Thermal regulation of tightly packed solid‐state photodetectors in a 1 mm3 resolution clinical PET system

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Title:
Thermal regulation of tightly packed solid‐state photodetectors in a 1 mm3 resolution clinical PET system
Author: Freese, D. L ; Vandenbroucke, A ; Innes, D ; Lau, F. W. Y ; Hsu, D. F. C ; Reynolds, P. D ; Levin, Craig S
Subjects: Resistors ; three‐term control ; heat sinks ; Scintigraphy ; Leakage currents ; Non‐adjustable resistors formed as one or more layers or coatings; Non‐adjustable resistors made from powdered conducting material or powdered semi‐conducting material with or without insulating material ; cameras ; Digital computing or data processing equipment or methods, specially adapted for specific applications ; photodetectors ; Semiconductor devices sensitive to infra‐red radiation, light, electromagnetic radiation of shorter wavelength, or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof ; avalanche photodiodes ; Standards and calibration ; Devices sensitive to infra‐red, visible or ultra‐violet radiation ; temperature ; Details of cameras or camera bodies; Accessories therefor ; Image detection systems ; calibration ; image resolution ; medical image processing ; Peltier effect ; Transforming light or analogous information into electric information ; position sensitive avalanche photodiode (PSAPD) ; Reconstruction ; Positron emission tomography (PET) ; temperature measurement ; Photodetectors (including infrared and CCD detectors) ; Electric measurements ; thermistors ; image reconstruction ; Biological material, e.g. blood, urine; Haemocytometers ; the potential barrier working in avalanche mode, e.g. avalanche photodiode ; Including semiconductor components sensitive to infra‐red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation ; Refrigeration or cooling; Combined heating and refrigeration systems; Heat pump systems; Manufacture or storage of ice; Liquefaction or solidification of gases ; Measuring temperature; Measuring quantity of heat; Thermally‐sensitive elements not otherwise provided for ; positron emission mammography (PEM) ; silicon ; Photometry, e.g. photographic exposure meter ; Measuring half‐life of a radioactive substance ; Image data processing or generation, in general ; Calibrating of instruments or apparatus ; cooling ; Testing or calibrating of apparatus or arrangements provided for in groups G01D1/00 to G01D15/00 ; avalanche photodiode (APD) ; positron emission tomography ; Spatial resolution ; positron emission tomography (PET) ; Nuclear Medicine Physics
Is Part Of: Medical physics (Lancaster), 2015-01, Vol.42 (1), p.305-313
Description: 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 mm3 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 mm3 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. This 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.
Publisher: American Association of Physicists in Medicine
Language: English
Identifier: ISSN: 0094-2405
EISSN: 2473-4209
DOI: 10.1118/1.4903889
PMID: 25563270
Source: Alma/SFX Local Collection
Wiley Online Library Database Model 2017

Thermal regulation of tightly packed solid‐state photodetectors in a 1 mm3 resolution clinical PET system

Freese, D. L ; Vandenbroucke, A ; Innes, D ; Lau, F. W. Y ; Hsu, D. F. C ; Reynolds, P. D ; Levin, Craig S

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