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ABSTRACT: We are developing a three-dimensional (3D) position-sensitive detector with isotropic spatial resolution, the X'tal cube. Originally, our design consisted of a crystal block for which all six surfaces were covered with arrays of multi-pixel photon counters (MPPCs). In this paper, we examined the feasibility of reducing the number of surfaces on which a MPPC array must be connected with the aim of reducing the complexity of the system. We evaluated two kinds of laser-processed X'tal cubes of 3 mm and 2 mm pitch segments while varying the numbers of the 4 × 4 MPPC arrays down to two surfaces. The sub-surface laser engraving technique was used to fabricate 3D grids into a monolithic crystal block. The 3D flood histograms were obtained by the Anger-type calculation. Two figures of merit, peak-to-valley ratios and distance-to-width ratios, were used to evaluate crystal identification performance. Clear separation was obtained even in the 2-surface configuration for the 3 mm X'tal cube, and the average peak-to-valley ratios and the distance-to-width ratios were 6.7 and 2.6, respectively. Meanwhile, in the 2 mm X'tal cube, the 6-surface configuration could separate all crystals and even the 2-surface case could also, but the flood histograms were relatively shrunk in the 2-surface case, especially on planes parallel to the sensitive surfaces. However, the minimum peak-to-valley ratio did not fall below 3.9. We concluded that reducing the numbers of MPPC readout surfaces was feasible for both the 3 mm and the 2 mm X'tal cubes.
Physics in Medicine and Biology 02/2013; 58(5):1361-1374. · 2.83 Impact Factor
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Tomoyuki Hasegawa,
Keiichi Oda,
Yasuhiro Wada,
Toshiaki Sasaki,
Yasushi Sato,
Takahiro Yamada,
Mikio Matsumoto, Hideo Murayama,
Kei Kikuchi,
Hiroki Miyatake,
Yutaka Abe,
Kenta Miwa,
Kenta Akimoto,
Kei Wagatsuma
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ABSTRACT: OBJECTIVE: To improve the reliability and convenience of the calibration procedure of positron emission tomography (PET) scanners, we have been developing a novel calibration path based on traceable point-like sources. When using (22)Na sources, special care should be taken to avoid the effects of 1.275-MeV γ rays accompanying β (+) decays. The purpose of this study is to validate this new calibration scheme with traceable point-like (22)Na sources on various types of PET scanners. METHOD: Traceable point-like (22)Na sources with a spherical absorber design that assures uniform angular distribution of the emitted annihilation photons were used. The tested PET scanners included a clinical whole-body PET scanner, four types of clinical PET/CT scanners from different manufacturers, and a small-animal PET scanner. The region of interest (ROI) diameter dependence of ROI values was represented with a fitting function, which was assumed to consist of a recovery part due to spatial resolution and a quadratic background part originating from the scattered γ rays. RESULTS: The observed ROI radius dependence was well represented with the assumed fitting function (R (2) > 0.994). The calibration factors determined using the point-like sources were consistent with those by the standard cross-calibration method within an uncertainty of ±4 %, which was reasonable considering the uncertainty in the standard cross-calibration method. CONCLUSION: This novel calibration scheme based on the use of traceable (22)Na point-like sources was successfully validated for six types of commercial PET scanners.
Annals of Nuclear Medicine 02/2013; · 1.50 Impact Factor
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ABSTRACT: The X'tal cube is a depth-of-interaction (DOI)-PET detector which is aimed at obtaining isotropic resolution by effective readout of scintillation photons from the six sides of a crystal block. The X'tal cube is composed of the 3D crystal block with isotropic resolution and arrays of multi-pixel photon counters (MPPCs). In this study, to fabricate the 3D crystal block efficiently and precisely, we applied a sub-surface laser engraving (SSLE) technique to a monolithic crystal block instead of gluing segmented small crystals. The SSLE technique provided micro-crack walls which carve a groove into a monolithic scintillator block. Using the fabricated X'tal cube, we evaluated its intrinsic spatial resolution to show a proof of concept of isotropic resolution. The 3D grids of 2 mm pitch were fabricated into an 18 × 18 × 18 mm(3) monolithic lutetium yttrium orthosilicate (LYSO) crystal by the SSLE technique. 4 × 4 MPPCs were optically coupled to each surface of the crystal block. The X'tal cube was uniformly irradiated by (22)Na gamma rays, and all of the 3D grids on the 3D position histogram were separated clearly by an Anger-type calculation from the 96-channel MPPC signals. Response functions of the X'tal cube were measured by scanning with a (22)Na point source. The gamma-ray beam with a 1.0 mm slit was scanned in 0.25 mm steps by positioning of the X'tal cube at vertical and 45° incident angles. The average FWHM resolution at both incident angles was 2.1 mm. Therefore, we confirmed the isotropic spatial resolution performance of the X'tal cube.
Radiological Physics and Technology 07/2012;
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ABSTRACT: PurposeThus far, cylindrical phantoms with 18F or 68Ge/68Ga have been used in the standard techniques for determining the cross-calibration factors (CCFs) of PET scanners. This paper PurposeThus far, cylindrical phantoms with 18F or 68Ge/68Ga have been used in the standard techniques for determining the cross-calibration factors (CCFs) of PET scanners. This paper
describes a new practical method that uses a point-like 22Na radioactive source for determining CCFs. describes a new practical method that uses a point-like 22Na radioactive source for determining CCFs.
MethodsA point-like 22Na radioactive source (about 700kBq) was equipped with a spherical aluminium absorber capsule to ensure the symmetry of the MethodsA point-like 22Na radioactive source (about 700kBq) was equipped with a spherical aluminium absorber capsule to ensure the symmetry of the
emitted photons. During measurements, the source was moved in the axial direction to cover the whole axial field of view (FOV) emitted photons. During measurements, the source was moved in the axial direction to cover the whole axial field of view (FOV)
of a clinical PET scanner, SET-2400W. The region-of-interest (ROI) values obtained in reconstructed images without scatter of a clinical PET scanner, SET-2400W. The region-of-interest (ROI) values obtained in reconstructed images without scatter
and attenuation corrections were used to calculate the CCFs of the PET scanner. and attenuation corrections were used to calculate the CCFs of the PET scanner.
ResultsThe CCFs obtained by the proposed method agreed with those obtained by the standard cross-calibration (CC) method within a ResultsThe CCFs obtained by the proposed method agreed with those obtained by the standard cross-calibration (CC) method within a
precision of 1.5% (σ). The temporal variations in the CCFs by the standard CC method were reproduced by the proposed method precision of 1.5% (σ). The temporal variations in the CCFs by the standard CC method were reproduced by the proposed method
with a precision better than 1%. with a precision better than 1%.
ConclusionThe CC method with a moving 22Na point-like radioactive source is practically useful for determining the CCFs of PET scanners and monitoring their variations. ConclusionThe CC method with a moving 22Na point-like radioactive source is practically useful for determining the CCFs of PET scanners and monitoring their variations.
KeywordsPET-Calibration-Point-like source- KeywordsPET-Calibration-Point-like source-
22Na-Traceability 22Na-Traceability
Annals of Nuclear Medicine 04/2012; 24(9):655-661. · 1.50 Impact Factor
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ABSTRACT: We have proposed an OpenPET geometry which consists of two axially separated detector rings. The open gap is suitable for in-beam PET. We have developed the small prototype of the OpenPET especially for a proof of concept of in-beam imaging. This paper presents an overview of the main features implemented in this prototype. We also evaluated the detector performance. This prototype was designed with 2 detector rings having 8 depth-of-interaction detectors. Each detector consisted of 784 Lu(2x)Gd(2(1-x))SiO₅:Ce (LGSO) which were arranged in a 4-layer design, coupled to a position-sensitive photomultiplier tube (PS-PMT). The size of the LGSO array was smaller than the sensitive area of the PS-PMT, so that we could obtain sufficient LGSO identification. Peripheral LGSOs near the open gap directly detect the gamma rays on the side face in the OpenPET geometry. Output signals of two detectors stacked axially were projected onto one 2-dimensional position histogram for reduction of the scale of a coincidence processor. Front-end circuits were separated from the detector head by 1.2-m coaxial cables for the protection of electronic circuits from radiation damage. The detectors had sufficient crystal identification capability. Cross talk between the combined two detectors could be ignored. The timing and energy resolutions were 3.0 ns and 14%, respectively. The coincidence window was set 20 ns, because the timing histogram showed that not only the main peak, but also two small shifted peaks were caused by the coaxial cable. However, the detector offers the promise of sufficient performance, because random coincidences are at a nearly undetectable level for in-beam PET experiments.
Radiological Physics and Technology 11/2011; 5(1):92-7.
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ABSTRACT: We are developing a novel, general purpose isotropic-3D PET detector X'tal cube which has high spatial resolution in all three dimensions. The research challenge for this detector is implementing effective detection of scintillation photons by covering six faces of a segmented crystal block with silicon photomultipliers (SiPMs). In this paper, we developed the second prototype of the X'tal cube for a proof-of-concept. We aimed at realizing an ultimate detector with 1.0 mm(3) cubic crystals, in contrast to our previous development using 3.0 mm(3) cubic crystals. The crystal block was composed of a 16 × 16 × 16 array of lutetium gadolinium oxyorthosilicate (LGSO) crystals 0.993 × 0.993 × 0.993 mm(3) in size. The crystals were optically glued together without inserting any reflector inside and 96 multi-pixel photon counters (MPPCs, S10931-50P, i.e. six faces each with a 4 × 4 array of MPPCs), each having a sensitive area of 3.0 × 3.0 mm(2), were optically coupled to the surfaces of the crystal block. Almost all 4096 crystals were identified through Anger-type calculation due to the finely adjusted reflector sheets inserted between the crystal block and light guides. The reflector sheets, which formed a belt of 0.5 mm width, were placed to cover half of the crystals of the second rows from the edges in order to improve identification performance of the crystals near the edges. Energy resolution of 12.7% was obtained at 511 keV with almost uniform light output for all crystal segments thanks to the effective detection of the scintillation photons.
Physics in Medicine and Biology 11/2011; 56(21):6793-807. · 2.83 Impact Factor
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ABSTRACT: The uncertainty of radioactivity concentrations measured with positron emission tomography (PET) scanners ultimately depends on the uncertainty of the calibration factors. A new practical calibration scheme using point-like (22)Na radioactive sources has been developed. The purpose of this study is to theoretically investigate the effects of the associated 1.275 MeV γ rays on the calibration factors. The physical processes affecting the coincidence data were categorized in order to derive approximate semi-quantitative formulae. Assuming the design parameters of some typical commercial PET scanners, the effects of the γ rays as relative deviations in the calibration factors were evaluated by semi-quantitative formulae and a Monte Carlo simulation. The relative deviations in the calibration factors were less than 4%, depending on the details of the PET scanners. The event losses due to rejecting multiple coincidence events of scattered γ rays had the strongest effect. The results from the semi-quantitative formulae and the Monte Carlo simulation were consistent and were useful in understanding the underlying mechanisms. The deviations are considered small enough to correct on the basis of precise Monte Carlo simulation. This study thus offers an important theoretical basis for the validity of the calibration method using point-like (22)Na radioactive sources.
Physics in Medicine and Biology 08/2011; 56(18):6031-45. · 2.83 Impact Factor
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Taiga Yamaya,
Eiji Yoshida,
Taku Inaniwa,
Shinji Sato,
Yasunori Nakajima,
Hidekatsu Wakizaka,
Daisuke Kokuryo,
Atsushi Tsuji,
Takayuki Mitsuhashi,
Hideyuki Kawai,
Hideaki Tashima,
Fumihiko Nishikido,
Naoko Inadama, Hideo Murayama,
Hideaki Haneishi,
Mikio Suga,
Shoko Kinouchi
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ABSTRACT: The OpenPET geometry is our new idea to visualize a physically opened space between two detector rings. In this paper, we developed the first small prototype to show a proof-of-concept of OpenPET imaging. Two detector rings of 110 mm diameter and 42 mm axial length were placed with a gap of 42 mm. The basic imaging performance was confirmed through phantom studies; the open imaging was realized at the cost of slight loss of axial resolution and 24% loss of sensitivity. For a proof-of-concept of PET image-guided radiation therapy, we carried out the in-beam tests with (11)C radioactive beam irradiation in the heavy ion medical accelerator in Chiba to visualize in situ distribution of primary particles stopped in a phantom. We showed that PET images corresponding to dose distribution were obtained. For an initial proof-of-concept of real-time multimodal imaging, we measured a tumor-inoculated mouse with (18)F-FDG, and an optical image of the mouse body surface was taken during the PET measurement by inserting a digital camera in the ring gap. We confirmed that the tumor in the gap was clearly visualized. The result also showed the extension effect of an axial field-of-view (FOV); a large axial FOV of 126 mm was obtained with the detectors that originally covered only an 84 mm axial FOV. In conclusion, our initial imaging studies showed promising performance of the OpenPET.
Physics in Medicine and Biology 02/2011; 56(4):1123-37. · 2.83 Impact Factor
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ABSTRACT: Conventionally, block detectors, which consist of a two-dimensionally segmented scintillator array with inserted reflectors, are often used for PET. On the other hand, PET detectors with a monolithic block have been investigated because they are expected to offer higher resolution than do segmented crystal arrays. However, previous reports focused on detectors dedicated as small-animal PET, and the thickness was not good enough to stop 511-keV radiation. We developed a PET detector that uses a large and thick monolithic LYSO and 64-channel PS-PMT. When the LYSO was covered with reflectors, the spatial resolution, which was 3 mm FWHM at the center, rapidly became worse at the edge. We eliminated the loss of spatial resolution by replacing the reflectors with black paper, but the light output was decreased. Therefore, we concluded that spatial resolution and light output were in a trade-off relationship due to the edge effect of scintillation light.
Radiological Physics and Technology 02/2011; 4(2):134-9.
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ABSTRACT: Thus far, cylindrical phantoms with (18)F or (68)Ge/(68)Ga have been used in the standard techniques for determining the cross-calibration factors (CCFs) of PET scanners. This paper describes a new practical method that uses a point-like (22)Na radioactive source for determining CCFs.
A point-like (22)Na radioactive source (about 700 kBq) was equipped with a spherical aluminium absorber capsule to ensure the symmetry of the emitted photons. During measurements, the source was moved in the axial direction to cover the whole axial field of view (FOV) of a clinical PET scanner, SET-2400 W. The region-of-interest (ROI) values obtained in reconstructed images without scatter and attenuation corrections were used to calculate the CCFs of the PET scanner.
The CCFs obtained by the proposed method agreed with those obtained by the standard cross-calibration (CC) method within a precision of 1.5% (σ). The temporal variations in the CCFs by the standard CC method were reproduced by the proposed method with a precision better than 1%.
The CC method with a moving (22)Na point-like radioactive source is practically useful for determining the CCFs of PET scanners and monitoring their variations.
Annals of Nuclear Medicine 11/2010; 24(9):655-61. · 1.50 Impact Factor
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ABSTRACT: Radioactive sources for evaluating sensitivity and uncertainty in the radioactivity measurements performed using PET scanners must be equipped with absorber materials that ensure the annihilation of positrons. Attenuation and scattering owing to the absorber materials produce uncertainty in the performance evaluation. The aim of this study is to propose a point-like radioactive source with multiple absorber capsules, for which evaluation can be independent of scatter and attenuation owing to the source absorbers.
The point-like source consists of a small spherical radioactive part and a set of successively sized cylindrical aluminum absorber capsules. Data were collected for different total absorber thicknesses. By an extrapolation technique, the effects of the source absorbers were eliminated. Sensitivity and uncertainty in the radioactivity measurements of PET scanners were evaluated with this technique.
Sensitivity and uncertainty of radioactivity measurement to the point-like radioactive source were evaluated successfully with this method.
The proposed point-like radioactive source is useful for evaluating performance characteristics of PET scanners in a way that is independent of the effects of the source absorbers.
Annals of Nuclear Medicine 02/2010; 24(5):427-32. · 1.50 Impact Factor
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Tomoyuki Hasegawa,
Haruna Kojima,
Chisato Masu,
Yasuhiro Fukushima,
Hironori Kojima,
Kiminori Konokawa,
Tomonori Isobe,
Eisuke Sato, Hideo Murayama,
Koichi Maruyama,
Tokuo Umeda
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ABSTRACT: Physics-related subjects are important in the educational fields of radiological physics and technology. However, conventional teaching tools, for example texts, equations, and two-dimensional figures, are not very effective in attracting the interest of students. Therefore, we have created several multimedia educational materials covering radiological physics and technology. Each educational presentation includes several segments of high-quality computer-graphic animations designed to attract students' interest. We used personal computers (PCs) and commercial software to create and compile these. Undergraduate and graduate students and teachers and related professionals contributed to the design and creation of the educational materials as part of student research. The educational materials can be displayed on a PC monitor and manipulated with popular free software. Opinion surveys conducted in undergraduate courses at Kitasato University support the effectiveness of our educational tools in helping students gain a better understanding of the subjects offered and in raising their interest.
Radiological Physics and Technology 01/2010; 3(1):1-9.
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ABSTRACT: We are currently developing an imaging system that combines simultaneous positron emission tomography (PET) with near-infrared (NIR) optical tomography, thus supporting two different types of molecular imaging. For this system, we are considering whether to use depth of interaction (DOI) PET detectors as simultaneous detectors of gamma rays and NIR light by changing the original upper reflectors to dichroic mirrors. The DOI-PET detector has very low spatial resolution for NIR light compared to the charge-coupled device cameras that are normally used. However, it is possible to reconstruct images of comparable value from the data acquired by low-resolution devices because the light is scattered by biological tissues and high-resolution devices are not necessarily effective at improving image quality. In this study, we demonstrate the feasibility of 3D NIR fluorescence tomography imaging by employing DOI-PET detectors in computer simulations. In the simulations, we used a 40 mm x 40 mm x 40 mm cubic phantom, a square detector geometry, and an optical diffusion equation to approximate the light propagation. We then evaluated imaging systems for 3D fluorescence tomography with different detector resolutions and excitation light arrangements using singular-value analysis and imaging simulation. We confirmed that the reconstructed images from low-resolution detectors (8 x 8 pixels for an area of 40 mm x 40 mm) are the same as those from high-resolution detectors (16 x 16 pixels for the same area).
Radiological Physics and Technology 07/2009; 2(2):189-97.
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ABSTRACT: One trend in positron emission tomography (PET) instrumentation over the last decade has been the development of scanners dedicated to small animals such as rats and mice. Thicker crystals, which are necessary to obtain higher sensitivity, result in degraded spatial resolution in the peripheral field-of-view (FOV) owing to the parallax error. On the other hand, we are developing the jPET-D4, which is a dedicated human brain PET scanner that has a capability for depth-of-interaction (DOI) measurement. Although its crystal width is about twice that of commercially available small animal PET scanners, we expect the jPET-D4 to have a potential for small animal imaging by making full use of the DOI information. In this article, we investigate the jPET-D4's potential for small animal imaging by comparing it with the microPET Focus220, a state-of-the-art PET scanner dedicated to small animals.
The jPET-D4 uses four-layered GSO crystals measuring 2.9 mm x 2.9 mm x 7.5 mm, whereas the microPET Focus220 uses a single layer of LSO crystals measuring 1.5 mm x 1.5 mm x 10.0 mm. First, the absolute sensitivity, counting rate performance and spatial resolution of both scanners were measured. Next a small hot-rod phantom was used to compare their imaging performance. Finally, a rat model with breast tumors was imaged using the jPET-D4.
Thanks to the thicker crystals and the longer axial FOV, the jPET-D4 had more than four times higher sensitivity than the microPET Focus220. The noise equivalent counting-rate performance of the jPETD4 reached 1,024 kcps for a rat-size phantom, whereas that of the microPET Focus220 reached only 165 kcps. At the center of the FOV, the resolution was 1.7 mm for the microPET Focus220, whereas it was 3.2 mm for the jPET-D4. On the other hand, the difference of resolution became smaller at the off-center position because the radial resolution degraded faster for the microPET Focus220. The results of phantom imaging showed that the jPET-D4 was comparable to the microPET Focus220 at the off-center position even as the microPET Focus220 outperformed the jPET-D4 except for the peripheral FOV.
The jPET-D4 human brain PET scanner, which was designed to achieve not only high resolution but also high sensitivity by measuring DOI information, was proven to have a potential for small animal imaging.
Annals of Nuclear Medicine 03/2009; 23(2):183-90. · 1.50 Impact Factor
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ABSTRACT: The energy loss distribution of beta+ particles is closely related to their maximum penetration depth distribution and annihilation point distribution. The latter is of practical importance for positron emission tomography. Experimental data related to the energy loss distribution are important for comprehensive validation of physics and simulation models of beta+ interactions. In this paper the authors present a new experimental approach that allows them to visually observe the beta+ energy loss distribution of a solution of nuclear medicine radioisotopes in a plastic scintillator using an optical camera. The authors also report a set of the first experimental results. A water solution of 18F was localized in a small hole in a plastic scintillator (BC430). Optical imaging of the scintillator yielded visual images of the energy loss distribution with a submillimeter resolution. The radial dependence in the energy distribution was quantitatively measured by analysis of the images, and exponential fitting parameters were obtained. The authors observed that the results of Monte Carlo simulation with EGS5 (version 1.0.2) and GEANT4 (version 4.9.01.p01) were consistent with those obtained experimentally. The results of the Monte Carlo simulation indicated that for a linear scale, the energy loss distribution in the scintillator was approximately the same as that in water, and the relative shape of the energy loss distribution was close to those of the maximum penetration depth distribution and annihilation point distribution. This paper also presents discussions about the further possibilities of this optical imaging approach. Thus, optical observation of the beta+ energy loss distribution in a scintillator is a promising technique for visual and quantitative experimental studies of beta+ emission from a solution of radioisotopes that are used in nuclear medicine.
Medical Physics 03/2009; 36(2):402-10. · 2.83 Impact Factor
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ABSTRACT: We have proposed an 'OpenPET' geometry which consists of two detector rings of axial length W each axially separated by a gap G. In order to obtain an axially continuous field-of-view (FOV) of 2W+G, the maximum limit for G must be W. However, two valleys of sensitivity appear, one on each side of the gap. In practice, the gap should be G<W in order to compensate for the sensitivity valleys. In this paper, we proposed an alternative method to improve uniformity of the sensitivity while maintaining the gap. The proposed geometry consisted of four units of detector rings obtained by dividing each right and left unit of detector rings into two units. The inner two units formed the main gap, and the outer two units were appropriately placed to improve the uniformity of sensitivity. The geometry was optimized to minimize the standard deviation of the sensitivity distribution. Numerical simulation results supported the effectiveness of the proposed method. The outer units compensated for the sensitivity valleys on both sides of the main gap. A more appropriate geometry should be designed for the desired application, such as a long axial FOV PET and in-beam PET.
Physics in Medicine and Biology 01/2009; 54(5):1223-33. · 2.83 Impact Factor
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ABSTRACT: We have proposed a new "OpenPET" geometry consisting of two detector rings of axial length W each separated by a gap G. For obtaining an axially continuous field of view (FOV) of 2W + G, the maximum limit for G must be W. However, two valleys of sensitivity appear on both sides of the gap. Setting a more limited range for the gap as G < W, which is desirable for filling in the sensitivity valleys, results in not only a shortened gap, but also a shortened axial FOV. In this paper, we propose an alternative method for improving the uniformity of sensitivity by shifting two detector rings axially closer or further apart at the same velocity to each other. In addition, image reconstruction of the OpenPET is an incomplete problem, and low-frequency components are missing in the gap. Therefore, the proposed method is also expected to improve the conditions for the inverse problem. We simulated an OpenPET scanner which measures events simultaneously by shifting the detector rings. The results showed that the right and left peaks of the sensitivity approach each other upon shifting of the detector rings, and these valleys of sensitivity are effectively recovered. The results also showed that distortion, which is observed for objects containing low-frequency components, is reduced. Larger detector shifts allow a more uniform axial distribution of sensitivity and a higher image quality, but at the cost of a smaller minimum gap. Therefore, an appropriate detector-shifting pattern should be determined based on the desired scanner application.
Radiological Physics and Technology 01/2009; 2(1):62-9.
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ABSTRACT: For depth of interaction (DOI) encoding on a PET detector, we propose to use scintillation crystals, each cut as a triangular prism. Demonstration of the method for the 3-layer and 2-layer DOI encodings was carried out with two shapes of Lu 2x Gd 2(1−x) SiO 5 (LGSO) crystals: an equilateral triangle of 3.0 mm length per side and a isosceles right triangle of 3.0 mm length for two sides in their horizontal cross section. The height of each crystal prism was 10.0 mm. The former and latter crystal shapes were arranged in 3-layer and 2-layer DOI array, respectively, and their performances were evaluated by coupling the array to a position sensitive photomultiplier tube (PS-PMT). By Anger-type calculations of the PS-PMT signals, we obtained 2-dimensional position histograms in which responses of the crystals in all layers were represented. Both DOI detectors showed promising results for crystal identification and energy performances.
Nuclear Science Symposium Conference Record, 2008. NSS '08. IEEE; 11/2008
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ABSTRACT: Silicon photomultipliers are promising photo detectors for use in PET detectors due to their high internal gain, low power consumption and insensitivity to magnetic fields. We are developing a PET detector which consists of a scintillation crystal array and a silicon photomultiplier array. To achieve uniform spatial resolution, depth-of-interaction (DOI) detectors are required to reduce the parallax error. In this paper, we are studying the four-layer DOI PET detector with a silicon photomultiplier array.
Nuclear Science Symposium Conference Record, 2008. NSS '08. IEEE; 11/2008
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ABSTRACT: The long patient port of a PET scanner tends to put stress on patients, especially patients with claustrophobia. It also prevents doctors and technicians from taking care of patients during scanning. In this paper, we proposed an 'open PET' geometry, which consists of two axially separated detector rings. A long and continuous field-of-view (FOV) including a 360 degrees opened gap between two detector rings can be imaged enabling a fully 3D image reconstruction of all the possible lines-of-response. The open PET will become practical if iterative image reconstruction methods are applied even though image reconstruction of the open PET is analytically an incomplete problem. First we implemented a 'masked' 3D ordered subset expectation maximization (OS-EM) in which the system matrix was obtained from a long 'gapless' scanner by applying a mask to detectors corresponding to the open space. Next, in order to evaluate imaging performance of the proposed open PET geometry, we simulated a dual HR+ scanner (ring diameter of D = 827 mm, axial length of W = 154 mm x 2) separated by a variable gap. The gap W was the maximum limit to have axially continuous FOV of 3W though the maximum diameter of FOV at the central slice was limited to D/2. Artifacts, observed on both sides of the open space when the gap exceeded W, were effectively reduced by inserting detectors partially into unnecessary open spaces. We also tested the open PET geometry using experimental data obtained by the jPET-D4. The jPET-D4 is a prototype brain scanner, which has 5 rings of 24 detector blocks. We simulated the open jPET-D4 with a gap of 66 mm by eliminating 1 block-ring from experimental data. Although some artifacts were seen at both ends of the opened gap, very similar images were obtained with and without the gap. The proposed open PET geometry is expected to lead to realization of in-beam PET, which is a method for an in situ monitoring of charged particle therapy, by letting the beams pass through the gap. The proposed open PET geometry will also allow simultaneous PET/CT measurements of the same PET FOV as the CT FOV, in contrast to the conventional PET/CT where each FOV is separated by several tens of centimeters.
Physics in Medicine and Biology 03/2008; 53(3):757-73. · 2.83 Impact Factor
