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Kim S.,University of California at San Francisco | McClish M.,RadiationMonitoring Devices Inc. | Alhassen F.,University of California at San Francisco | Seo Y.,University of California at San Francisco | And 2 more authors.
IEEE Transactions on Nuclear Science | Year: 2010

We demonstrate a position sensitive avalanche photodiode (PSAPD) based compact gamma camera for the application of small animal single photon emission computed tomography (SPECT). The silicon PSAPD with a two-dimensional resistive layer and four readout channels is implemented as a gamma ray detector to record the energy and position of radiation events from a radionuclide source. A 2 mm thick monolithic CsI:Tl scintillator is optically coupled to a PSAPD with a 8 mm × 8 mm active area, providing submillimeter intrinsic spatial resolution, high energy resolution (16% full-width half maximum at 140 keV) and high gain. A mouse heart phantom filled with an aqueous solution of 370 MBq 99Tc-pertechnetate (140 keV) was imaged using the PSAPD detector module and a tungsten knife-edge pinhole collimator with a 0.5 mm diameter aperture. The PSAPD detector module was cooled with cold nitrogen gas to suppress dark current shot noise. For each projection image of the mouse heart phantom, a rotated diagonal readout algorithm was used to calculate the position of radiation events and correct for pincushion distortion. The reconstructed image of the mouse heart phantom demonstrated reproducible image quality with submillimeter spatial resolution (0.7 mm), showing the feasibility of using the compact PSAPD-based gamma camera for a small animal SPECT system. © 2010 IEEE. Source


Sabet H.,RadiationMonitoring Devices Inc. | Prekas G.,RadiationMonitoring Devices Inc. | Breen M.,RadiationMonitoring Devices Inc. | Bhandari H.B.,RadiationMonitoring Devices Inc. | And 6 more authors.
IEEE Transactions on Nuclear Science | Year: 2012

We are developing a technique to fabricate high spatial resolution and cost-effective photon counting detectors using silicon photomultipliers (SiPMs) and microcolumnar structured scintillator. Photon counting detectors using SiPMs are of much interest to the gamma-and X-ray detector community, but they have limitations at low energy due to their dark noise. In this paper, we report on vapor deposition of CsI:Tl directly onto a SiPM, a technique that improves optical coupling and allows for detection of low energy gamma-and X-rays. It simultaneously addresses related issues of light loss and light spread in the scintillator, thereby improving the performance of the detector. Devices made by this technique may be used for both photon counting and gamma-and X-ray imaging. The SiPM used in this study comprises a 4 × 4 array of macropixels, each of which is 3.0 mm × 3.0 mm, with 3.36 mm pitch. This SiPM was placed inside a physical vapor deposition chamber and a 0.75 mm thick layer of microcolumnar CsI:Tl was grown on its surface without any damage. Scanning Electron micrographs (SEM) show highly oriented microcolumnar CsI:Tl structure orthogonal to the SiPM surface. These microcolumnar structures are excellent for channeling scintillation light to the SiPM and provide sub-macro-pixel resolution, which is now limited to the size of the macro-pixels. In this study, we report the performance characteristics of the resultant detector in terms of position sensitivity, energy discrimination, optical crosstalk, and signal-to-noise ratio. The performance of the detector is evaluated against that of other CsI:Tl/SiPM combinations, such as mechanically coupled monolithic and laser-pixelated CsI:Tl scintillators. Success of the techniquemay be gauged by the fact that the photopeak can be realized for a wide range of energies, including those of 241Am (60 keV) 57Co and (122 keV). © 2012 IEEE. Source

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