The Experts below are selected from a list of 43647 Experts worldwide ranked by ideXlab platform
Freek J Beekman - One of the best experts on this subject based on the ideXlab platform.
-
absolute quantitative total body small animal spect with focusing Pinholes
European Journal of Nuclear Medicine and Molecular Imaging, 2010Co-Authors: Chao Wu, Frans Van Der Have, Brendan Vastenhouw, Rudi Dierckx, A M J Paans, Freek J BeekmanAbstract:Purpose In Pinhole SPECT, attenuation of the photon flux on trajectories between source and Pinholes affects quantitative accuracy of reconstructed images. Previously we introduced iterative methods that compensate for image degrading effects of detector and Pinhole blurring, Pinhole sensitivity and scatter for multi-Pinhole SPECT. The aim of this paper is (1) to investigate the accuracy of the Chang algorithm in rodents and (2) to present a practical Chang-based method using body outline contours obtained with optical cameras.
-
optimizing multi Pinhole spect geometries using an analytical model
Physics in Medicine and Biology, 2007Co-Authors: M.c.m. Rentmeester, Frans Van Der Have, Freek J BeekmanAbstract:State-of-the-art multi-Pinhole SPECT devices allow for sub-mm resolution imaging of radio-molecule distributions in small laboratory animals. The optimization of multi-Pinhole and detector geometries using simulations based on ray-tracing or Monte Carlo algorithms is time-consuming, particularly because many system parameters need to be varied. As an efficient alternative we develop a continuous analytical model of a Pinhole SPECT system with a stationary detector set-up, which we apply to focused imaging of a mouse. The model assumes that the multi-Pinhole collimator and the detector both have the shape of a spherical layer, and uses analytical expressions for effective Pinhole diameters, sensitivity and spatial resolution. For fixed fields-of-view, a Pinhole-diameter adapting feedback loop allows for the comparison of the system resolution of different systems at equal system sensitivity, and vice versa. The model predicts that (i) for optimal resolution or sensitivity the collimator layer with Pinholes should be placed as closely as possible around the animal given a fixed detector layer, (ii) with high-resolution detectors a resolution improvement up to 31% can be achieved compared to optimized systems, (iii) high-resolution detectors can be placed close to the collimator without significant resolution losses, (iv) interestingly, systems with a physical Pinhole diameter of 0 mm can have an excellent resolution when high-resolution detectors are used.
-
the Pinhole gateway to ultra high resolution three dimensional radionuclide imaging
European Journal of Nuclear Medicine and Molecular Imaging, 2007Co-Authors: Freek J Beekman, Frans Van Der HaveAbstract:Today the majority of clinical molecular imaging procedures are carried out with single-photon emitters and gamma cameras, in planar mode and single-photon emission computed tomography (SPECT) mode. Thanks to the development of advanced multi-Pinhole collimation technologies, SPECT imaging of small experimental animals is rapidly gaining in popularity. Whereas resolutions in routine clinical SPECT are typically larger than 1 cm (corresponding to >1,000 μl), it has recently proved possible to obtain spatial resolutions of about 0.35 mm (≈0.04 μl) in the mouse. Meanwhile, SPECT systems that promise an even better performance are under construction. The new systems are able to monitor functions in even smaller structures of the mouse than was possible with dedicated small animal positron emission tomography (≈1 mm resolution, corresponding to 1 μl). This paper provides a brief history of image formation with Pinholes and explains the principles of Pinhole imaging and Pinhole tomography and the basics of modern image reconstruction methods required for such systems. Some recently introduced ultra-high-resolution small animal SPECT instruments are discussed and new avenues for improving system performance are explored. This may lead to many completely new biomedical applications. We also demonstrate that clinical SPECT systems with focussing Pinhole gamma cameras will be able to produce images with a resolution that may become superior to that of PET for major clinical applications. A design study of a cardiac Pinhole SPECT system indicates that the heart can be imaged an order of magnitude faster or with much more detail than is possible with currently used parallel-hole SPECT (e.g. 3–4 mm instead of ≈8 mm system resolution).
-
penetration scatter and sensitivity in channel micro Pinholes for spect a monte carlo investigation
IEEE Transactions on Nuclear Science, 2006Co-Authors: Frans Van Der Have, Freek J BeekmanAbstract:Channel-edge Pinhole designs have been proposed in order to reduce the penetration of gamma rays through the edge of the Pinhole aperture. A characterization of penetration and scatter in the Pinhole aperture metal can be used in the design of small animal SPECT collimators or for model based corrections during micro-SPECT image reconstruction. In this study the penetration and scatter contributions of micro-Pinholes were compared for Tc-99m, I-123, and I-125 for knife-edges and channel-edges. To this end, Geant 4 Monte Carlo simulations of 0.3 mm and 0.5 mm diameter apertures with acceptance angles ranging from 20 to 60 degrees were performed. At perpendicular incidence of the photons, channel Pinholes had lower penetration and scatter fractions than did knife-edge Pinholes. This advantage disappeared at higher angles of incidence. In addition, the total sensitivity decreased substantially with increasing channel height. Planar projection images of a grid of spheres showed that channel-edge Pinholes resulted in a slightly higher spatial resolution than knife-edge Pinholes with an equal diameter, when combined with a high-resolution detector. However, the channel-edge Pinhole's sensitivity and Contrast Inverse Coefficient of Variation were lower than the knife edge Pinhole's at the edges of the detector. We conclude that channel Pinholes can result in lower imaging performance when used with non-perpendicular incidence photons because of loss of sensitivity
-
Continuous model of multi-Pinhole SPECT devices
IEEE Nuclear Science Symposium Conference Record 2005, 2005Co-Authors: M.c.m. Rentmeester, Frans Van Der Have, Freek J BeekmanAbstract:Recently multi-Pinhole SPECT systems have been proposed that allow for sub-mm resolution imaging in mice. The optimization of multi-Pinhole systems using ray-tracing or Monte Carlo simulation is extremely time consuming. As an alternative we develop an approximate continuous model of a SPECT system which we apply to focused Pinhole imaging of the mouse. In order to facilitate the use of analytical mathematical calculations the model assumes that the system consists of spherical layers. It uses analytical expressions of effective Pinhole diameters, sensitivity, and resolution. With a Pinhole-diameter adapting feedback loop that allows to compare system resolution at equal system sensitivity and vice versa the model predicts that (i) for optimal resolution Pinholes should be as close as possible to the animal, (ii) with high resolution (
Roel Van Holen - One of the best experts on this subject based on the ideXlab platform.
-
The Evaluation of Data Completeness and Image Quality in Multiplexing Multi-Pinhole SPECT
IEEE Transactions on Medical Imaging, 2015Co-Authors: Karen Van Audenhaege, Stefaan Vandenberghe, Christian Vanhove, Roel Van HolenAbstract:Multi-Pinhole collimators are often used in pre-clinical SPECT systems because they have a better resolution-sensitivity tradeoff than parallel hole collimators when imaging small objects. Most multi-Pinhole collimators are designed to allow no or only a limited amount of overlap between the different Pinhole projections because the ambiguity introduced by multiplexing Pinholes can result in artifacts. The origin of these artifacts is still not fully understood, but previous research has already shown that data incompleteness could be part of the explanation. Therefore, we developed a method to investigate data completeness in multiplexing multi-Pinhole systems and showed that a certain activity distribution can be successfully reconstructed when the nonmultiplexed data is complete or when the overlap can be sufficiently de-multiplexed. We validated this method using computer simulated phantom data of different multiplexing systems. We also studied contrast-to-noise and nonprewhitening matched filter signal-to-noise ratio (NPW-SNR) to compare the image quality in a single Pinhole system with multiplexing systems. We found that our method can indeed be used to evaluate data completeness in multiplexing systems and found no artifacts in the systems that had complete data. Sensitivity increased significantly with multiplexing but we found only small, nonsignificant differences in contrast-to-noise ratio. However, the NPW-SNR did slightly improve in the multiplexing setups. We conclude that more multiplexing does not necessarily result in more artifacts and that even a high amount of multiplexing can still result in artifact-free images if the nonmultiplexed data is complete or when the overlap can be sufficiently de-multiplexed.
-
Data completeness in multiplexing multi-Pinhole SPECT
2013 IEEE Nuclear Science Symposium and Medical Imaging Conference (2013 NSS MIC), 2013Co-Authors: Karen Van Audenhaege, Stefaan Vandenberghe, Christian Vanhove, Roel Van HolenAbstract:Multi-Pinhole collimators are often used in preclinical SPECT systems because of their high resolution and reasonable sensitivity. Most multi-Pinhole collimators are designed to allow only a limited amount of overlap between the different Pinholes' projections (also called multiplexing) because it has been shown that the ambiguity introduced by multiplexing Pinholes can result in artifacts.
-
characterization of a spect Pinhole collimator for optimal detector usage the lofthole
Physics in Medicine and Biology, 2013Co-Authors: Karel Deprez, Stefaan Vandenberghe, Lara Da Rocha Vaz Pato, Roel Van HolenAbstract:In single-photon emission computed tomography (SPECT), multi-Pinhole collimation is often employed nowadays. Most multi-Pinhole collimators avoid overlap (multiplexing) of the projections on the detector. This can be done by using additional shielding or by spacing the Pinholes far enough apart. Using additional shielding has the drawback that it increases weight, design complexity and cost. Spacing the Pinholes far enough apart results in sub-optimal detector usage, the valuable detector area is not entirely used. This is due to the circular projections of Pinholes on the detector; these ellipses can not be tiled with high detector coverage. To overcome this we designed a new Pinhole geometry, the lofthole, that has a rectangular projection on the detector. The lofthole has a circular aperture and a rectangular entrance/exit opening. Sensitivity formulae have been derived for Pinholes and loftholes. These formulae take the penumbra effect into account; the proposed formulae do not take penetration into account. The derived formulae are valid for geometries where the field-of-view and the sensitivity of the aperture are solely limited by the exit window. A flood map measurement was performed to compare the rectangular projection of a lofthole with the circular projection of a Pinhole. Finally, measurements were done to compare the amount of penetration of Pinholes with the amount of penetration of a lofthole. A square lofthole collimator has less penetration than a knife-edge Pinhole collimator that irradiates the same rectangular detector area with full coverage. A multi-lofthole collimator allows high detector coverage without using additional shielding. An additional advantage is the lower amount of penetration.
-
The lofthole: A novel shaped Pinhole geometry for optimal detector usage without multiplexing and without additional shielding
2011 IEEE Nuclear Science Symposium Conference Record, 2011Co-Authors: Karel Deprez, Roel Van Holen, Stefaan VandenbergheAbstract:Multi-Pinhole collimator based SPECT systems are nowadays used for pre-clinical and clinical imaging. Overlap of the different projections of the Pinholes should generally be avoided. This can be done by either positioning the Pinholes far from each other or by using additional shielding. The first method does not allow to use the detector area efficiently while the second method introduces additional cost, weight and design complexity. We investigate a new Pinhole geometry, the lofthole, that has a circular aperture but whose entrance and/or exit opening is shaped by the desired irradiated detector area. The lofthole is designed using a ray-tracer and can be manufactured with traditional manufacturing techniques. A lofthole and two regular Pinholes have been made in two tungsten-alloy plates. Production of these plates indicates that the manufacturing cost of a Pinhole is roughly similar to the manufacturing cost of a lofthole. Measurements on the lofthole and Pinhole plates show the rectangular projection of the lofthole versus the circular projection of the Pinhole. Penetration measurements indicate that the lofthole has less penetration than a Pinhole that irradiates the same detector area.
Felix N Buchi - One of the best experts on this subject based on the ideXlab platform.
-
factors determining the gas crossover through Pinholes in polymer electrolyte fuel cell membranes
Electrochimica Acta, 2012Co-Authors: Stefan Kreitmeier, Matteo Michiardi, Alexander Wokaun, Felix N BuchiAbstract:Abstract Membrane degradation in polymer electrolyte fuel cells often results in Pinhole formation, which does not force an immediate fuel cell shutdown, as the performance is still good and the gas crossover is moderate for low membrane defect densities. However, the gas crossover increases locally at defects, which may accelerate chemical polymer decomposition and enlarge the defect. Hence, a fundamental understanding of the gas crossover through small Pinholes is required to deduce strategies mitigating fast membrane degradation. Methods are developed to implement Pinholes (10 μm) artificially in polymer electrolyte membranes. The Pinhole morphology and chemical environment are characterized by X-ray tomographic microscopy and FTIR spectro-microscopy. The gas crossover is measured in situ for different fuel cell operating conditions using a mass spectrometry based method. In saturated environment liquid water can seal Pinholes and eliminate the crossover. This sealing effect depends on the Pinhole size and the pressure gradient between anode and cathode. Increasing temperature or humidity reduces the gas crossover. Hydrogen, permeating through defects, does not oxidize quantitatively at the cathode catalyst layer, but permeates through the gas diffusion layer (GDL) into the gas channel. Then, the permeability of the GDL, in particular its micro-porous layer, limits the gas crossover through Pinholes significantly.
-
Factors determining the gas crossover through Pinholes in polymer electrolyte fuel cell membranes
Electrochimica Acta, 2012Co-Authors: Stefan Kreitmeier, Matteo Michiardi, Alexander Wokaun, Felix N BuchiAbstract:Membrane degradation in polymer electrolyte fuel cells often results in Pinhole formation, which does not force an immediate fuel cell shutdown, as the performance is still good and the gas crossover is moderate for low membrane defect densities. However, the gas crossover increases locally at defects, which may accelerate chemical polymer decomposition and enlarge the defect. Hence, a fundamental understanding of the gas crossover through small Pinholes is required to deduce strategies mitigating fast membrane degradation. Methods are developed to implement Pinholes (10 μm) artificially in polymer electrolyte membranes. The Pinhole morphology and chemical environment are characterized by X-ray tomographic microscopy and FTIR spectro-microscopy. The gas crossover is measured in situ for different fuel cell operating conditions using a mass spectrometry based method. In saturated environment liquid water can seal Pinholes and eliminate the crossover. This sealing effect depends on the Pinhole size and the pressure gradient between anode and cathode. Increasing temperature or humidity reduces the gas crossover. Hydrogen, permeating through defects, does not oxidize quantitatively at the cathode catalyst layer, but permeates through the gas diffusion layer (GDL) into the gas channel. Then, the permeability of the GDL, in particular its micro-porous layer, limits the gas crossover through Pinholes significantly. © 2012 Elsevier Ltd.
Paul D Acton - One of the best experts on this subject based on the ideXlab platform.
-
Simulation of a Pinhole-collimator insert for small animal PET using GATE
2007 IEEE Nuclear Science Symposium Conference Record, 2007Co-Authors: Christopher Cardi, Paul D Acton, Mathew L. ThakurAbstract:In previous work we demonstrated the feasibility to conduct SPECT imaging using a multi-Pinhole collimator insert in a small animal PET scanner. A simplified analytical simulation method was used, modeling mainly geometric attributes, to optimize the multi-Pinhole configuration to achieve the best trade-off between resolution and sensitivity for specific applications. To more accurately optimize the Pinhole configuration more physical attributes need to be modeled, including attenuation and scatter in both the object and collimator. In this work we used GATE, a Monte Carlo simulation platform based on the well-validated Geant4 libraries, to better model our system. New simulations have been performed using the geometry of the MOSAIC (Philips) system and our simple prototype cylindrical insert (lead, 12 Pinholes, Pinhole diameter 1.0 mm, insert diameter 60 mm). Measurements of sensitivity (0.22%), resolution (FWHM=1.6 mm), and scatter fraction (28%) using point and capillary sources from GATE-simulated data are in good agreement with measured experimental data. Having validated this simulation environment with this baseline test, we are iteratively testing various objects, Pinhole configurations, and collimator materials to design our next generation of optimal Pinhole configurations for specific imaging tasks.
-
optimal number of Pinholes in multi Pinhole spect for mouse brain imaging a simulation study
Physics in Medicine and Biology, 2005Co-Authors: Riccardo Accorsi, Paul D ActonAbstract:This study simulates a multi-Pinhole single-photon emission computed tomography (SPECT) system using the Monte Carlo method, and investigates different multi-Pinhole designs for quantitative mouse brain imaging. Prior approaches investigating multi-Pinhole SPECT were not often optimal, as the number and geometrical arrangement of Pinholes were usually chosen empirically. The present study seeks to optimize the number of Pinholes for a given Pinhole arrangement, and also for the specific application of quantitative neuroreceptor binding in the mouse brain. An analytical Monte Carlo simulation based method was used to generate the projection data for various count levels. A three-dimensional ordered-subsets expectation-maximization algorithm was developed and used to reconstruct the images, incorporating a realistic Pinhole model for resolution recovery and noise reduction. Although artefacts arising from overlapping projections could be a major problem in multi-Pinhole reconstruction, the cold-rod phantom study showed minimal loss of spatial resolution in multi-Pinhole systems, compared to a single-Pinhole system with the same Pinhole diameter. A quantitative study of neuroreceptor binding sites using a mouse brain phantom and low activity (37 MBq) showed that the multi-Pinhole system outperformed the single-Pinhole system by maintaining the mean and lowering the variance in the measured uptake ratio. Multi-Pinhole collimation can be used to reduce the injected dose and thereby reduce the radiation exposure to the animal. Results also suggest that the nine-Pinhole configuration shown in this paper is a good choice for mouse brain imaging.
-
Optimal number of Pinholes in multi-Pinhole SPECT for mouse brain imaging—a simulation study
Physics in Medicine and Biology, 2005Co-Authors: Riccardo Accorsi, Paul D ActonAbstract:This study simulates a multi-Pinhole single-photon emission computed tomography (SPECT) system using the Monte Carlo method, and investigates different multi-Pinhole designs for quantitative mouse brain imaging. Prior approaches investigating multi-Pinhole SPECT were not often optimal, as the number and geometrical arrangement of Pinholes were usually chosen empirically. The present study seeks to optimize the number of Pinholes for a given Pinhole arrangement, and also for the specific application of quantitative neuroreceptor binding in the mouse brain. An analytical Monte Carlo simulation based method was used to generate the projection data for various count levels. A three-dimensional ordered-subsets expectation-maximization algorithm was developed and used to reconstruct the images, incorporating a realistic Pinhole model for resolution recovery and noise reduction. Although artefacts arising from overlapping projections could be a major problem in multi-Pinhole reconstruction, the cold-rod phantom study showed minimal loss of spatial resolution in multi-Pinhole systems, compared to a single-Pinhole system with the same Pinhole diameter. A quantitative study of neuroreceptor binding sites using a mouse brain phantom and low activity (37 MBq) showed that the multi-Pinhole system outperformed the single-Pinhole system by maintaining the mean and lowering the variance in the measured uptake ratio. Multi-Pinhole collimation can be used to reduce the injected dose and thereby reduce the radiation exposure to the animal. Results also suggest that the nine-Pinhole configuration shown in this paper is a good choice for mouse brain imaging.
-
Pinhole PET (pPET): a multi-Pinhole collimator insert for small animal SPECT imaging on PET cameras
IEEE Nuclear Science Symposium Conference Record 2005, 2005Co-Authors: Christopher Cardi, Mathew L. Thakur, Joel S. Karp, Paul D ActonAbstract:To effectively study small animal models of disease in vivo a wide range of PET and SPECT imaging agents need to be employed. In an effort to achieve high resolution and high sensitivity small animal SPECT imaging we propose the notion of using a multiple Pinhole insert in a PET scanner (pPET). Adapting PET scanners to enable Pinhole SPECT imaging is an attractive solution for many reasons. Most PET systems are full ring detectors which offer the potential for Pinhole configurations that fully sample an object without the need for complex detector rotation. Dual modality studies can be performed without moving the subject providing perfect spatial alignment. Furthermore, enabling SPECT imaging in a PET scanner makes financial sense by reducing the initial investment and maintenance costs. In this study we prove the feasibility of using a Pinhole insert to enable SPECT imaging in PET scanners. Simulations performed using the geometry of the Mosaic (Philips), a dedicated small animal PET scanner (Rdet=98.5 mm), show a variety of attractive Pinhole configurations offering a blend of resolution (to under 1.0 mm), sensitivity (up to 0.5%), field of view (up to 40 mm) and good image quality. Measurements with the Mosaic demonstrate that by raising the high voltage, to account for the lower light output, 140 keV gammas can be efficiently detected and adequately positioned for both GSO (gadolinium oxyorthosilicate) and LYSO (lutetium yttrium orthosilicate) scintillators. Initial imaging studies with a 12/spl times/1 (holes /spl times/ rows) collimator with 1.0 mm Pinholes at a 30 mm radius demonstrate the feasibility and show promising resolution (1.5 mm FWHM), good image quality, and a relatively large field of view.
Frans Van Der Have - One of the best experts on this subject based on the ideXlab platform.
-
absolute quantitative total body small animal spect with focusing Pinholes
European Journal of Nuclear Medicine and Molecular Imaging, 2010Co-Authors: Chao Wu, Frans Van Der Have, Brendan Vastenhouw, Rudi Dierckx, A M J Paans, Freek J BeekmanAbstract:Purpose In Pinhole SPECT, attenuation of the photon flux on trajectories between source and Pinholes affects quantitative accuracy of reconstructed images. Previously we introduced iterative methods that compensate for image degrading effects of detector and Pinhole blurring, Pinhole sensitivity and scatter for multi-Pinhole SPECT. The aim of this paper is (1) to investigate the accuracy of the Chang algorithm in rodents and (2) to present a practical Chang-based method using body outline contours obtained with optical cameras.
-
optimizing multi Pinhole spect geometries using an analytical model
Physics in Medicine and Biology, 2007Co-Authors: M.c.m. Rentmeester, Frans Van Der Have, Freek J BeekmanAbstract:State-of-the-art multi-Pinhole SPECT devices allow for sub-mm resolution imaging of radio-molecule distributions in small laboratory animals. The optimization of multi-Pinhole and detector geometries using simulations based on ray-tracing or Monte Carlo algorithms is time-consuming, particularly because many system parameters need to be varied. As an efficient alternative we develop a continuous analytical model of a Pinhole SPECT system with a stationary detector set-up, which we apply to focused imaging of a mouse. The model assumes that the multi-Pinhole collimator and the detector both have the shape of a spherical layer, and uses analytical expressions for effective Pinhole diameters, sensitivity and spatial resolution. For fixed fields-of-view, a Pinhole-diameter adapting feedback loop allows for the comparison of the system resolution of different systems at equal system sensitivity, and vice versa. The model predicts that (i) for optimal resolution or sensitivity the collimator layer with Pinholes should be placed as closely as possible around the animal given a fixed detector layer, (ii) with high-resolution detectors a resolution improvement up to 31% can be achieved compared to optimized systems, (iii) high-resolution detectors can be placed close to the collimator without significant resolution losses, (iv) interestingly, systems with a physical Pinhole diameter of 0 mm can have an excellent resolution when high-resolution detectors are used.
-
the Pinhole gateway to ultra high resolution three dimensional radionuclide imaging
European Journal of Nuclear Medicine and Molecular Imaging, 2007Co-Authors: Freek J Beekman, Frans Van Der HaveAbstract:Today the majority of clinical molecular imaging procedures are carried out with single-photon emitters and gamma cameras, in planar mode and single-photon emission computed tomography (SPECT) mode. Thanks to the development of advanced multi-Pinhole collimation technologies, SPECT imaging of small experimental animals is rapidly gaining in popularity. Whereas resolutions in routine clinical SPECT are typically larger than 1 cm (corresponding to >1,000 μl), it has recently proved possible to obtain spatial resolutions of about 0.35 mm (≈0.04 μl) in the mouse. Meanwhile, SPECT systems that promise an even better performance are under construction. The new systems are able to monitor functions in even smaller structures of the mouse than was possible with dedicated small animal positron emission tomography (≈1 mm resolution, corresponding to 1 μl). This paper provides a brief history of image formation with Pinholes and explains the principles of Pinhole imaging and Pinhole tomography and the basics of modern image reconstruction methods required for such systems. Some recently introduced ultra-high-resolution small animal SPECT instruments are discussed and new avenues for improving system performance are explored. This may lead to many completely new biomedical applications. We also demonstrate that clinical SPECT systems with focussing Pinhole gamma cameras will be able to produce images with a resolution that may become superior to that of PET for major clinical applications. A design study of a cardiac Pinhole SPECT system indicates that the heart can be imaged an order of magnitude faster or with much more detail than is possible with currently used parallel-hole SPECT (e.g. 3–4 mm instead of ≈8 mm system resolution).
-
penetration scatter and sensitivity in channel micro Pinholes for spect a monte carlo investigation
IEEE Transactions on Nuclear Science, 2006Co-Authors: Frans Van Der Have, Freek J BeekmanAbstract:Channel-edge Pinhole designs have been proposed in order to reduce the penetration of gamma rays through the edge of the Pinhole aperture. A characterization of penetration and scatter in the Pinhole aperture metal can be used in the design of small animal SPECT collimators or for model based corrections during micro-SPECT image reconstruction. In this study the penetration and scatter contributions of micro-Pinholes were compared for Tc-99m, I-123, and I-125 for knife-edges and channel-edges. To this end, Geant 4 Monte Carlo simulations of 0.3 mm and 0.5 mm diameter apertures with acceptance angles ranging from 20 to 60 degrees were performed. At perpendicular incidence of the photons, channel Pinholes had lower penetration and scatter fractions than did knife-edge Pinholes. This advantage disappeared at higher angles of incidence. In addition, the total sensitivity decreased substantially with increasing channel height. Planar projection images of a grid of spheres showed that channel-edge Pinholes resulted in a slightly higher spatial resolution than knife-edge Pinholes with an equal diameter, when combined with a high-resolution detector. However, the channel-edge Pinhole's sensitivity and Contrast Inverse Coefficient of Variation were lower than the knife edge Pinhole's at the edges of the detector. We conclude that channel Pinholes can result in lower imaging performance when used with non-perpendicular incidence photons because of loss of sensitivity
-
Continuous model of multi-Pinhole SPECT devices
IEEE Nuclear Science Symposium Conference Record 2005, 2005Co-Authors: M.c.m. Rentmeester, Frans Van Der Have, Freek J BeekmanAbstract:Recently multi-Pinhole SPECT systems have been proposed that allow for sub-mm resolution imaging in mice. The optimization of multi-Pinhole systems using ray-tracing or Monte Carlo simulation is extremely time consuming. As an alternative we develop an approximate continuous model of a SPECT system which we apply to focused Pinhole imaging of the mouse. In order to facilitate the use of analytical mathematical calculations the model assumes that the system consists of spherical layers. It uses analytical expressions of effective Pinhole diameters, sensitivity, and resolution. With a Pinhole-diameter adapting feedback loop that allows to compare system resolution at equal system sensitivity and vice versa the model predicts that (i) for optimal resolution Pinholes should be as close as possible to the animal, (ii) with high resolution (
