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Bergeron M.,Universite de Sherbrooke | Pepin C.M.,Universite de Sherbrooke | Cadorette J.,Sherbrooke Molecular Imaging Center | Beaudoin J.-F.,Sherbrooke Molecular Imaging Center | And 7 more authors.
IEEE Nuclear Science Symposium Conference Record | Year: 2010

The scintillator is one of the key building blocks that critically determine the physical performance of PET detectors. The quest for scintillation crystals with improved characteristics has been crucial in designing scanners with superior imaging performance. Recently, it was shown that the decay time constant of high lutetium content Lu1.8Gd0.2SiO 5:Ce (LGSO) scintillators can be adjusted between 30 ns and 48 ns by varying the cerium concentration from 0.025 mol% to 0.75 mol%, thus providing interesting characteristics for phoswich detectors. The large light output (90-120% NaI), the better spectral match and the high initial photoelectron rate (200 phe+/ns) of these scintillators with avalanche photodiode (APD) readout promise to provide superior energy and timing resolution. Moreover, their improved mechanical properties as compared to conventional LGSO (Lu 0.2Gd1.8SiO5:Ce) make block array manufacturing readily feasible. To verify these assumptions, new phoswich block arrays made of LGSO-90%Lu with low and high mol% Ce concentrations were fabricated and assembled into LabPET modules. Typical crystal decay time constants were 32 ns and 48 ns, respectively. We therefore report on the initial evaluation of this modified version of the LabPET detector module. Phoswich crystal identification performed using a non-optimized digital pulse shape discrimination algorithm yielded an average 10% error. At 511 keV, energy resolution of 20 2% and 15 1% were obtained, while coincidence timing resolution between 4.9 0.3 ns and 4.1 0.1 ns were achieved. The improved characteristics of this new LGSO-based phoswich detector module are expected to enhance the LabPET scanner performance, first by improving sensitivity due to the overall higher stopping power of the detector module, and second by narrowing the coincidence time window, thus minimizing the random event rate. Altogether these two improvements will significantly enhance the noise equivalent count rate performance of an all LGSO-based LabPET scanner. © 2010 IEEE. Source

Shimizu S.,Universite de Sherbrooke | Shimizu S.,Applied Materials | Pepin C.M.,Universite de Sherbrooke | Pepin C.M.,Applied Materials | And 2 more authors.
IEEE Transactions on Nuclear Science | Year: 2010

Since its discovery in 1993, LGSO has been seen as a promising scintillator for positron emission tomography (PET) imaging. Recently, new high lutetium content Lu1.8 Gd0.2 SiO5 :Ce (LGSO-90%Lu) has been produced with Ce concentration varying from 0.025 to 0.75 mol% Ce, yielding decay times in the range of 34.2 to 44.8 ns. These scintillators could potentially be used as phoswich detectors in PET for improving spatial resolution. To validate this assumption, light output, energy resolution, temperature dependence, timing resolution, and pulse-shape discrimination performance were assessed. The light output of these LGSO scintillators is 3.5 to 4.8 times higher than BGO with avalanche photodiode readout [7.5 to 8 times with photomultiplier tube (PMT)] and increases with Ce concentration. The variation of light output for temperature ranging from 10 to 50 °C is less than 18% with PMT readout. Energy resolution at 662 keV is about 11% (l0%) with avalanche photodiode (APD) (PMT) readout. Timing resolution with APD is ∼1.65 ns for all samples relative to a fast PMT-plastic detector. Pulse-shape discrimination of LGSO-90% Lu with 0.025 mol% Ce (τ = 34.2 ns) and 0.75 mol% Ce (τ = 44.8 ns) was successfully achieved in a phoswich assembly, making this new high lutetium content LGSO with adjustable decay time constants a strong candidate for a high-resolution depth-of-interaction detector intended for PET imaging. © 2010 IEEE. Source

Shimizu S.,Universite de Sherbrooke | Shimizu S.,Applied Materials | Pepin C.M.,Universite de Sherbrooke | Pepin C.M.,Sherbrooke Molecular Imaging Center | And 2 more authors.
IEEE Transactions on Nuclear Science | Year: 2010

Fusion of functional PET or SPECT images and anatomical X-ray CT images would ideally be performed using data recorded concurrently with the same detection system under all three modalities to avoid inaccurate co-registration due to patient movements and normal physiological processes like respiratory motion. One possible approach to achieve this goal is to use an avalanche photodiode (APD) based scintillation detection system. Requirements on scintillators for such an application are high density and high timing resolution for PET, good energy resolution for SPECT, large light output and fast scintillation decay time for counting mode X-ray CT. The purpose of this work is to investigate new Lu1.8LgGdo.2SiO5:Ce (LGSO) scintillators with improved performance developed purposely for PET applications, but having suitable characteristics for SPECT and CT detection. LGSO with 90% Lu content has high density (7.3 g/cc), large light output (90-120% of NaI), good energy resolution (∼10-12% @ 511 keV), and fast decay time that can be adjusted from 34 to 45 ns by varying Ce concentration. In this work, LGSO with 0.025, 0.15 and 0.75 mol% Ce was assessed with APD readout for PET/SPECT/CT applications by measuring energy spectra at 511 keV (PET), 140 keV (SPECT) and 60 keV (CT), and timing resolution in reference to a fast plastic scintillator. LGSO-APD detectors can be considered as promising candidates for combined multimodality imaging scanners.. Source

Paquette M.,Sherbrooke Molecular Imaging Center | Phoenix S.,Sherbrooke Molecular Imaging Center | Ouellet R.,Sherbrooke Molecular Imaging Center | Langlois R.,Sherbrooke Molecular Imaging Center | And 4 more authors.
Molecular Imaging and Biology | Year: 2013

Purpose: The aim of this study was to compare the in vivo stability, uptake, and positron emission tomography (PET) imaging performance of a novel estrogen receptor PET tracer, 4-fluoro-11β-methoxy-16α-[ 18F]fluoroestradiol (4FMFES), with 16α-[18F] fluoroestradiol (FES). Procedures: MC7-L1 and MC4-L2 (ER+) cell lines and their ERα-knockdown variants (ERαKD) were implanted subcutaneously in Balb/c mice. After 21 days, mice were imaged using either FES or 4FMFES. One hour post-injection, static images were acquired for 30 min and the tumor %ID/g uptake values were derived. Biodistribution data were also obtained 1 h following the injection of either FES or 4FMFES. Blood samples were taken at different times and analyzed on thin-layer chromatography to quantify the presence of radiometabolites for each radiotracer. To assess specific targeting to the estrogen receptors, mice bearing only ER+ tumors were treated with the competitive ER inhibitor fulvestrant 48 h prior to imaging with 4FMFES. Results: Metabolic stability was found to be similar for both tracers in mice. Both FES and 4FMFES differentiated ER+ tumors from ERαKD tumors in biodistribution and PET imaging studies. 4FMFES achieved a significantly higher %ID/g uptake in ER+ tumors and MC4-L2 ERαKD tumors than FES in the PET imaging studies. Also, tumor-to-background ratio was higher in ER+ tumors using 4FMFES compared to FES. Dissection data showed a significantly higher %ID/g in all tested cell lines and ER-rich tissues using 4FMFES versus FES. Fulvestrant-treated mice had either low or undetectable tumor uptake. Conclusion: In a tumor-bearing mouse model, 4FMFES achieves better specific tumor uptake and better contrast than FES, making it a promising candidate for ER imaging. © 2013 World Molecular Imaging Society. Source

Nugent S.,Universite de Sherbrooke | Croteau E.,Universite de Sherbrooke | Croteau E.,Sherbrooke Molecular Imaging Center | Pifferi F.,Universite de Sherbrooke | And 6 more authors.
Prostaglandins Leukotrienes and Essential Fatty Acids | Year: 2011

Cerebral metabolic rate of glucose (CMRg) is lower in individuals affected by cognitive decline and dementia, especially in Alzheimer's disease. However, as yet there is no consensus as to whether CMRg decreases during healthy aging. Epidemiological studies show that weekly consumption of fish abundant in ω3 fatty acids has a protective effect on cognition during aging. Thus, the primary objective of this human study was to use positron emission tomography analysis with 18F-fluorodeoxyglucose to evaluate whether supplementation with a fish oil rich in ω3 fatty acids increases cerebral glucose metabolism in young or elderly adults. Healthy young (23±5y old; n=5) and elderly (76±3y old; n=6) women and men were included in the study. Semi-quantitative expression of the data as 'standardized uptake values' showed that elderly participants had significantly lower cerebral glucose metabolism compared with the young group. However, when expressed quantitatively a CMRg, there was no effect of age or ω3 supplementation on glucose metabolism in any of the brains regions studied. Higher plasma triglyceride levels and higher plasma insulin levels were associated with lower CMRg in several regions, suggesting that a trend towards the metabolic syndrome may be associated with cerebral hypometabolism. We conclude that under these experimental conditions, ω3 supplementation did not affect brain glucose metabolism in the healthy elderly. Future studies in this area should address whether glucose intolerance or other conditions linked to the metabolic syndrome impact negatively on brain glucose metabolism and cognition. © 2011 Elsevier Ltd. Source

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