A Four-Layer DOI Detector With a Relative Offset for Use in an Animal PET System

Mikiko Ito,Jae Sung Lee,Sun Il Kwon,Geon Song Lee,Byungsik Hong,Kyong Sei Lee,Kwang-Souk Sim,Seok Jae Lee,June Tak Rhee,Seong Jong Hong IEEE 2010 IEEE transactions on nuclear science Vol.57 No.3

<P>For animal PET systems to achieve high sensitivity without adversely affecting spatial resolution, they must have the ability to measure depth-of-interaction (DOI). In this paper, we propose a novel four-layer PET system, and present the performances of modules built to verify the concept of the system. Each layer in the four-layer PET system has a relative offset of half a crystal pitch from other layers. Performances of the four-layer detector were estimated using a GATE Monte Carlo simulation code. The proposed system consists of six H9500 PMTs, each of which contains 3193 crystals. A sensitivity of 11.8% was obtained at the FOV center position of the proposed system. To verify the concept, we tested a PET module constructed using a H9500 flat panel PMT and LYSO crystals of cross-sectional area 1.5 × 1.5 mm<SUP>2</SUP>. The PET module was irradiated with a 1.8 MBq <SUP>22</SUP>Na radiation source from the front or side of the crystals to obtain flood images of each crystal. Collimation for side irradiation was achieved using a pair of lead blocks of dimension 50 × 100 × 200 mm<SUP>3</SUP>. All crystals in the four layers were clearly identified in flood images, thus verifying the DOI capability of the proposed four-layer PET system. We also investigated the optimal combination of crystal lengths in the four-layer PET system using the GATE Monte Carlo simulation code to generate events from simulated radiation sources, and using the ML-EM algorithm to reconstruct simulated radiation sources. The combination of short crystal lengths near radiation sources and long crystal lengths near the PMT provides better spatial resolution than combinations of same crystal lengths in the four-layer PET system.</P>

Design and simulation of a novel method for determining depth-of-interaction in a PET scintillation crystal array using a single-ended readout by a multi-anode PMT

Ito, Mikiko,Lee, Jae Sung,Park, Min-Jae,Sim, Kwang-Souk,Hong, Seong Jong Institute of Physics in association with the Ameri 2010 Physics in medicine & biology Vol.55 No.13

<P>PET detectors with depth-of-interaction (DOI) encoding capability allow high spatial resolution and high sensitivity to be achieved simultaneously. To obtain DOI information from a mono-layer array of scintillation crystals using a single-ended readout, the authors devised a method based on light spreading within a crystal array and performed Monte Carlo simulations with individual scintillation photon tracking to prove the concept. A scintillation crystal array model was constructed using a grid method. Conventional grids are constructed using comb-shaped reflector strips with rectangular teeth to isolate scintillation crystals optically. However, the authors propose the use of triangularly shaped teeth, such that scintillation photons spread only in the <I>x</I>-direction in the upper halves of crystals and in the <I>y</I>-direction in lower halves. DOI positions can be estimated by considering the extent of two-dimensional light dispersion, which can be determined from the multiple anode outputs of a position-sensitive PMT placed under the crystal array. In the main simulation, a crystal block consisting of a 29 × 29 array of 1.5 mm × 1.5 mm × 20 mm crystals and a multi-anode PMT with 16 × 16 pixels were used. The effects of crystal size and non-uniform PMT output gain were also explored by simulation. The DOI resolution estimated for 1.5 × 1.5 × 20 mm<SUP>3</SUP> crystals was 2.16 mm on average. Although the flood map was depth dependent, each crystal was well identified at all depths when a corner of the crystal array was irradiated with 511 keV gamma rays (peak-to-valley ratio ∼9:1). DOI resolution was better than 3 mm up to a crystal length of 28 mm with a 1.5 × 1.5 mm<SUP>2</SUP> or 2.0 × 2.0 mm<SUP>2</SUP> crystal surface area. The devised light-sharing method allowed excellent DOI resolutions to be obtained without the use of dual-ended readout or multiple crystal arrays.</P>

Positron Emission Tomography (PET) Detectors with Depth-of- Interaction (DOI) Capability

Mikiko Ito,홍성종,이재성 대한의용생체공학회 2011 Biomedical Engineering Letters (BMEL) Vol.1 No.2

Because positron emission tomography (PET) provides biochemical information in vivo with the sensitivity at the sub-pico-molar level, pre-clinical research using PET plays an important role in biological and pharmaceutical sciences. However, small animal imaging by PET has been challenging with respect to spatial resolution and sensitivity due to the small volume of the imaging objects. A DOI-encoding technique allows for pre-clinical PET to simultaneously achieve high spatial resolution and high sensitivity. Thus many DOI-encoding methods have been proposed. In this paper we describe why DOI measurements are important, what is required in DOI-encoding designs, and how to extract DOI information in scintillator-based DOI detectors. Recently, there has been a growing interest in DOI measurements for TOF PET detectors to correct time walk as a function of DOI position. Thus, the DOI-encoding method with a high time performance suitable for TOF detectors is now required. The requirements to improve the time resolution in DOI detectors are discussed as well.

Design Optimization of a Small-animal SPECT System Using LGSO Continuous Crystals and Micro Parallel-hole Collimators

김중현,Mikiko Ito,김수미,홍성종,이재성 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.1

A small-animal single photon emission computed tomography (SPECT) system having compact size and low cost was designed using monolithic LGSO scintillation crystals and micro parallel-hole collimators through Monte Carlo simulations. A spatial resolution of 1 mm and a sensitivity of 100 cps/MBq were achieved with a four-head SPECT system. A hot rod with a diameter of 1.0 mm was resolved in the SPECT image of the ultra-micro hot spot phantom. Using a thin monolithic crystal and micro collimator, we achieved high spatial resolution and high sensitivity.

Unreduced Gamete Formation in Two Cymbidium pumilum F₁ Hybrids

Juntaro Kato,Mikiko Tomiyasu,Katumi Nakashima,Yuuichi Futagami,Tatsuya Oguri,Hiroshi Ito,Syoichi Ichihashi 한국원예학회 2006 한국원예학회 기타간행물 Vol.- No.-

Evaluation of a Fast Photomultiplier Tube for Time-of-Flight PET

이재성,이진표,Mikiko Ito 대한의용생체공학회 2011 Biomedical Engineering Letters (BMEL) Vol.1 No.3

Purpose Adding time-of-flight (TOF) information to positron emission tomography (PET) can lead to an improvement in image quality because TOF information allows the estimation of gamma ray annihilation positions in three dimensions. For accurate position estimation, precise time resolution is the most important characteristic required of TOF-PET detectors. The aims of this study were to establish the optimal setup for timing measurements and to evaluate the timing performance of a fast photomultiplier tube (PMT) (Hamamatsu R9800)coupled with a lutetium yttrium orthosilicate (LYSO)scintillation crystal for TOF-PET detector development. Methods Performance of a fast PMT (diameter, 25 mm;length, 55 mm) coupled with a LYSO crystal (4 × 4 × 10mm3) was measured in coincidence experiments with 511 keV annihilation photons from a 22Na gamma source. Timing measurement optimization was carried out with a leadingedge discriminator (LED) and a constant fraction discriminator (CFD). Results Results showed the optimal timing resolution could be obtained with a CFD time delay of 1 ns; timing resolutions (FWHM) of the LYSO crystal-coupled fast PMT were measured to be 198 and 254 ps for two different R9800PMTs. The energy resolutions at 511 keV were 10.8% and 10.6%, respectively. Additional experiments to determine the position uncertainty were performed at three different source positions and the position uncertainty (FWHM) in the TOF measurement using these PMTs was estimated to be 4.50 cm. Conclusions The performance of fast R9800 PMT coupled with a LYSO crystal showed good potential for development as a TOF-PET detector module.

Nurses’ Experiences of End-of-life Care in Long-term Care Hospitals in Japan: Balancing Improving the Quality of Life and Sustaining the Lives of Patients Dying at Hospitals

Ryo Odachi,Tomoko Tamaki,Mikiko Ito,TaTaketoshi Okita,Yuri Kitamura,Tomotaka Sobue 한국간호과학회 2017 Asian Nursing Research Vol.11 No.3

Purpose: In Japan, about 80% of deaths occur in hospitals, especially long-term care beds. The purpose of this study was to clarify the nursing practices used for such older patients at the end-of-life stage in longtermcare wards via the modified grounded theory approach (M-GTA). Methods: Data were obtained through semi-structured interviews of nineteen nurses working in cooperating long-term care wards, acute care wards, or hospice services (to allow for constant comparison between these types of wards) in western Japan in 2014. We analyzed the transcribed data using M-GTA. Results: The core category that emerged from the analysis was “Balancing enhancement of patients' daily life quality and life-sustaining care in the face of uncertainty about the patients' character.” Eleven categories emerged, such as Seeking older patients' character with their family, Supporting families' decision making, Rebuilding patients' daily life in the ward, and Sustaining patients' life span through medical care. Conclusions: Nurses experienced uncertainty about the care needs of older patients, the ethical problems of Enhancing the patients' QOL by using risky care, and the evaluation criteria used to judge their own nursing care after the patients' death. All nurses had the goal of ensuring a natural death for all patients. Nurses' acceptance and evaluation of their own care was critically influenced by the patient's family's responses to their care after patients' death. Further research is necessary to develop evaluation criteria and educational programs for end-of-life nursing care of older adults.

Depth of Interaction (DOI) Determination in Three-Layer Small Animal PET

( Sun Il Kwon ),( Seong Jong Hong ),( Mikiko Ito ),( Geon Song Lee ),( Kwang Souk Sim ),( Kwang Suk Park ),( Jung Tak Rhee ),( Jae Sung Lee ) 대한핵의학회 2007 핵의학 분자영상 Vol.41 No.5

SPATIAL AND ENERGY RESOLUTIONS OF A HEXAGONAL ANIMAL PET SCANNER BASED ON LGSO CRYSTAL AND FLAT-PANEL PMT

CHAN MI LEE,홍성종,HYUN SUK YOON,Mikiko Ito,SUN IL KWON,SANG KEUN PARK,이동수,Kwang Souk Sim,이재성 한국원자력학회 2012 Nuclear Engineering and Technology Vol.44 No.1

The aim of this study was to explore the spatial and energy resolutions of a PET scanner that we have recently developed. The scanner, which consists of six detector modules with 1-layer LGSO crystals, has a hexagonal configuration with a faceto-face distance of 86.4 mm between two opposite PET modules; such properties facilitate the imaging of small animals. A 22Na point source was employed to estimate horizontal and vertical spatial resolutions. To assess the energy resolution, a uniform 18F cylindrical phantom was scanned. A software-based spectrum analysis of list-mode data was used to assign a local energy window centered on the photopeak position for every single crystal. For the image reconstruction, an ML-EM algorithm was used. The spatial resolutions at the center of the scanner were 0.99 mm in the horizontal direction and 1.13mm in the vertical direction. The energy resolution averaged over each PMT ranged from 13.3%-14.3%, which gave an average value of 13.8%. These results show that this simple system is promising for small animal imaging with excellent spatial and energy resolutions.

Concept Verification of Three-Layer DOI Detectors for Small Animal PET

Hong, Seong Jong,Kwon, Sun Il,Ito, Mikiko,Lee, Geon Song,Sim, Kwang-Souk,Park, Kwang Suk,Rhee, June Tak,Lee, Jae Sung IEEE 2008 IEEE transactions on nuclear science Vol.55 No.3

<P> Improved spatial resolution without sacrificing sensitivity is one of the most challenging developmental goals for small animal PET scanners. The 3-layer configuration that we propose here utilizes relative offsets of half a crystal pitch in x- and y-directions, and pulse shape discrimination to obtain depth of interaction (DOI). Three layers of crystals with a dimension 1.5<TEX>$\,\times\,$</TEX>1.5<TEX>$\,\times\,$</TEX>7.0mm <TEX>$^{3}$</TEX> were composed of a L <TEX>$_{0.2}$</TEX> GSO (Lu<TEX>$_{0.4}$</TEX> Gd<TEX>$_{1.6}$</TEX> SiO<TEX>$_{4}$</TEX>: Ce) crystal layer and a L<TEX>$_{0.9}$</TEX> GSO (Lu<TEX>$_{1.8}$</TEX> Gd <TEX>$_{0.2}$</TEX> SiO<TEX>$_{4}$</TEX> : Ce) crystal layer aligned with each other, and a L <TEX>$_{0.9}$</TEX> GSO crystal layer offset at half a crystal pitch in x- and y-directions. The L<TEX>$_{0.9}$</TEX> GSO crystal layer was attached to a Hamamatsu H9500 flat-panel PMT. The devised small animal PET scanner has a diameter of 84 mm with one detector ring, and can be upgraded to two detector rings. GEANT4 Monte-Carlo simulation was used to estimate sensitivities of <TEX>$\sim 12\hbox{\%}$</TEX> and <TEX>$\sim 20\hbox{\%}$</TEX>, respectively, at the center of one and two PMT ring system with an energy window of 350 <TEX>$\sim$</TEX> 750 keV. We present flood images with peak-to-valley ratios of about 5–6 obtained using <TEX>$^{22}$</TEX> Na and layer identification capability of <TEX>$\sim 99\hbox{\%}$</TEX> with pulse shape analysis, and verified the basic concepts of multi-layer small animal PET. </P>