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ABSTRACT: This study focuses on Monte-Carlo (MC) based techniques to calculate the system matrix (SM) for iterative image reconstruction of small animal PET data. Our goal is to determine in advance if some simplifications can be done to accelerate the MC simulation without jeopardizing the accuracy of the system model. For most PET scanners, the calculation of the SM would imply extremely long simulation times, even when considering symmetries. Our small animal scanner prototype consists of a continuous LSO crystal (42 times 42 times 10 mm<sup>3 </sup>) attached to a flat panel position sensitive photomultiplier tube which was simulated using GATE. To compute the SM elements, we investigated three different radioactivity distribution models: (a) homogeneous distribution within the voxel, (b) one unique emission point at the center of the voxel and (c) eight point sources distributed within the voxel. Each of these models was simulated for five representative voxel positions inside the field of view (FOV), two of these voxels in the inner region of the FOV and the other three voxels were in the peripheral region of the FOV. The storage and discretization of the SM elements was performed by means of: (i) tube-of-response (TOR) histograms and (ii) sinograms. By comparing the SM's elements generated for each distribution model at each voxel's position, the accuracy of the models was studied. The results show that in the inner region of the FOV, model C distribution yields the best trade-off between simulation time and SM accuracy. Whereas, for the peripheral region of the FOV, model B yields the best compromise. These results are independent of the discretization process considered. Since the scanner is capable to yield depth-of-interaction (DOI) information, the study was performed taking DOI into account
Nuclear Science Symposium Conference Record, 2005 IEEE; 11/2005
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C.W. Lerche,
J.M. Benlloch,
F. Sanchez,
N. Pavon,
B. Escat, E.N. Gimenez,
M. Fernandez,
I. Torres,
M. Gimenez,
A. Sebastia,
J. Martinez
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ABSTRACT: We have studied a new and inexpensive method of measuring the depth of interaction (DOI) in γ-ray detectors with large-sized scintillation crystals. This method takes advantage of the strong correlation between the width of the undisturbed light-distribution in continuous crystals and the γ-ray's DOI. In order to quantify the dependence of the distribution's width with respect to the DOI, we first studied an analytical model of the light-distribution and tested it by means of Monte Carlo (MC) simulations of the light transport inside the crystal. Further we present an inexpensive modification of the commonly used charge division circuit that allows analog and instantaneous computation of the light-distribution's second moment without affecting the determination of the centroid. This redesigned resistor network is based on the position-sensitive proportional counter (DPC) readout and allows, together with position sensitive photo-detectors, the additional measurement of the light-distribution's standard-deviation σ. We tested the proposed circuit using the design-tool OrCAD and found the signal sufficiently large for digitalization. Finally, we conducted MC simulations of a realistic Positron Emission Tomography (PET) detector module setup that mimic a continuous Lu<sub>2</sub>SiO<sub>5</sub>:Ce<sup>3+</sup> (LSO) crystal of dimensions 40×40×10 mm<sup>3</sup> together with the new large area position-sensitive photo multiplier tube (PSPMT) H8500 from Hamamatsu. The influence of Compton scattering on the DOI determination was also estimated by MC simulations. Altogether, we obtained ≤ 5 mm DOI resolution. PACS: 87.57.Ce, 87.58.Fg, 87.62.+n, 07.85.-m.
IEEE Transactions on Nuclear Science 07/2005; · 1.45 Impact Factor
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E.N. Gimenez,
J.M. Benlloch,
M. Gimenez,
C.W. Lerche,
M. Fernandez,
N. Pavon,
M. Rafecas,
F. Sanchez,
A. Sebastia,
R. Esteve,
J.D. Martinez,
J. Toledo
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ABSTRACT: We have built a PET camera for small animals based on continuous block LSO crystals coupled to a PS-PMT flat panel. When working with continuous crystals, surface treatment is an important factor that strongly determines the main characteristics of the detector module. As a part of the work done for the development of our small animals PET camera, we have investigated the effect of the scintillator crystal surface treatment on the PET detector module performances, in order to optimize crystal configuration. We present the results for spatial resolution, image compression and energy resolution obtained when using different surface treatments in continuous LSO crystals. These results are compared with those obtained from simulations that have been carried out using DETECT2000 package.
Nuclear Science Symposium Conference Record, 2004 IEEE; 11/2004
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ABSTRACT: A design for an inexpensive depth of interaction (DOI) detector for gamma rays, suitable for nuclear medical applications, especially positron emission tomography (PET), has been developed, studied by simulations and tested experimentally. The detector consists of a continuous LSO-scintillator of dimensions 42×42×10 mm<sup>3</sup> and a new compact large-area (49×49 mm<sup>2</sup>) position sensitive photo-multiplier (PSPMT) H8500 from Hamamatsu. Since a continuous crystal is used, the scintillation light distribution is not destroyed and its first 3 moments can be used to determine the energy (0th moment), the centroids along the x- and y-direction (1st moments) and the depth of interaction (DOI), which is strongly correlated to the distribution's width and thus its standard deviation (2nd moment). The simultaneous computation of these moments allows a three-dimensional reconstruction of the position of interaction of the γ-rays within the scintillating crystal and will be realized by a modified position sensitive proportional (PSP) resistor network. No additional photo detectors or scintillating crystals are needed. According to previous Monte Carlo simulations which estimated the influence of Compton scattering for 511 keV γ-rays, the transport of the scintillation light within the detector assembly and also the behavior of the modified PSP resistor network, we expect a spatial resolution of ≲ 2 mm and a DOI resolution of ≈ 5 mm. The first experimental results presented here yield an intrinsic spatial resolution of ≲ 1.8 mm and 2.6 mm for the x- and y-direction respectively and a DOI resolution ≲ 1 cm. Further we measured an energy resolution of 12%-18%.
Nuclear Science Symposium Conference Record, 2003 IEEE; 11/2003
