137/Cs, a top layer crystal has 80% of light output relative to the bottom layer. The obtained two-dimensional position histogram by the irradiation was clear enough to allow identification of the crystals of interaction. Profiles of the histogram show peak-to-valley ratio of 1.9:1 for the top layer crystals and larger ratio for other layer crystals in the experiment.

Performance evaluation of a four-layer LSO detector for a small animal DOI PET scanner: jPET-RD

Previously we proposed a new depth of interaction (DOI) encoding method and proved that it worked successfully with four-layered Gd/sub 2/SiO/sub 5/ crystals for a small animal positron emission tomography (PET) detector. We are now planning a small animal PET scanner, jPET-RD (for Rodents with DOI detectors), which has both high resolution and high sensitivity. Scintillator for the scanner will be Lu/sub 2(1-x)/Y/sub 2x/SiO/sub 5/ (LYSO). In this work, we evaluated the DOI detector composed of four layers of 12/spl times/12 LYSO (Lu: 98%, Y: 2%) crystal array by irradiating 511 keV uniform gamma rays. For crystal identification, the new encoding method was used. The size of each crystal is 1.44 mm/spl times/1.44 mm/spl times/4.5 mm. The crystal block was coupled to a 256-channel flat panel position sensitive photomultiplier tube, which has 16/spl times/16 multi anodes at intervals of 3.04 mm. In this measurement, all crystals are expressed on a single two-dimensional position histogram without overlapping as we expected. Energy resolution of all events is 21.8 % and time resolution of all events is 0.69 ns in FWHM. The energy resolutions of the first, second, third, and fourth are 11.6%, 12.3%, 13.3%, and 12.5% and the time resolutions are 0.60 ns, 0.59 ns, 0.60 ns, and 0.66 ns, respectively.

Measurement of 32/spl times/8/spl times/4 LYSO crystal responses of DOI detector for jPET-RD

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

BGO DOI-detector composed of three-dimensional crystal array for PET

We found that Bi4Ge3O12 (BGO) scintillator can be a feasible alternative for a 4-layer depth of interaction (DOI) detector and was proved with a 12times12times4 array of BGO crystals in dimensions of 2.9 mmtimes2.9 mmtimes7.5 mm coupled to a 256 channel flat panel position sensitive photomultiplier tube. Appropriate reflector insertion in the array makes all crystal identification possible on one position histogram. Despite the large refractivity and small light output of BGO, the 4-layer BGO detector showed no significant variation in the full energy peaks and energy resolutions among crystal elements. When no optical grease was used in the construction of the BGO DOI-block and irradiated with gamma-rays from 137Cs, 0.71 full energy peak of a top layer crystal relative to a bottom layer crystal and about 20 % energy resolutions for each layer crystal was achieved. The obtained two-dimensional position histogram from the irradiation was clear enough to allow identification of the crystals of interaction. Profiles of the histogram show peak-to-valley ratio of 1.9:1 for the top layer crystals and larger ratio for other layer crystals