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Hideo Murayama

Publications and source records attributed to Hideo Murayama.

13 recordsLinked to original sources
PubMed2006

Evaluation of static physics performance of the jPET-D4 by Monte Carlo simulations.

The jPET-D4 is the first PET scanner to introduce a unique four-layer depth-of-interaction (DOI) detector scheme in order to achieve high sensitivity and uniform high spatial resolution. This paper compares measurement and Monte Carlo simulation results of the static physics performance of this prototype research PET scanner. Measurement results include single and coincidence energy spectra, point and line source sensitivities, axial sensitivity profile (slice profile) and scatter fraction. We use GATE (Geant4 application for tomographic emission) as a Monte Carlo radiation transport model. Experimental results are reproduced well by the simulation model with reasonable assumptions on characteristic responses of the DOI detectors. In a previous study, the jPET-D4 was shown to provide a uniform spatial resolution as good as 3 mm (FHWM). In the present study, we demonstrate that a high sensitivity, 11.3 +/- 0.5%, is provided at the FOV centre. However, about three-fourths of this sensitivity is related to multiple-crystal events, for which some misidentification of the crystal cannot be avoided. Therefore, it is crucial to develop a more efficient way to identify the crystal of interaction and to reduce misidentification in order to make use of these high performance values simultaneously. We expect that effective sensitivity can be improved by replacing the GSO crystals with more absorptive crystals such as BGO and LSO. The results we describe here are essential to take full advantage of the next generation PET systems that have DOI recognition capability.

Algorithms↗
PubMed2005

Transaxial system models for jPET-D4 image reconstruction.

A high-performance brain PET scanner, jPET-D4, which provides four-layer depth-of-interaction (DOI) information, is being developed to achieve not only high spatial resolution, but also high scanner sensitivity. One technical issue to be dealt with is the data dimensions which increase in proportion to the square of the number of DOI layers. It is, therefore, difficult to apply algebraic or statistical image reconstruction methods directly to DOI-PET, though they improve image quality through accurate system modelling. The process that requires the most computational time and storage space is the calculation of the huge number of system matrix elements. The DOI compression (DOIC) method, which we have previously proposed, reduces data dimensions by a factor of 1/5. In this paper, we propose a transaxial imaging system model optimized for jPET-D4 with the DOIC method. The proposed model assumes that detector response functions (DRFs) are uniform along line-of-responses (LORs). Then each element of the system matrix is calculated as the summed intersection lengths between a pixel and sub-LORs weighted by a value from the DRF look-up-table. 2D numerical simulation results showed that the proposed model cut the calculation time by a factor of several hundred while keeping image quality, compared with the accurate system model. A 3D image reconstruction with the on-the-fly calculation of the system matrix is within the practical limitations by incorporating the proposed model and the DOIC method with one-pass accelerated iterative methods.

Brain↗
PubMed2005

[Feasibility study on a noninvasive measurement system for boron concentration.].

The kinematics of boron compounds in vivo is crucial to fully and safely utilize boron neutron capture therapy. In this paper, we proposed a prompt gamma-ray Compton scatter camera (PG-CSC), which can evaluate the 3-D kinematics of boron compounds without invasion. This PG-CSC combines a Compton camera with prompt gamma-ray analysis. The results of its design optimization and tests using simulations showed that one-hour-measurement was sufficient to evaluate a 3-D boron concentration distribution in a rat's brain with the resolution of 1 mm in FWHM.

Animals↗
PubMed2005

[2D imaging simulations of a small animal PET scanner with DOI measurement: jPET-RD.].

We present a preliminary study on the design of a high sensitivity small animal DOI-PET scanner: jPET-RD (for Rodents with DOI detectors), which will contribute to molecular imaging. The 4-layer DOI block detector for the jPET-RD that consists of scintillation crystals (1.4 mm x 1.4 mm x 4.5 mm) and a flat panel position-sensitive photomultiplier tube (52 mm x 52 mm) was previously proposed. In this paper, we investigate imaging performance of the jPET-RD through numerical simulations. The scanner has a hexagonal geometry with a small diameter and a large axial aperture. Therefore DOI information is expected to improve resolution uniformity in the whole field of view (FOV). We simulate the scanner for various parameters of the number of DOI channels and the crystal length. Simulated data are reconstructed using the maximum likelihood expectation maximization with accurate system modeling. The trade-off results between background noise and spatial resolution show that only shortening the length of crystal does not improve the trade-off at all, and that 4-layer DOI information improves uniformity of spatial resolution in the whole FOV. Excellent performance of the jPET-RD can be expected based on the numerical simulation results.

Animals↗
PubMed2004

On-clock non-paralyzable count-loss model.

This paper proposes a new count-loss model that is applicable to radiation detection systems in the field of nuclear medicine. The proposed model, represented by n = (1 - exp(-tau(n)0))/tau(n)0: input rate, n: output rate,tau: system clock duration), gives higher count rates than the well-known standard nonparalyzable (non-extensible) model represented by n = n0/(1 + tau(n)0) does, being equally simple. This model assumes that a part of the data processing is performed on a fixed system clock, requiring a data buffering function (latch) to retain digital event information temporarily, and that input timing is random. The model's simple interpretation and expression also offers an advantage over various other advanced count-loss models proposed so far. This model was found to be a better fit to a data-acquisition system for a positron emission tomography scanner.

Algorithms↗
PubMed2003

[Basic investigation of data acquisition system for next generation PET scanner].

We are under development of a 3D PET scanner with depth of interaction (DOI) capable of high sensitivity and high resolution. In this paper, we estimated the data transfer rate of data acquisition system of this PET scanner by the simulation studies. A maximum data transfer rate of coincidence pair's event information is 10 Mcps and one coincidence event is a 64-bit data format. A data acquisition system, which fulfills the specification of this scanner, is considered for parallel collection with banks including several coincidence units. Simulator of parallel collection system composed of two stand-alone simulators and the server PC. Each stand-alone simulator is composed of data generation PC, data processing circuit, SCSI and data acquisition PC. As the result of simulation studies, the maximum data transfer rate of the stand-alone simulator was 12.0 MB/s, and the maximum data transfer rates at the server PC with one and two nodes were 11.0 and 21.8 MB/s, respectively. Data transfer rate was improved by parameter optimization of a message size and multi-processing of data acquisition software using RAM-DISK.

Computer Simulation↗
PubMed2003

[Computer simulation of DOI-PET detector (1) -analysis of DOI discrimination accuracy in a detector block-].

A detector proposed by Murayama et al. for detection of depth-of-interaction (DOI) in PET consists of three-dimensionally arranged crystal elements with proper optical reflectors and is coupled to an array of photomultiplier tubes. This detector has a great advantage in easiness and cost in fabrication. We implemented a simulator of this detector that allows us to find appropriate values of parameters such as optical properties of crystal or detector unit geometry before making detectors. The simulator is based on the Monte Carlo method that traces the migration of optical photons generated by interaction of a gamma ray with crystal. First, the simulator performance was validated by comparing with the experimental data obtained with some prototype detectors. Then, on some parameters including refractive index of inter-crystal material, reflectance of optical reflector and detector geometry, appropriate values were investigated for accurate discrimination of crystal element of interaction.

Computer Simulation↗
PubMed2002

Shielding effects of body - shields for 3D PET.

We analyzed basic physics characteristics of body-shields which have been considered for screening out radioactivity outside the field of view (OFOV) in positron emission tomography (PET). Phantom experiments were performed with simple rectangular body-shields. A Monte Carlo simulation technique was used to analyze the experimental results and to simulate cases that were not examined experimentally. It was confirmed that the body-shields effectively reduced unwanted radiations from OFOV radioactivity for one of the latest commercial PET scanners, the ECAT EXACT HR(+). The geometrical conditions were the most important factor in determining the shielding effect. The shield thickness should be large enough to keep the shield-scatter component low. The body-shield should be carefully designed to minimize the gap between the body-shield and radioactive distribution as much as possible to maximize the shielding effects, and to be applicable to clinical diagnoses.

Equipment Design↗
PubMed2001

[Algebraic 2D PET image reconstruction using depth-of-interaction information]

Recently a high-performance PET scanner, which measures depth-of-interaction (DOI) information, is being developed for molecular imaging. DOI measurement of multi-layered thin crystals can improve spatial resolution and scanner sensitivity simultaneously. In this paper, we apply an algebraic image reconstruction method to 2-dimensional (2D) DOI-PET scanners using accurate system modeling, in order to evaluate the effects of using DOI information on PET image quality. Algebraic image reconstruction methods have been successfully used to improve PET image quality, compared with the conventional filtered backprojection method. The proposed method is applied to simulated data for a small 2D DOI-PET scanner. The results show that accurate system modeling improves spatial resolution without noise emphasis, and that DOI information improves uniformity of spatial resolution.

Journal Article↗
PubMed2001

Monte Carlo simulation for PET scanners and shields.

A Monte Carlo simulation code was developed for simulating PET scanners with the Monte Carlo program package GEANT. The present simulation code can handle not only conventional types of PET scanners, but also any complex detector systems with arbitrary geometrical configuration. All the relevant interactions of photons and electrons are taken into account in all the defined objects while optical tracking in the scintillation crystals is approximated by simple analytical simulation. In addition to basic PET scanner performance factors, such as sensitivity and scatter fraction, valuable but un-measurable information, such as photon trajectories and interaction position distribution, can be obtained and represented graphically in various ways. This simulation code has proved useful in analyzing the physics characteristics of existing commercial PET scanners and related shields, and in design studies of new PET scanners.

Journal Article↗