My Abstract List

M. Hamamoto¹, H. Murayama², N. Inadama², T. Tsuda³, Y. Ono³, T. Yamaya², E. Yoshida², K. Shibuya², F. Nishikido¹, J. Kikuchi¹, T. Doke¹

¹Science and Engineering, Waseda university, Tokyo, Japan
²National Institute of Radiological Sciences, Chiba, Japan
³Science and Technology, Chiba University, Chiba, Japan

An 8-layer depth of interaction (DOI) detector was designed on the basis of pulse shape discrimination (2-layer DOI encoding) and the proper reflector arrangement (4-layer DOI encoding), and its capability was proved with a prototype 8-layer (2 × 4) DOI detector. The proper reflector arrangement controls light path in the crystal array and makes 4-layer DOI detection. Pulse shape discrimination then makes DOI detection to 8. The prototype DOI detector was composed of 8 layers of 10 × 10 Gd₂SiO₅ (GSO) crystal array and a 256-channel flat panel position sensitive photomultiplier tube (256ch FP-PMT) which has 16 × 16 multi anodes at intervals of 3.04 mm. The size of a crystal element is 2.90 mm × 2.90 mm × 3.75 mm. Two kind GSO crystals were used; GSO crystals of 0.5 mol% Ce dopant were in the 1st, the furthest from the FP-PMT, 3rd, 5th, and 7th layers and crystals of 1.5 mol% Ce dopant were in other layers. Performance of the 8-layer DOI detector was evaluated by irradiating 662 keV uniform gamma rays. In this measurement, it is found that all crystals could be identified clearly.

J03-28: Measurement of 32 × 8 × 4 LYSO Crystal Responses of DOI Detector for jPET-RD

T. Tsuda^1,2, H. Murayama², K. Kitamura^2,3, N. Inadama², T. Yamaya², E. Yoshida², F. Nishikido⁴, M. Hamamoto^2,4, H. Kawai⁵, Y. Ono^1,2

¹Graduate School of Science and Technology, Chiba University, Chiba-shi, Chiba, Japan
²National Institute of Radiological Sciences, Chiba-shi, Chiba, Japan
³Shimadzu Corporation, Kyoto, Japan
⁴School of Science and Engineering, Waseda University, Tokyo, Japan
⁵Faculty of Science, Chiba University, Chiba-shi, Chiba, Japan

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 Lu_2(1-x)Y_2xSiO₅ (LYSO). In this work, we measured response functions of a jPET-RD prototype detector composed of four layers of a 32 (axial) × 8 (transaxial) LYSO (Lu: 98%, Y: 2%) crystal block with 511 keV gamma rays to estimate resolution performance. The size of each crystal element is 1.44 mm × 1.44 mm × 4.5 mm. The crystal block (46.5 mm × 11.6 mm × 18.0 mm) is placed on the central area of a 256-channel flat panel position sensitive photomultiplier tube (49 mm × 49 mm useful area) and coupled with silicone rubber. As a result, the averaged FWHM of response functions was 1.56 mm in axial and 4.51 mm in depth direction. The energy resolution of all events was 14.7% and the time resolution was found to be 0.66 ns. The experimental results promise excellent performance of a jPET-RD detector.

M03-115: DOI Detection Capability of 3D Crystal Array Standing over Two PMTs

N. Inadama¹, H. Murayama¹, T. Yamaya¹, T. Tsuda^1,2, Y. Ono^1,2, M. Hamamoto^1,3

¹Medical Physics, National Institute of Radiological Sciences, Chiba, Japan
²Graduate School of Science and Technology, Chiba University, Chiba, Japan
³Science and Engineering, Waseda university, Tokyo, Japan

No scintillation crystal in the region between adjacent PMTs, PMT blind region, will cause loss of data sampling and less sensitivity in the system.
We propose design of a depth of interaction (DOI) detector to fill up the PMT blind region with crystals. In the design, a 3-dimensional (3D) array of single kind crystals stands on two PMTs. The crystal array is optically coupled to the PMTs directly and to control scintillation light path in the DOI crystal array, materials between crystal elements are chosen among optical film, grease, and just remained as air gap instead of coupling a light guide on the bottom of the array as is generally done. Not only reflector but translucent film is also utilized as optical film in the DOI detector design. In this paper, a 2-layer DOI crystal array is demonstrated. It is developed with the intention of the use in jPET-RD system; the PET system we plan to develop for small animals. There is about 6 mm interval in axial direction between outer anodes of adjacent two PMTs. The cross section of the crystal elements is 1.44 mm × 1.44 mm in jPET-RD detector so that 2-layers of four crystals are in the PMT blind region. We introduce the design of the 2-layer DOI crystal array and the results of its performance estimation.

M03-244: Motion Correction for jPET-D4: Improvement of Measurement Accuracy with a Solid Marker

T. Hasegawa¹, Y. Fukushima¹, H. Muraishi¹, T. Nakano¹, T. Kuribayashi¹, Y. Shiba¹, K. Maruyama¹, T. Yamaya², E. Yoshida², N. Hagiwara³, T. Obi³, H. Murayama²

¹Allied Health Sciences, Kitasato University, Kitasato 1-15-1, Sagamihara, Kanagawa, Japan
²Medical Physics, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage, Chiba, Japan
³Information Processing, Tokyo Institute of Technology, Midoriku, Yokohama, Japan

The jPET-D4 is a high-resolution and high-sensitivity PET scanner that is dedicated for brain imaging. In order to avoid deterioration of spatial resolution due to the patient motion, and also to reduce mental and physical stress of the patient, there is a need of motion detection and correction. We proposed a new motion detection method with a solid marker that was specially designed to enable position and angle (direction) measurement with one optical movie camera. An advantage of this method over a conventional method is that it is applicable to long narrow patient port spaces. Measurement accuracy was and will be significantly improved to be better than 0.2 mm in the positions and 0.3 deg in the angles (standard deviation) by refining the solid marker, in particular, about machining accuracy. In addition, we have been developing a model to calculate the axial position from measured parameters. As a result of multivariate analysis on measured motion tracking data, we found that a sufficient accuracy can be obtained under experimental conditions. For motion correction in jPET-D4, attaching methods, device installation, and correction algorithms are under consideration and development.

M03-304: Event-by-Event Random and Scatter Estimator Based on Support Vector Machine Using Multi-Anode Outputs

E. Yoshida¹, Y. Kimura², K. Kitamura^3,1, F. Nishikido⁴, T. Yamaya¹, H. Murayama¹

¹National Institute of Radiological Sciences, Chiba, Japan
²Tokyo Metropolitan Institute of Gerontology, Tokyo, Japan
³Shimadzu Corporation, Kyoto, Japan
⁴Waseda University, Tokyo, Japan

In PET, an incident angle of gamma ray is estimated from a coincidence information, but coincidence events are contaminated with random and scatter components. The mean contribution to the image from these components can be measured or estimated, but the noise resulting from the statistical variations in the detected events still remains and decreases noise equivalent count rates (NECR). Theoretically, incident angle to detectors or other related information can be used to discriminate random and scatter events from true events for increasing the NECR. These information can be delineated from spatial distributions of deposit energies on multi-anode PMTs, which arise from inter-crystal scattering and vary with the coincidence event type (true or random/scatter). In this work, a novel method for random and scatter subtraction has been developed using a recently developed and widely used statistical pattern recognition scheme of the support vector machine (SVM). Input data is a pair of spatial distributions of 256 outputs of multi-anode PMTs from coincidence detectors. SVM was trained by coincidence events generated from a detector simulator using Monte Carlo calculation. The simulation study showed the proposed method was applicable for event-by-event estimation of scatter and random coincidence.

¹Department of Medical Physics, National Institute of Radiological Science, Chiba 263-8555, Japan
²Department of Applied Chemistry, Tohoku University, Sendai 980-8579, Japan

An idea for developing scintillators possessing both a large light output and a quick response is presented. Usually, some direct-gap semiconductors exhibit sub-nanosecond decaying ultra-fast scintillation only at a very low temperature. The authors found that the thermal quenching is effectively prevented by a construction of a low-dimensional quantum confinement system, and practical light output can be obtained even at room temperature. A comparative study in scintillation properties of two- and three-dimensional semiconducting materials having similar compositions was demonstrated, and physical effects of the quantum confinement systems are discussed.
A crystals of (C₆H₁₃NH₃)₂PbI₄ having a multiple quantum well structure exhibited three decay components of 390 ps, 3.8 ns and 16 ns with the ratios of 28%, 29% and 43%, respectively. And the total light output at 300 K was 11% of that of NaI:Tl.

M07-83: (premium) The jPET-D4: Imaging Performance of the 4-Layer Depth-of-Interaction PET Scanner

T. Yamaya¹, E. Yoshida¹, M. Satoh¹, T. Tsuda^2,1, K. Kitamura^3,1, T. Obi⁴, T. Hasegawa⁵, H. Haneishi⁶, N. Inadama¹, S. Tanada⁷, H. Murayama¹

¹Department of Medical Physics, National Institute of Radiological Sciences, Chiba, Japan
²Graduate School of Science and Technology, Chiba University, Chiba, Japan
³Medical Systems Division, Shimadzu Corporation, Kyoto, Japan
⁴Graduate School of Science and Technology, Tokyo Institute of Technology, Yokohama, Japan
⁵Allied Health Sciences, Kitasato University, Sagamihara, Japan
⁶Research Center for Frontier Medical Engineering, Chiba University, Chiba, Japan
⁷Department of Medical Imaging, National Institute of Radiological Sciences, Chiba, Japan

The jPET-D4 is a high-performance brain PET scanner which achieves not only high spatial resolution but also high scanner sensitivity by discriminating 4-layer depth-of-interaction (DOI) information. The scanner is designed to have 5 rings of 24 detector blocks each, and the detector block consists of 1,024 GSO crystals of 2.9 mm × 2.9 mm × 7.5 mm, which are arranged in 4 layers of 16 × 16 arrays. At this stage, one of the 5 block-detector rings has been assembled into the jPET-D4 gantry. In this paper, we investigate the imaging performance of the jPET-D4 prototype. In order to reduce computational cost while keeping the advantage of DOI information in iterative image reconstruction, we have proposed the DOI compression (DOIC) method which reduces data dimensions with suppressing resolution loss. We have also proposed an imaging system model optimized for the jPET-D4 which enables fast system matrix calculation while preserving image quality. These methods were applied to the real data of needle sources on a uniform background. The result shows that almost uniform spatial resolution of less than 3 mm is obtained over the field-of-view by using the 4-layer DOI information. The Hoffman 3D brain phantom was also measured to compare the jPET-D4 with the HR+ commercial scanner. The result clearly shows the excellent imaging performance of the jPET-D4. Two or more detector-rings are being assembled, and the first volunteer tests are being planned.

M11-111: The jPET-D4: Simple and Reliable Construction Method for 4-Layer DOI Crystal Blocks

Y. Ono^1,2, H. Murayama², T. Yamaya², H. Kawai³, N. Inadama², T. Tsuda^1,2, M. Hamamoto^2,4

¹Graduate School of Science and Technology, Chiba University, Chiba, Japan
²National Institute of Radiological Sciences, Chiba, Japan
³Faculty of Science, Chiba University, Chiba, Japan
⁴Science and Engineering, Waseda university, Tokyo, Japan

The jPET-D4 detector module consists of four layers of 16 by 16 Gd₂SiO₅ (GSO) crystals and a 256 channel flat panel position sensitive photomultiplier tube (256ch FP-PMT). Two kinds of GSO crystals having different Ce dopant concentration are used in the upper and lower two layers in order to distinguish the DOI using pulse shape discrimination. Proper reflector insertion in the crystal block enables to identify crystals of detection in each two layers. For mass production of the DOI crystal block composed of 1024 crystal elements with proper reflector arrangement, we designed appropriate tools which promote simple construction as well as uniform configuration. The four of crystal layer assembled with the tool are coupled in depth by RTV rubber and adjusted external size with another tool. The construction took only 3 hours per one crystal block. To estimate reliability of the construction method, uniformity of pulse shape discrimination, energy resolution and light output were studied on 24 crystal blocks actually constructed in the method. The results show that the averaged energy resolutions for the 1st, 2nd, 3rd and 4th-layer are 16.0 ± 1.2%, 15.7 ± 0.9%, 17.5 ± 1.0% and 17.9 ± 1.5%, respectively. Light output uniformity among four layers is kept within 3% over 24 crystal blocks.

M11-270: The jPET-D4: Detector Calibration and Acquisition System of the 4-Layer DOI-PET Scanner

E. Yoshida¹, T. Yamaya¹, M. Watanabe², N. Inadama¹, T. Tsuda^3,1, K. Kitamura^4,1, T. Hasegawa⁵, T. Obi⁶, H. Haneishi³, H. Murayama¹

¹National Institute of Radiological Sciences, Chiba, Japan
²Hamamatsu Photonics K.K., Shizuoka, Japan
³Chiba Univercity, Chiba, Japan
⁴Shimadzu Corporation, Kyoto, Japan
⁵Kitasato Univercity, Kanagawa, Japan
⁶Tokyo Institute of Technology, Kanagawa, Japan

A high-performance brain DOI-PET scanner, jPET-D4, is under development. This scanner is designed to achieve not only high spatial resolution but also high sensitivity using four-layered DOI detectors. The scanner has five-detector rings with the ring diameter of 390 mm and each detector ring consists of 24 DOI detectors. In order to identify the crystal of interaction and its energy from PMT output, we have previously proposed the DOI detector calibration method. This method creates position and energy Look-Up-Tables (LUTs) from the uniform irradiation. The position LUT converts location of 2D position histograms to crystal address. The energy LUT corrects light output of each crystal. At this stage, one of five detector rings has been installed and calibrated. The average energy resolution for 24 DOI detectors was optimized up to 17 % ± 1 %. Full detector rings are being mounted on the gantry in stages.

M11-321: Evaluation of Error on Parameter Estimates in the Quantitative Analysis of Receptor Studies with Positron Emission Tomography

Y. Ikoma¹, H. Ito¹, T. Yamaya², K. Kitamura³, A. Takano¹, H. Toyama⁴, T. Suhara¹

¹Brain Imaging Project, National Institute of Radiological Sciences, Chiba, Japan
²Department of Medical Physics, National Institute of Radiological Sciences, Chiba, Japan
³Medical Systems Division, Shimadzu Corporation, Kyoto, Japan
⁴Department of Health Service Management, International University of Health and Welfare, Ohtawara, Tochigi, Japan

Quantification of in vivo tracer studies has been performed with PET to assess the binding potential (BP) of the receptor in the human brain. In the quantitative analysis, the error of parameter estimates is affected by the noise depends on the collected count, and the reliability of estimated kinetic parameter is important for the assessment of the BP. However, the evaluation of the reliability is not easy for human data because the true noise level is not precisely known. In this study, we have developed a method for estimating the reliability of determination of parameter in human data from the residual error obtained in the compartment model analysis, and applied for evaluating the influence of ROI size on the reliability of parameter estimates. As a result, the reliability of kinetic parameter estimates for human data was able to be deduced from the simulation data in which the noise was similar to human data, and the variation of estimated BP became smaller as the ROI size became larger. On account of the anatomical volume of the target region, there is a limit to the ROI size. Therefore, for the ligand with high error of parameter estimates, it is necessary to make up for a deficiency of count by improvement in sensitivity of the system or increase of the injection dose. With our method, the reliability of parameter estimates will be able to be estimated easily for various conditions, such as the injection dose, kinetic parameter, and sensitivity of the PET system.

Abstracts of the jPET Project Members in IEEE NSS & MIC 2005

JOINT: 2, MIC: 7, NSS: 1.
Oral: 2, Poster: 8 (including 1 PREMIUM).

Abstracts of the jPET Project Members in IEEE NSS & MIC 2005

JOINT: 2, MIC: 7, NSS: 1. Oral: 2, Poster: 8 (including 1 PREMIUM).

JOINT: 2, MIC: 7, NSS: 1.
Oral: 2, Poster: 8 (including 1 PREMIUM).