Simulations using Monte-Carlo packages are increasingly used in Nuclear Imaging, both for PET and SPECT applications. Either for modeling imaging systems or developing algorithms for analysis and ...improvement of image quantification. The aim of this work is the study of several scatter phenomena and the evaluation and improvement of two scatter correction compensation methods in pixelized scintillators. Firstly, the Dual Energy Window Subtraction Technique (DEWST) and then the Multi Energy Window and Filtering Technique (MEWFT) are investigated. Minimization Method has been used in order to achieve the best weighting co-efficient and the appropriate position and width of each low energy window. The position of them was found to be around 80–120
keV. Following scatter rejection, both quality and quantitative accuracy of the images improved.
Myeloperoxidase (MPO) is an enzyme which is a member of the haem-peroxidase superfamily and plays a role in production of reactive oxygen species. The most common polymorphism in the promoter region ...of MPO gene is -463 G/A. It was shown that carrying the GG genotype means increased activity of the gene approximately 2-3-fold compared to GA and AA genotypes. It was found that hyperglycaemia, modified oxidized proteins and increased advanced glycosylated end products (AGE) are related to oxidative stress in diabetes. Under the hyperglycaemic conditions, production of reactive oxygen radical is elevated in smooth muscle endothelial cells, mesengial and tubular endothelial cells. Especially, elevated lipid oxidation plays an important role in pathogenesis of diabetic complications such as cardiovascular complications. We examined the MPO -463 G/A polymorphism by using the PCR-RFLP method in 145 type 2 diabetic patients and 151 healthy controls. We observed that the AA genotype and A allele were protective variants against type 2 diabetes and the GG genotype was a risk factor for diabetes. While we studied the relationship between genotypes and biochemical parameters, we found that patients with the A allele had decreased serum cholesterol, triglyceride, VLDL levels and body mass index. We suggest that the MPO gene has an important role in pathogenesis of type 2 diabetes because of the increased frequency of GG genotype, which is related to increased activity and oxidant capacity of MPO in the patients.
The purpose of this study is to assess the performance of iterative reconstruction methods, using phantom data from a prototype small-animal PET system. The algorithms compared are the simultaneous ...versions of ART (SART), EM-ML, ISRA WLS and a new iterative algorithm we have introduced under the short name ISWLS. The evaluation study was based on reconstructed image quality, as it is derived from visual inspection, cross-correlation coefficient and CNRs (contrast-to-noise ratios) of specific ROIs (region-of-interest). In general EM-ML and ISRA present similar reconstruction time and minor differences in reconstructed image quality. Slightly superior performances show WLS and SART while ISWLS improves reconstruction resolution at the edges of the field of view.
MRP approaches to PET image reconstruction Karali, E.; Koutsouris, D.
2011 4th International Conference on Biomedical Engineering and Informatics (BMEI),
2011-Oct., Letnik:
1
Conference Proceeding
The purpose of this study is to introduce a novel empirical iterative algorithm for medical image reconstruction, under the short name MRP-ISWLS (Median Root Prior Image Space Weighted Least ...Squares). We use phantom data from a prototype small-animal PET system and the methods presented here are applied to 2D sinograms. Further, we assess the performance of the new algorithm by comparing it to the simultaneous version of MRP-EM-ML (Median Root Prior Expectation Maximization Maximum Likelihood). Both algorithms are compared in terms of reconstruction time and CNRs (Contrast-to-Noise Ratios). As it turns out, MRP-ISWLS presents higher CNRs than MRP-EM-ML for objects of different size. Also MRP-ISWLS has better noise manipulation.
In this study, the thermoluminescence (TL) characteristics of Ag-doped and undoped lithium tetraborate (Li2 B4 O7 , LTB) materials, grown using the Czochralski method, were reported. The TL ...properties of LTB:Ag, such as glow curve structure, dose response, fading and reproducibility, were investigated. The glow curve of the Li2 B4 O7 :Ag single crystal consists of four peaks located at approximately 75, 130, 190 and 275°C; in undoped LTB, the single crystal shows a broad glow curve with peaks at 65, 90, 125, 160 and 190°C using a heating rate of 5°C/s in the 50-350°C temperature region. The high temperature peak of Ag-doped sample at 275°C has a nonlinear dose response within the range from 33 mGy to 9 Gy. There is a linear response in the range of 33-800 mGy; after which, a sublinear region appears up to 9 Gy for Ag-doped LTB single crystal. For undoped single crystal, the dose response is supralinear for low doses and linear for the region between 1 and 9 Gy. The thermal fading ratio of the undoped material is almost 60% for the high temperature peak after 7 days. Ag-doped LTB single crystal exhibits different behaviour over a period of 7 days.
SPECT images suffer from low contrast as a result of photons scatter. The standard method for excluding scatter component in pixelized scintillators is the application of an energy window around the ...central photopeak channel of each crystal cell, but small angle scattered photons still appear in the photopeak window and they are included in the reconstructed images. In this work we have assessed three subtraction techniques that use a different approach in order to calculate the scatter component and subtract it from the photopeak image. The dual energy window subtraction technique (DEWST) the convolution subtraction technique (CST) and a deconvolution technique (DT). All these techniques are compared to the standard method. The experimental results showed the superiority of DT, as a scatter correction technique.
Nucl.Instrum.Meth. A564 (2006) 597-607 The front-end electronics of the ATLAS hadronic calorimeter (Tile Cal) is
housed in a unit, called {\it PMT-Block}. The PMT-Block is a compact instrument
...comprising a light mixer, a PMT together with its divider and a {\it 3-in-1}
card, which provides shaping, amplification and integration for the signals.
This instrument needs to be qualified before being assembled on the detector. A
PMT-Block test bench has been developed for this purpose. This test bench is a
system which allows fast, albeit accurate enough, measurements of the main
properties of a complete PMT-Block. The system, both hardware and software, and
the protocol used for the PMT-Blocks characterisation are described in detail
in this report. The results obtained in the test of about 10000 PMT-Blocks
needed for the instrumentation of the ATLAS (LHC-CERN) hadronic Tile
Calorimeter are also reported.
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