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ABSTRACT: We have designed position sensitive solid-state photomultipliers (PS-SSPM) using a complementary metal-oxide-semiconductor (CMOS) process. Four variations of the PS-SSPM design were fabricated, however, one of the variations did not function properly. The remaining three functional variations were characterized for their energy and coincidence timing resolution, spatial resolution, and scintillator array imaging. Each PS-SSPM is 1.5 × 1.5 mm<sup>2</sup>, however, each device has different micro-pixel geometries and different micro-pixel electrical readout for event position sensing. When coupled to 1 × 1 × 20 mm<sup>3</sup> LYSO, the energy resolution at 511 keV was measured as a function of bias. The same LYSO scintillator was used to measure the coincidence timing resolution. Results between the PS-SSPMs varied from 2.0 ns to 0.9 ns (FWHM) at 511 keV. Spatial resolution studies were conducted using a focused (15 μm beam spot diameter) pulsed 635 nm diode laser. For each PS-SSPM, the X and Y spatial resolution was measured between 70 and 75 μm (FWHM). Lastly, scintillator array images were generated using a CsI:Tl and LYSO array having 300 × 300 μm<sup>2</sup> and 500 × 500 μm<sup>2</sup> pixels respectively.
IEEE Transactions on Nuclear Science 09/2010; · 1.45 Impact Factor
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ABSTRACT: We present the performance of a compact PET detector module with a depth-of-interaction (DOI) capability based on a LYSO scintillator array coupled at both ends to CMOS solid state photomultipliers (SSPM). In this paper we present flood imaging, energy resolution, coincidence timing and DOI resolution results for a prototype PET detector module consisting of a 4 Ã 4 block of LYSO scintillators, each crystal 3 measuring 1.43 Ã 1.43 Ã 20 mm<sup>3</sup> coupled to 4 Ã 4 array of SSPMs, 2 each SSPM element is 1.5 Ã 1.5 mm<sup>2</sup>. All 16 elements in the flood 22 image recorded with <sup>22</sup>Na gamma-ray source at all depths were clearly visible and well separated from each other. The measured FWHM energy resolution with 511 keV gamma rays for all crystals in the array ranged between 13% - 17% (FWHM). The timing resolution measured for the complete detector module in coincidence with LYSO-PMT detector was 2.3 ns (FWHM) and for the individual crystals ranged between 1.1 ns - 1.3 ns (FWHM). The DOI resolution measured for all crystals in the array was ranged between 2.3 mm - 2.9 mm.
Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 12/2009
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ABSTRACT: Excellent spatial resolution is a requirement for preclinical PET imaging. In order to achieve spatial resolution of significantly better than one millimeter, an appealing possibility is to employ direct detector materials, such as cadmium telluride (CdTe). Prototype thin orthogonal strip detectors have been developed for testing. They have dimensions of 20 mm by 20 mm and are 0.5 mm thick, and have strips of 0.5 mm pitch on one side and 2.5 mm pitch on the other. Results are presented for the energy resolution (3% at 511 keV), intrinsic position resolution (equal to the 0.5 mm strip pitch), and timing resolution (3 ns FWHM in coincidence with an LSO detector, 8 ns FWHM for coincidence of two CdTe detectors) of the detectors. A PET scanner design is proposed using blocks made of the CdTe strip detectors, oriented in the blocks with their thin edges toward the center of the scanner. Simulation results suggest that this scanner, using a threshold of 250 keV, would have a sensitivity of 3.4% for a point source at its center.
IEEE Transactions on Nuclear Science 07/2008; · 1.45 Impact Factor
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ABSTRACT: In this paper we present experimental results obtained with an orthogonal strip CdTe detector designed for application to small animal PET. The detector was designed to provide timing resolution acceptable for small animal PET, depth of interaction information and spatial resolution superior to scintillator based detectors. A CdTe sample of 20times20 mm<sup>2</sup> area and 0.5 mm thickness was patterned with strips of 0.5-mm pitch on one 20times20 mm<sup>2</sup> face. In a small animal PET detector ring the 511 keV gamma-rays would be incident on the edge of the device (i.e., 0.5times20 mm<sup>2</sup> face) and encounter 20-mm depth, providing reasonably high stopping efficiency. The strips with 0.5-mm pitch on the 20times20 mm<sup>2</sup> face (in combination with the device thickness of 0.5-mm) would provide identification of the event in an effective pixel size of 0.5times0.5 mm<sup>2</sup>. The other 20times20 mm<sup>2</sup> face of the device has coarser strips with 2.0-mm width (2.5-mm pitch) in the direction orthogonal to the finer 0.5-mm strips. These 2-mm strips provide the depth of interaction (DOI) for the 511 keV gamma-rays. Since the overall thickness between the electrodes is only 0.5-mm, fast and efficient collection of electrons and holes is possible, resulting in high energy and timing resolution. Pulse height spectra under <sup>22</sup>Na irradiation, coincidence timing resolution and detector response to a collimated source are presented.
Nuclear Science Symposium Conference Record, 2006. IEEE; 12/2006
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ABSTRACT: A CMOS solid-state photomultiplier (SSPM) coupled to a scintillation crystal uses an array of CMOS Geiger-mode avalanche photodiode (GPD) pixels to collect light and produce a signal proportional to the energy of the radiation. Each pixel acts as a binary photon detector, but the summed output is an analog representation of the total photon intensity. We have successfully fabricated arrays of GPD pixels in a CMOS environment, which makes possible the production of miniaturized arrays integrated with the detector electronics in a small silicon chip. In this work, we compare designs for the SSPM detector and present preliminary results in constructing a position-sensitive solid-state photomultiplier (PS-SSPM) using a commercially available CMOS process. The prototype arrays utilize a resistor network to provide a position-sensitive readout of the array. One pixel design achieves maximum detection efficiency for 632-nm photons approaching 20% with a room temperature dark count rate of less then 1 kHz for a 30-mum-diameter pixel. Pair-wise cross talk was measured to be less than 2% for 150 mum pixel spacing
Nuclear Science Symposium Conference Record, 2005 IEEE; 11/2005
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ABSTRACT: In this paper, investigation of position sensitive avalanche photodiodes (PSAPDs) as optical detectors for reading out segmented scintillation arrays of LSO in high resolution PET modules is reported. PSAPDs with 8×8 mm<sup>2</sup> and 14×14 mm<sup>2</sup> area have been characterized with single LSO crystals and arrays. Energy resolution of 19% (FWHM) for 511 keV γ-rays and coincidence timing resolution of ∼3 ns (FWHM) have been recorded with PSAPD coupled to 1×1×20 mm<sup>3</sup> LSO detectors. Flood histogram studies have been successfully conducted by coupling multi-element element LSO arrays (1 mm pixels, 20 mm tall) to the PSAPDs. Finally, depth of interaction (DOI) resolution of <4.5 mm (FWHM) has been measured by coupling two PSAPDs on opposite ends of a 20 mm long LSO crystal with a 1×1 mm<sup>2</sup> cross section. Based on these results, PSAPDs appear to be promising for high resolution PET. An important advantage of these PSAPDs is significant reduction in electronic readout requirements.
IEEE Transactions on Nuclear Science 03/2004; · 1.45 Impact Factor
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ABSTRACT: We report on proof-of-principle measurements of alpha-gamma angular correlations in the decay of <sup>224</sup>Ra, using a position-sensitive avalanche photo-diode for detecting alpha particles and a planar germanium double-sided strip detector for detecting gamma rays. The excellent position resolutions of both detectors allow close positioning of the radiation source to the detectors, covering a large angular range in a single configuration, thus enhancing efficiency in a compact geometry.
Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE;
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ABSTRACT: We have designed and developed a complementary metal-oxide-semiconductor (CMOS) solid-state photomultiplier (SSPM). We have studied this novel SSPM as a readout of LYSO scintillator for use in positron emission tomography (PET). Here we present energy resolution, coincidence timing resolution, depth of interaction measurements and flood imaging studies with SSPMs coupled to LYSO seintilators. Two different sizes, 3 x 3 mm<sup>2</sup> and 1.5 x 1.5 mm<sup>2</sup> SSPMs were studied. The measured FWHM energy resolution with 511 keV gamma rays was 22% for the detector consisting 3 x 3 mm<sup>2</sup> SSPM coupled to a 3 x 3 x 15 mm<sup>3</sup> LYSO and 11.2 % for the detector consisting 1.5 x 1.5 mm<sup>2</sup> SSPM coupled to 1.5 x 1.5 x 10 mm<sup>3</sup> LYSO. The timing resolution measured was 1.8 ns for the 3 x 3 mm<sup>2</sup> detector in coincidence with a detector consisting LSO coupled to PMT. The coincidence timing resolution was 530 ps for 1.5 x 1.5 mm<sup>2</sup> detector. The measured depth-of-interaction resolution by coupling two 1.5 x 1.5 mm<sup>2</sup> SSPMs on opposite ends of a 1.5 x 1.5 x 20 mm<sup>3</sup> LYSO scintillator was 2.5 mm. The flood histogram was recorded with a 4 x 4 LYSO array, each element measuring 1.5 x 1.5 x 15 mm<sup>3</sup> coupled to a position sensitive SSPM (PS-SSPM) consist of a 4 x 4 array of SSPM elements. The flood image was distortion free, all 16 elements were clearly visible and well separated from each other.
Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE;
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ABSTRACT: The solid-state photomultiplier (SSPM) is a relatively new semiconductor based photodetector that, by using hundreds of micro silicon Geiger APDs, possesses high gain (105–106) and low noise while needing only low voltage (40–60 V) to operate. The fast response and high intrinsic gain of SSPMs makes them attractive for timing applications, in particular for positron emission tomography (PET). Here we present the results from the characterization of a SSPM (SSPM-050701GR-TO18, Photonique SA). Several intrinsic SSPM characteristics were measured such as gain, dark noise, and linearity. Single photon spectra were also collected. Additionally, scintillation studies were performed. The SSPM was coupled to CsI:Tl and LSO scintillation crystals and exposed to various common laboratory radionuclides to measure photopeak energy resolutions. The linearity of the SSPM, when coupled with a scintillator, was also measured. Using a 22Na source (511 keV annihilation photons) and LSO, the SSPM FWHM energy resolution is 14.4%±0.2% and the estimated coincidence FWHM timing resolution is .
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
