Nuclear Medicine and Molecular Imaging

The Korean Society of Nuclear Medicine (대한핵의학회)
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Development of Position Encoding Circuit for a Multi-Anode Position Sensitive Photomultiplier Tube

다중양극 위치민감형 광전자증배관을 위한 위치검출회로 개발

  • Kwon, Sun-Il (Department of Nuclear Medicine, College of Medicine, Seoul National University) ;
  • Hong, Seong-Jong (Institute of Radiation Medicine, Medical Research Center, Seoul National University) ;
  • Ito, Mikiko (Department of Physics, Korea University) ;
  • Yoon, Hyun-Suk (Department of Nuclear Medicine, College of Medicine, Seoul National University) ;
  • Lee, Geon-Song (Department of Biomedical Engineering, Seoul National University) ;
  • Sim, Kwang-Souk (Department of Physics, Korea University) ;
  • Rhee, June-Tak (Department of Physics, Konkuk University) ;
  • Lee, Dong-Soo (Department of Nuclear Medicine, College of Medicine, Seoul National University) ;
  • Lee, Jae-Sung (Department of Nuclear Medicine, College of Medicine, Seoul National University)
  • 권순일 (서울대학교 의과대학 핵의학교실) ;
  • 홍성종 (서울대학교 방사선의학 연구소) ;
  • 이또우 미끼꼬 (고려대학교 물리학과) ;
  • 윤현석 (서울대학교 의과대학 핵의학교실) ;
  • 이건송 (서울대학교병원 의공학과) ;
  • 심광숙 (고려대학교 물리학과) ;
  • 이준택 (건국대학교 물리학과) ;
  • 이동수 (서울대학교 의과대학 핵의학교실) ;
  • 이재성 (서울대학교 의과대학 핵의학교실)
  • Published : 2008.12.31
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Abstract

Purpose: The goal of this paper is to present the design and performance of a position encoding circuit for $16{\times}16$ array of position sensitive multi-anode photomultiplier tube for small animal PET scanners. This circuit which reduces the number of readout channels from 256 to 4 channels is based on a charge division method utilizing a resistor array. Materials and Methods: The position encoding circuit was simulated with PSpice before fabrication. The position encoding circuit reads out the signals from H9500 flat panel PMTs (Hamamatsu Photonics K.K., Japan) on which $1.5{\times}1.5{\times}7.0\;mm^3$ $L_{0.9}GSO$ ($Lu_{1.8}Gd_{0.2}SiO_{5}:Ce$) crystals were mounted. For coincidence detection, two different PET modules were used. One PET module consisted of a $29{\times}29\;L_{0.9}GSO$ crystal layer, and the other PET module two $28{\times}28$ and $29{\times}29\;L_{0.9}GSO$ crystal layers which have relative offsets by half a crystal pitch in x- and y-directions. The crystal mapping algorithm was also developed to identify crystals. Results: Each crystal was clearly visible in flood images. The crystal identification capability was enhanced further by changing the values of resistors near the edge of the resistor array. Energy resolutions of individual crystal were about 11.6%(SD 1.6). The flood images were segmented well with the proposed crystal mapping algorithm. Conclusion: The position encoding circuit resulted in a clear separation of crystals and sufficient energy resolutions with H9500 flat-panel PMT and $L_{0.9}GSO$ crystals. This circuit is good enough for use in small animal PET scanners.

목적: 소동물용 PET은 우수한 공간분해 능과, 민감도가 요구된다. 본 연구에서는 256개의 개별적 채널을 4개로 줄여 검출위치를 추정할 수 있는 회로를 설계하고 제작하였으며, 256($16{\times}16$)개의 양극 출력 채널을 가지는 고집적도의 광전자증배관 및 $L_{0.9}GSO$ 섬광결정과 결합하여 그 성능을 검증하였다. 대상 및 방법: 설계한 회로를 제작하기에 맞서 전자회로 시뮬레이션을 통해 성능을 예상하였다. 회로의 검증과 성능분석을 위하여 위치결정회로, H9500(Hamamatsu Photorucs K.K., 일본) 광전자증배관, $1.5{\times}1.5{\times}7.0\;mm^3$ $L_{0.9}GSO$ 섬광결정으로 두 개의 검출단을 제작하고 $3.7{\times}10^5$ Bq의 $^{22}Na$ 방사선원을 사용하여 동시이벤트를 검출하였다. 첫 번째 검출단은 $L_{0.9}GSO\;29{\times}29$ 섬광결정블록을 단층으로 구성하였고, 두 번째 검출단은 $L_{0.9}GSO\;29{\times}29$와 $28{\times}28$ 섬광결정블록을 x와 y방향으로 각각 섬광결정 단면 길이의 반만큼 오프셋을 두어 접합하였다. 또한 측정된 데이터를 실제 섬광결정 영역으로 보정하기 위하여 섬광결정지도를 구했다. 결과: 평면영상을 통해 각 섬광결정들이 잘 구분되는 것을 확인할 수 있었고, 회로 개선 후 주변부의 섬광결정들이 마지막 줄까지 명백히 구분되었다. 각 섬광결정들의 에너지 분해능은 11.6%(표준편차 1.6)이었다. 결론: 본 연구에서 제안한 위치결정회로는 실험을 통해 소동물용 PET개발에 있어 만족할만한 성능을 보여주었다. 향후 더욱 정밀한 시스템을 제작하기 위해서는 다중양극 광전자증배관의 이득 불균일을 보정하기 위한 연구가 진행되어야 할 것이다.

Keywords

References

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