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Craig S. Levin - One of the best experts on this subject based on the ideXlab platform.
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Investigation of cooling structure design for PET detector Thermal Regulation methods
2016 IEEE Nuclear Science Symposium Medical Imaging Conference and Room-Temperature Semiconductor Detector Workshop (NSS MIC RTSD), 2016Co-Authors: Brian J. Lee, Chen-ming Chang, Inyong Kwon, Craig S. LevinAbstract:Temperature is an essential factor for stable performance of the positron emission tomography (PET). Some of the PET detector components produce significant heat (e.g. readout integrated circuits) that affects its performance. The temperature alters the breakdown voltage of photodetectors, which in turn affects the gain, cross talk, dark count rate and after-pulsing. One of the Thermal Regulation methods is to use an air/liquid cooling pipe embedded in a cold plate broadly distributing the temperature to the PC board; the gold vias in the board then conduct the temperature to the other side of the board. This paper concentrates on investigating the temperature distribution from various cooling structure configurations. The simulation software COMSOL was used with heat transfer and pipe flow modules to assess the Thermal behavior of the cooling system. Two types of cooling pipe arrangements were simulated; a simple and a more complex curve arrangement. For the cold plates, a ceramic (92 W/m-K) and a Thermally conductive plastic (10 W/m-K) were simulated. Full as well as “patchy” gold via configurations were also simulated. The simulation was performed for 300 seconds (real time) and the average and the standard deviation temperature of each SiPM was analyzed. With the complex cooling pipe arrangement, the temperature variation throughout all SiPMs was on average 37.9±5.2% higher for ceramic cold plates. For the cold plate materials, the ceramic showed 33.9±15.4% smaller Thermal variation and −1.1±0.6% lower temperature compared to the Thermally conductive plastic. The patchy vias resulted in 218.2±74.9% larger Thermal variation when compared to the patchy vias. In summary, we have simulated various cooling pipe designs, cold plates and gold via distribution configurations to analyze the temperature variation across a PET detector PC board. The Thermally conductive ceramic cold plate with as many vias as possible resulted in the most stable temperature variation.
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Thermal Regulation of tightly packed solid‐state photodetectors in a 1 mm3 resolution clinical PET system
Medical physics, 2014Co-Authors: David L. Freese, Arne Vandenbroucke, Derek Innes, Frances W. Y. Lau, David Hsu, Paul D. Reynolds, Craig S. LevinAbstract:Purpose: Silicon photodetectors are of significant interest for use in positron emission tomography (PET) systems due to their compact size, insensitivity to magnetic fields, and high quantum efficiency. However, one of their main disadvantages is fluctuations in temperature cause strong shifts in gain of the devices. PET system designs with high photodetector density suffer both increased Thermal density and constrained options for Thermally regulating the devices. This paper proposes a method of Thermally regulating densely packed silicon photodetectors in the context of a 1 mm{sup 3} resolution, high-sensitivity PET camera dedicated to breast imaging. Methods: The PET camera under construction consists of 2304 units, each containing two 8 × 8 arrays of 1 mm{sup 3} LYSO crystals coupled to two position sensitive avalanche photodiodes (PSAPD). A subsection of the proposed camera with 512 PSAPDs has been constructed. The proposed Thermal Regulation design uses water-cooled heat sinks, thermoelectric elements, and thermistors to measure and regulate the temperature of the PSAPDs in a novel manner. Active cooling elements, placed at the edge of the detector stack due to limited access, are controlled based on collective leakage current and temperature measurements in order to keep all the PSAPDs at a consistent temperature. Thismore » Thermal Regulation design is characterized for the temperature profile across the camera and for the time required for cooling changes to propagate across the camera. These properties guide the implementation of a software-based, cascaded proportional-integral-derivative control loop that controls the current through the Peltier elements by monitoring thermistor temperature and leakage current. The stability of leakage current, temperature within the system using this control loop is tested over a period of 14 h. The energy resolution is then measured over a period of 8.66 h. Finally, the consistency of PSAPD gain between independent operations of the camera over 10 days is tested. Results: The PET camera maintains a temperature of 18.00 ± 0.05 °C over the course of 12 h while the ambient temperature varied 0.61 °C, from 22.83 to 23.44 °C. The 511 keV photopeak energy resolution over a period of 8.66 h is measured to be 11.3% FWHM with a maximum photopeak fluctuation of 4 keV. Between measurements of PSAPD gain separated by at least 2 day, the maximum photopeak shift was 6 keV. Conclusions: The proposed Thermal Regulation scheme for tightly packed silicon photodetectors provides for stable operation of the constructed subsection of a PET camera over long durations of time. The energy resolution of the system is not degraded despite shifts in ambient temperature and photodetector heat generation. The Thermal Regulation scheme also provides a consistent operating environment between separate runs of the camera over different days. Inter-run consistency allows for reuse of system calibration parameters from study to study, reducing the time required to calibrate the system and hence to obtain a reconstructed image.« less
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Thermal Regulation of tightly packed solid state photodetectors in a 1 mm3 resolution clinical pet system
Medical Physics, 2014Co-Authors: David L. Freese, Arne Vandenbroucke, Derek Innes, Frances W. Y. Lau, David Hsu, Paul D. Reynolds, Craig S. LevinAbstract:Purpose: Silicon photodetectors are of significant interest for use in positron emission tomography (PET) systems due to their compact size, insensitivity to magnetic fields, and high quantum efficiency. However, one of their main disadvantages is fluctuations in temperature cause strong shifts in gain of the devices. PET system designs with high photodetector density suffer both increased Thermal density and constrained options for Thermally regulating the devices. This paper proposes a method of Thermally regulating densely packed silicon photodetectors in the context of a 1 mm{sup 3} resolution, high-sensitivity PET camera dedicated to breast imaging. Methods: The PET camera under construction consists of 2304 units, each containing two 8 × 8 arrays of 1 mm{sup 3} LYSO crystals coupled to two position sensitive avalanche photodiodes (PSAPD). A subsection of the proposed camera with 512 PSAPDs has been constructed. The proposed Thermal Regulation design uses water-cooled heat sinks, thermoelectric elements, and thermistors to measure and regulate the temperature of the PSAPDs in a novel manner. Active cooling elements, placed at the edge of the detector stack due to limited access, are controlled based on collective leakage current and temperature measurements in order to keep all the PSAPDs at a consistent temperature. Thismore » Thermal Regulation design is characterized for the temperature profile across the camera and for the time required for cooling changes to propagate across the camera. These properties guide the implementation of a software-based, cascaded proportional-integral-derivative control loop that controls the current through the Peltier elements by monitoring thermistor temperature and leakage current. The stability of leakage current, temperature within the system using this control loop is tested over a period of 14 h. The energy resolution is then measured over a period of 8.66 h. Finally, the consistency of PSAPD gain between independent operations of the camera over 10 days is tested. Results: The PET camera maintains a temperature of 18.00 ± 0.05 °C over the course of 12 h while the ambient temperature varied 0.61 °C, from 22.83 to 23.44 °C. The 511 keV photopeak energy resolution over a period of 8.66 h is measured to be 11.3% FWHM with a maximum photopeak fluctuation of 4 keV. Between measurements of PSAPD gain separated by at least 2 day, the maximum photopeak shift was 6 keV. Conclusions: The proposed Thermal Regulation scheme for tightly packed silicon photodetectors provides for stable operation of the constructed subsection of a PET camera over long durations of time. The energy resolution of the system is not degraded despite shifts in ambient temperature and photodetector heat generation. The Thermal Regulation scheme also provides a consistent operating environment between separate runs of the camera over different days. Inter-run consistency allows for reuse of system calibration parameters from study to study, reducing the time required to calibrate the system and hence to obtain a reconstructed image.« less
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Thermal Regulation for APDs in a 1 mm(3) resolution clinical PET camera: design, simulation and experimental verification.
Physics in medicine and biology, 2014Co-Authors: Jinjian Zhai, Arne Vandenbroucke, Craig S. LevinAbstract:We are developing a 1 mm3 resolution positron emission tomography camera dedicated to breast imaging. The camera collects high energy photons emitted from radioactively labeled agents introduced in the patients in order to detect molecular signatures of breast cancer. The camera comprises many layers of lutetium yttrium oxyorthosilicate (LYSO) scintillation crystals coupled to position sensitive avalanche photodiodes (PSAPDs). The main objectives of the studies presented in this paper are to investigate the temperature profile of the layers of LYSO–PSAPD detectors (a.k.a. 'fins') residing in the camera and to use these results to present the design of the Thermal Regulation system for the front end of the camera. The study was performed using both experimental methods and simulation. We investigated a design with a heat-dissipating fin. Three fin configurations are tested: fin with Al windows (FwW), fin without Al windows (FwoW) and fin with alumina windows (FwAW). A Fluent® simulation was conducted to study the experimentally inaccessible temperature of the PSAPDs. For the best configuration (FwW), the temperature difference from the center to a point near the edge is 1.0 K when 1.5 A current was applied to the Peltier elements. Those of FwoW and FwAW are 2.6 K and 1.7 K, respectively. We conclude that the design of a heat-dissipating fin configuration with 'aluminum windows' (FwW) that borders the scintillation crystal arrays of 16 adjacent detector modules has better heat dissipation capabilities than the design without 'aluminum windows' (FwoW) and the design with 'alumina windows' (FwAW), respectively.
David L. Freese - One of the best experts on this subject based on the ideXlab platform.
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Thermal Regulation of tightly packed solid‐state photodetectors in a 1 mm3 resolution clinical PET system
Medical physics, 2014Co-Authors: David L. Freese, Arne Vandenbroucke, Derek Innes, Frances W. Y. Lau, David Hsu, Paul D. Reynolds, Craig S. LevinAbstract:Purpose: Silicon photodetectors are of significant interest for use in positron emission tomography (PET) systems due to their compact size, insensitivity to magnetic fields, and high quantum efficiency. However, one of their main disadvantages is fluctuations in temperature cause strong shifts in gain of the devices. PET system designs with high photodetector density suffer both increased Thermal density and constrained options for Thermally regulating the devices. This paper proposes a method of Thermally regulating densely packed silicon photodetectors in the context of a 1 mm{sup 3} resolution, high-sensitivity PET camera dedicated to breast imaging. Methods: The PET camera under construction consists of 2304 units, each containing two 8 × 8 arrays of 1 mm{sup 3} LYSO crystals coupled to two position sensitive avalanche photodiodes (PSAPD). A subsection of the proposed camera with 512 PSAPDs has been constructed. The proposed Thermal Regulation design uses water-cooled heat sinks, thermoelectric elements, and thermistors to measure and regulate the temperature of the PSAPDs in a novel manner. Active cooling elements, placed at the edge of the detector stack due to limited access, are controlled based on collective leakage current and temperature measurements in order to keep all the PSAPDs at a consistent temperature. Thismore » Thermal Regulation design is characterized for the temperature profile across the camera and for the time required for cooling changes to propagate across the camera. These properties guide the implementation of a software-based, cascaded proportional-integral-derivative control loop that controls the current through the Peltier elements by monitoring thermistor temperature and leakage current. The stability of leakage current, temperature within the system using this control loop is tested over a period of 14 h. The energy resolution is then measured over a period of 8.66 h. Finally, the consistency of PSAPD gain between independent operations of the camera over 10 days is tested. Results: The PET camera maintains a temperature of 18.00 ± 0.05 °C over the course of 12 h while the ambient temperature varied 0.61 °C, from 22.83 to 23.44 °C. The 511 keV photopeak energy resolution over a period of 8.66 h is measured to be 11.3% FWHM with a maximum photopeak fluctuation of 4 keV. Between measurements of PSAPD gain separated by at least 2 day, the maximum photopeak shift was 6 keV. Conclusions: The proposed Thermal Regulation scheme for tightly packed silicon photodetectors provides for stable operation of the constructed subsection of a PET camera over long durations of time. The energy resolution of the system is not degraded despite shifts in ambient temperature and photodetector heat generation. The Thermal Regulation scheme also provides a consistent operating environment between separate runs of the camera over different days. Inter-run consistency allows for reuse of system calibration parameters from study to study, reducing the time required to calibrate the system and hence to obtain a reconstructed image.« less
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Thermal Regulation of tightly packed solid state photodetectors in a 1 mm3 resolution clinical pet system
Medical Physics, 2014Co-Authors: David L. Freese, Arne Vandenbroucke, Derek Innes, Frances W. Y. Lau, David Hsu, Paul D. Reynolds, Craig S. LevinAbstract:Purpose: Silicon photodetectors are of significant interest for use in positron emission tomography (PET) systems due to their compact size, insensitivity to magnetic fields, and high quantum efficiency. However, one of their main disadvantages is fluctuations in temperature cause strong shifts in gain of the devices. PET system designs with high photodetector density suffer both increased Thermal density and constrained options for Thermally regulating the devices. This paper proposes a method of Thermally regulating densely packed silicon photodetectors in the context of a 1 mm{sup 3} resolution, high-sensitivity PET camera dedicated to breast imaging. Methods: The PET camera under construction consists of 2304 units, each containing two 8 × 8 arrays of 1 mm{sup 3} LYSO crystals coupled to two position sensitive avalanche photodiodes (PSAPD). A subsection of the proposed camera with 512 PSAPDs has been constructed. The proposed Thermal Regulation design uses water-cooled heat sinks, thermoelectric elements, and thermistors to measure and regulate the temperature of the PSAPDs in a novel manner. Active cooling elements, placed at the edge of the detector stack due to limited access, are controlled based on collective leakage current and temperature measurements in order to keep all the PSAPDs at a consistent temperature. Thismore » Thermal Regulation design is characterized for the temperature profile across the camera and for the time required for cooling changes to propagate across the camera. These properties guide the implementation of a software-based, cascaded proportional-integral-derivative control loop that controls the current through the Peltier elements by monitoring thermistor temperature and leakage current. The stability of leakage current, temperature within the system using this control loop is tested over a period of 14 h. The energy resolution is then measured over a period of 8.66 h. Finally, the consistency of PSAPD gain between independent operations of the camera over 10 days is tested. Results: The PET camera maintains a temperature of 18.00 ± 0.05 °C over the course of 12 h while the ambient temperature varied 0.61 °C, from 22.83 to 23.44 °C. The 511 keV photopeak energy resolution over a period of 8.66 h is measured to be 11.3% FWHM with a maximum photopeak fluctuation of 4 keV. Between measurements of PSAPD gain separated by at least 2 day, the maximum photopeak shift was 6 keV. Conclusions: The proposed Thermal Regulation scheme for tightly packed silicon photodetectors provides for stable operation of the constructed subsection of a PET camera over long durations of time. The energy resolution of the system is not degraded despite shifts in ambient temperature and photodetector heat generation. The Thermal Regulation scheme also provides a consistent operating environment between separate runs of the camera over different days. Inter-run consistency allows for reuse of system calibration parameters from study to study, reducing the time required to calibrate the system and hence to obtain a reconstructed image.« less
Arne Vandenbroucke - One of the best experts on this subject based on the ideXlab platform.
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Thermal Regulation of tightly packed solid‐state photodetectors in a 1 mm3 resolution clinical PET system
Medical physics, 2014Co-Authors: David L. Freese, Arne Vandenbroucke, Derek Innes, Frances W. Y. Lau, David Hsu, Paul D. Reynolds, Craig S. LevinAbstract:Purpose: Silicon photodetectors are of significant interest for use in positron emission tomography (PET) systems due to their compact size, insensitivity to magnetic fields, and high quantum efficiency. However, one of their main disadvantages is fluctuations in temperature cause strong shifts in gain of the devices. PET system designs with high photodetector density suffer both increased Thermal density and constrained options for Thermally regulating the devices. This paper proposes a method of Thermally regulating densely packed silicon photodetectors in the context of a 1 mm{sup 3} resolution, high-sensitivity PET camera dedicated to breast imaging. Methods: The PET camera under construction consists of 2304 units, each containing two 8 × 8 arrays of 1 mm{sup 3} LYSO crystals coupled to two position sensitive avalanche photodiodes (PSAPD). A subsection of the proposed camera with 512 PSAPDs has been constructed. The proposed Thermal Regulation design uses water-cooled heat sinks, thermoelectric elements, and thermistors to measure and regulate the temperature of the PSAPDs in a novel manner. Active cooling elements, placed at the edge of the detector stack due to limited access, are controlled based on collective leakage current and temperature measurements in order to keep all the PSAPDs at a consistent temperature. Thismore » Thermal Regulation design is characterized for the temperature profile across the camera and for the time required for cooling changes to propagate across the camera. These properties guide the implementation of a software-based, cascaded proportional-integral-derivative control loop that controls the current through the Peltier elements by monitoring thermistor temperature and leakage current. The stability of leakage current, temperature within the system using this control loop is tested over a period of 14 h. The energy resolution is then measured over a period of 8.66 h. Finally, the consistency of PSAPD gain between independent operations of the camera over 10 days is tested. Results: The PET camera maintains a temperature of 18.00 ± 0.05 °C over the course of 12 h while the ambient temperature varied 0.61 °C, from 22.83 to 23.44 °C. The 511 keV photopeak energy resolution over a period of 8.66 h is measured to be 11.3% FWHM with a maximum photopeak fluctuation of 4 keV. Between measurements of PSAPD gain separated by at least 2 day, the maximum photopeak shift was 6 keV. Conclusions: The proposed Thermal Regulation scheme for tightly packed silicon photodetectors provides for stable operation of the constructed subsection of a PET camera over long durations of time. The energy resolution of the system is not degraded despite shifts in ambient temperature and photodetector heat generation. The Thermal Regulation scheme also provides a consistent operating environment between separate runs of the camera over different days. Inter-run consistency allows for reuse of system calibration parameters from study to study, reducing the time required to calibrate the system and hence to obtain a reconstructed image.« less
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Thermal Regulation of tightly packed solid state photodetectors in a 1 mm3 resolution clinical pet system
Medical Physics, 2014Co-Authors: David L. Freese, Arne Vandenbroucke, Derek Innes, Frances W. Y. Lau, David Hsu, Paul D. Reynolds, Craig S. LevinAbstract:Purpose: Silicon photodetectors are of significant interest for use in positron emission tomography (PET) systems due to their compact size, insensitivity to magnetic fields, and high quantum efficiency. However, one of their main disadvantages is fluctuations in temperature cause strong shifts in gain of the devices. PET system designs with high photodetector density suffer both increased Thermal density and constrained options for Thermally regulating the devices. This paper proposes a method of Thermally regulating densely packed silicon photodetectors in the context of a 1 mm{sup 3} resolution, high-sensitivity PET camera dedicated to breast imaging. Methods: The PET camera under construction consists of 2304 units, each containing two 8 × 8 arrays of 1 mm{sup 3} LYSO crystals coupled to two position sensitive avalanche photodiodes (PSAPD). A subsection of the proposed camera with 512 PSAPDs has been constructed. The proposed Thermal Regulation design uses water-cooled heat sinks, thermoelectric elements, and thermistors to measure and regulate the temperature of the PSAPDs in a novel manner. Active cooling elements, placed at the edge of the detector stack due to limited access, are controlled based on collective leakage current and temperature measurements in order to keep all the PSAPDs at a consistent temperature. Thismore » Thermal Regulation design is characterized for the temperature profile across the camera and for the time required for cooling changes to propagate across the camera. These properties guide the implementation of a software-based, cascaded proportional-integral-derivative control loop that controls the current through the Peltier elements by monitoring thermistor temperature and leakage current. The stability of leakage current, temperature within the system using this control loop is tested over a period of 14 h. The energy resolution is then measured over a period of 8.66 h. Finally, the consistency of PSAPD gain between independent operations of the camera over 10 days is tested. Results: The PET camera maintains a temperature of 18.00 ± 0.05 °C over the course of 12 h while the ambient temperature varied 0.61 °C, from 22.83 to 23.44 °C. The 511 keV photopeak energy resolution over a period of 8.66 h is measured to be 11.3% FWHM with a maximum photopeak fluctuation of 4 keV. Between measurements of PSAPD gain separated by at least 2 day, the maximum photopeak shift was 6 keV. Conclusions: The proposed Thermal Regulation scheme for tightly packed silicon photodetectors provides for stable operation of the constructed subsection of a PET camera over long durations of time. The energy resolution of the system is not degraded despite shifts in ambient temperature and photodetector heat generation. The Thermal Regulation scheme also provides a consistent operating environment between separate runs of the camera over different days. Inter-run consistency allows for reuse of system calibration parameters from study to study, reducing the time required to calibrate the system and hence to obtain a reconstructed image.« less
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Thermal Regulation for APDs in a 1 mm(3) resolution clinical PET camera: design, simulation and experimental verification.
Physics in medicine and biology, 2014Co-Authors: Jinjian Zhai, Arne Vandenbroucke, Craig S. LevinAbstract:We are developing a 1 mm3 resolution positron emission tomography camera dedicated to breast imaging. The camera collects high energy photons emitted from radioactively labeled agents introduced in the patients in order to detect molecular signatures of breast cancer. The camera comprises many layers of lutetium yttrium oxyorthosilicate (LYSO) scintillation crystals coupled to position sensitive avalanche photodiodes (PSAPDs). The main objectives of the studies presented in this paper are to investigate the temperature profile of the layers of LYSO–PSAPD detectors (a.k.a. 'fins') residing in the camera and to use these results to present the design of the Thermal Regulation system for the front end of the camera. The study was performed using both experimental methods and simulation. We investigated a design with a heat-dissipating fin. Three fin configurations are tested: fin with Al windows (FwW), fin without Al windows (FwoW) and fin with alumina windows (FwAW). A Fluent® simulation was conducted to study the experimentally inaccessible temperature of the PSAPDs. For the best configuration (FwW), the temperature difference from the center to a point near the edge is 1.0 K when 1.5 A current was applied to the Peltier elements. Those of FwoW and FwAW are 2.6 K and 1.7 K, respectively. We conclude that the design of a heat-dissipating fin configuration with 'aluminum windows' (FwW) that borders the scintillation crystal arrays of 16 adjacent detector modules has better heat dissipation capabilities than the design without 'aluminum windows' (FwoW) and the design with 'alumina windows' (FwAW), respectively.
Jorge R. Frade - One of the best experts on this subject based on the ideXlab platform.
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Highly conducting core–shell phase change materials for Thermal Regulation
Applied Thermal Engineering, 2014Co-Authors: Nuno Vitorino, João C.c. Abrantes, Jorge R. FradeAbstract:Abstract A core–shell model has been derived for microstructural design of PCM-based composites with optimized 3-dimensional organization of a conducting phase, and a novel method was developed to process self-assembled core–shell composites for Thermal Regulation or heat storage. The method was based on emulsification of graphite suspensions in melted paraffin yielding a core–shell microstructure based on self-organisation of graphite platelets with preferential orientation; this allows remarkable enhancement of Thermal conductivity, which increases by at least one order of magnitude for 5 vol% graphite addition. The microstructure of the graphite shell remains stable upon repeated cycling above and below the melting temperature of the paraffin, and shape stabilization is also retained, even without external encapsulation. One confirm that the levels of Thermal conductivity of these phase change materials is sufficient for latent heat discharge from relatively large spherical samples to surrounding air.
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Highly conducting core-shell phase change materials for Thermal Regulation
Applied Thermal Engineering, 2014Co-Authors: Nuno Vitorino, João C.c. Abrantes, Jorge R. FradeAbstract:A core-shell model has been derived for microstructural design of PCM-based composites with optimized 3-dimensional organization of a conducting phase, and a novel method was developed to process self-assembled core-shell composites for Thermal Regulation or heat storage. The method was based on emulsification of graphite suspensions in melted paraffin yielding a core-shell microstructure based on self-organisation of graphite platelets with preferential orientation; this allows remarkable enhancement of Thermal conductivity, which increases by at least one order of magnitude for 5 vol% graphite addition. The microstructure of the graphite shell remains stable upon repeated cycling above and below the melting temperature of the paraffin, and shape stabilization is also retained, even without external encapsulation. One confirm that the levels of Thermal conductivity of these phase change materials is sufficient for latent heat discharge from relatively large spherical samples to surrounding air. © 2014 Elsevier Ltd. All rights reserved.
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Highly conducting core–shell phase change materials for Thermal Regulation
Applied Thermal Engineering, 2014Co-Authors: Nuno Vitorino, João C.c. Abrantes, Jorge R. FradeAbstract:A core shell model has been derived for microstructural design of PCM-based composites with optimized 3-dimensional organization of a conducting phase, and a novel method was developed to process self-assembled core shell composites for Thermal Regulation or heat storage. The method was based on emulsification of graphite suspensions in melted paraffin yielding a core shell microstructure based on self-organisation of graphite platelets with preferential orientation; this allows remarkable enhancement of Thermal conductivity, which increases by at least one order of magnitude for 5 vol% graphite addition. The microstructure of the graphite shell remains stable upon repeated cycling above and below the melting temperature of the paraffin, and shape stabilization is also retained, even without external encapsulation. One confirm that the levels of Thermal conductivity of these phase change materials is sufficient for latent heat discharge from relatively large spherical samples to surrounding air. (C) 2014 Elsevier Ltd. All rights reserved
Frances W. Y. Lau - One of the best experts on this subject based on the ideXlab platform.
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Thermal Regulation of tightly packed solid‐state photodetectors in a 1 mm3 resolution clinical PET system
Medical physics, 2014Co-Authors: David L. Freese, Arne Vandenbroucke, Derek Innes, Frances W. Y. Lau, David Hsu, Paul D. Reynolds, Craig S. LevinAbstract:Purpose: Silicon photodetectors are of significant interest for use in positron emission tomography (PET) systems due to their compact size, insensitivity to magnetic fields, and high quantum efficiency. However, one of their main disadvantages is fluctuations in temperature cause strong shifts in gain of the devices. PET system designs with high photodetector density suffer both increased Thermal density and constrained options for Thermally regulating the devices. This paper proposes a method of Thermally regulating densely packed silicon photodetectors in the context of a 1 mm{sup 3} resolution, high-sensitivity PET camera dedicated to breast imaging. Methods: The PET camera under construction consists of 2304 units, each containing two 8 × 8 arrays of 1 mm{sup 3} LYSO crystals coupled to two position sensitive avalanche photodiodes (PSAPD). A subsection of the proposed camera with 512 PSAPDs has been constructed. The proposed Thermal Regulation design uses water-cooled heat sinks, thermoelectric elements, and thermistors to measure and regulate the temperature of the PSAPDs in a novel manner. Active cooling elements, placed at the edge of the detector stack due to limited access, are controlled based on collective leakage current and temperature measurements in order to keep all the PSAPDs at a consistent temperature. Thismore » Thermal Regulation design is characterized for the temperature profile across the camera and for the time required for cooling changes to propagate across the camera. These properties guide the implementation of a software-based, cascaded proportional-integral-derivative control loop that controls the current through the Peltier elements by monitoring thermistor temperature and leakage current. The stability of leakage current, temperature within the system using this control loop is tested over a period of 14 h. The energy resolution is then measured over a period of 8.66 h. Finally, the consistency of PSAPD gain between independent operations of the camera over 10 days is tested. Results: The PET camera maintains a temperature of 18.00 ± 0.05 °C over the course of 12 h while the ambient temperature varied 0.61 °C, from 22.83 to 23.44 °C. The 511 keV photopeak energy resolution over a period of 8.66 h is measured to be 11.3% FWHM with a maximum photopeak fluctuation of 4 keV. Between measurements of PSAPD gain separated by at least 2 day, the maximum photopeak shift was 6 keV. Conclusions: The proposed Thermal Regulation scheme for tightly packed silicon photodetectors provides for stable operation of the constructed subsection of a PET camera over long durations of time. The energy resolution of the system is not degraded despite shifts in ambient temperature and photodetector heat generation. The Thermal Regulation scheme also provides a consistent operating environment between separate runs of the camera over different days. Inter-run consistency allows for reuse of system calibration parameters from study to study, reducing the time required to calibrate the system and hence to obtain a reconstructed image.« less
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Thermal Regulation of tightly packed solid state photodetectors in a 1 mm3 resolution clinical pet system
Medical Physics, 2014Co-Authors: David L. Freese, Arne Vandenbroucke, Derek Innes, Frances W. Y. Lau, David Hsu, Paul D. Reynolds, Craig S. LevinAbstract:Purpose: Silicon photodetectors are of significant interest for use in positron emission tomography (PET) systems due to their compact size, insensitivity to magnetic fields, and high quantum efficiency. However, one of their main disadvantages is fluctuations in temperature cause strong shifts in gain of the devices. PET system designs with high photodetector density suffer both increased Thermal density and constrained options for Thermally regulating the devices. This paper proposes a method of Thermally regulating densely packed silicon photodetectors in the context of a 1 mm{sup 3} resolution, high-sensitivity PET camera dedicated to breast imaging. Methods: The PET camera under construction consists of 2304 units, each containing two 8 × 8 arrays of 1 mm{sup 3} LYSO crystals coupled to two position sensitive avalanche photodiodes (PSAPD). A subsection of the proposed camera with 512 PSAPDs has been constructed. The proposed Thermal Regulation design uses water-cooled heat sinks, thermoelectric elements, and thermistors to measure and regulate the temperature of the PSAPDs in a novel manner. Active cooling elements, placed at the edge of the detector stack due to limited access, are controlled based on collective leakage current and temperature measurements in order to keep all the PSAPDs at a consistent temperature. Thismore » Thermal Regulation design is characterized for the temperature profile across the camera and for the time required for cooling changes to propagate across the camera. These properties guide the implementation of a software-based, cascaded proportional-integral-derivative control loop that controls the current through the Peltier elements by monitoring thermistor temperature and leakage current. The stability of leakage current, temperature within the system using this control loop is tested over a period of 14 h. The energy resolution is then measured over a period of 8.66 h. Finally, the consistency of PSAPD gain between independent operations of the camera over 10 days is tested. Results: The PET camera maintains a temperature of 18.00 ± 0.05 °C over the course of 12 h while the ambient temperature varied 0.61 °C, from 22.83 to 23.44 °C. The 511 keV photopeak energy resolution over a period of 8.66 h is measured to be 11.3% FWHM with a maximum photopeak fluctuation of 4 keV. Between measurements of PSAPD gain separated by at least 2 day, the maximum photopeak shift was 6 keV. Conclusions: The proposed Thermal Regulation scheme for tightly packed silicon photodetectors provides for stable operation of the constructed subsection of a PET camera over long durations of time. The energy resolution of the system is not degraded despite shifts in ambient temperature and photodetector heat generation. The Thermal Regulation scheme also provides a consistent operating environment between separate runs of the camera over different days. Inter-run consistency allows for reuse of system calibration parameters from study to study, reducing the time required to calibrate the system and hence to obtain a reconstructed image.« less
