• Journal of Radiation Industry
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• v.9 no.3
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• pp.143-151
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• 2015

A PET-MR system is particularly useful in diagnosing brain diseases. We have developed a prototype positron emission tomography (PET) system which can be inserted into the bore of a whole-body magnetic resonance imaging (MRI) system that enables us to obtain PET and MRI images simultaneously with a reduced cost. Silicon photomultipliers (SiPM) are appropriated as a PET detector at PET/MR system because detectors have a high gain and are insensitive to magnetic fields. Despite of its improved performance compared to that of PMT-based detectors, there is a problem of the photo-peak channel shift which is due to the increase of the temperature inside the ring detector. This problem will occur decreasing sensitivity of the PET and image distortion. In this paper, I quantitative analyze parameters of the KAIST SiPM depending on temperature by experiments. And I designed cooling methods in consideration of the degradation of sensors for correction of the temperature in the PET gantry. According to this research, we expect that distortive images and degradation of the sensitivity will not be occurred with using the above idea to reduce heat even if the PET system operates for a long time.

• Nuclear Engineering and Technology
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• v.52 no.10
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• pp.2346-2352
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• 2020

Dual-energy x-ray absorptiometry (DXA) is the noninvasive method to diagnose osteoporosis disease characterized by low bone mass and deterioration of bone tissue. Many global companies and research groups have developed the various DXA detectors using a direct photon-counting detector such as a cadmium zinc telluride (CZT) sensor. However, this approach using CZT sensor has some drawback such as the limitation of scalability by high cost and the loss of efficiency due to the requirement of a thin detector. In this study, a SiPM based DXA system was developed and its performance evaluated experimentally. The DXA detector was composed of a SiPM sensor coupled with a single LYSO scintillation crystal (3 × 3 × 2 ㎣). The prototype DXA detector was mounted on the dedicated front-end circuit consisting of a voltage-sensitive preamplifier, pulse shaping amplifier and constant fraction discriminator (CFD) circuit. The SiPM based DXA detector showed the 34% (at 59 keV) energy resolution with good BMD accuracy. The proposed SiPM based DXA detector showed the performance comparable to the conventional DXA detector based on CZT.

• IEIE Transactions on Smart Processing and Computing
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• v.4 no.5
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• pp.324-329
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• 2015

A decreased number of readout method is investigated to provide precise pixel information for small-animal positron emission tomography (PET). Small-animal PET consists of eight modules, and each module is composed of a $6{\times}6$ array of $2{\times}2{\times}20mm^3$ lutetium yttrium orthosilicate (LYSO) crystals optically coupled to a $4{\times}4$ array of $3{\times}3mm^2$ silicon photomultipliers (SiPMs). The number of readout channels is reduced by one-quarter that of the conventional method by applying a simplified row and column matrix algorithm. The performance of the PET system and detector module was evaluated with Geant4 Application for Emission Tomography (GATE) 6.1 and DETECT2000 simulations. In the results, all pixels of the $6{\times}6$ LYSO array were decoded well, and the spatial resolution and sensitivity, respectively, of the PET system were 1.75 mm and 4.6% (@ center of field of view, energy window: 350-650 keV).

• Journal of the Korean Society of Radiology
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• v.13 no.3
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• pp.319-324
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• 2019

A depth-encoding detector module with silicon photomultipliers(SiPMs) using two layers of scintillation crystal array was designed, and the position measurement capability was verified using DETECT2000. The depth of interaction of the crystal pixels with the gamma rays was tracked through the image acquired with the combination of surface treatment of the crystal pixels and reflectors. The bottom layer was treated as a reflector except for the optically coupled surfaces, and the crystals of top layer were optically coupled each other except for the outer surfaces so that the light sharing was made easier than the bottom layer. Flood images were obtained through the combination of specular reflectors and random reflectors, grounded and polished surfaces of crystal pixels, and the positions at which layer images were generated were measured and analyzed. The images were reconstructed using the Anger algorithm, whose the SiPM signals were reduced as the 16-channels to 4-channels. In the combination of the grounded surface and all reflectors, the depth positions were discriminated into two layers, whereas it was impossible to separate the two layers in the all polished surface combinations. Therefore, using the combination of grounded surface crystal pixels and reflectors could improve the spatial resolution at the outside of the field of view by measuring the depth position in preclinical positron emission tomography.

• Nuclear Engineering and Technology
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• v.47 no.4
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• pp.479-487
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• 2015

The thallium-doped sodium iodide [NaI(Tl)] scintillation detector is preferred as a gamma spectrometer in many fields because of its general advantages. A silicon photomultiplier (SiPM) has recently been developed and its application area has been expanded as an alternative to photomultiplier tubes (PMTs). It has merits such as a low operating voltage, compact size, cheap production cost, and magnetic resonance compatibility. In this study, an array of SiPMs is used to develop an NaI(Tl) gamma spectrometer. To maintain detection efficiency, a commercial NaI(Tl) $2^{\prime}{\times}2^{\prime}$ scintillator is used, and a light guide is used for the transport and collection of generated photons from the scintillator to the SiPMs without loss. The test light guides were fabricated with polymethyl methacrylate and reflective materials. The gamma spectrometer systems were set up and included light guides. Through a series of measurements, the characteristics of the light guides and the proposed gamma spectrometer were evaluated. Simulation of the light collection was accomplished using the DETECT 97 code (A. Levin, E. Hoskinson, and C. Moison, University of Michigan, USA) to analyze the measurement results. The system, which included SiPMs and the light guide, achieved 14.11% full width at half maximum energy resolution at 662 keV.