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Monte Carlo analysis of scattered radiation in time-of-flight positron emission tomography
| Title: | Monte Carlo analysis of scattered radiation in time-of-flight positron emission tomography |
| Author: | Muzic, Raymond Frank, Jr. |
| Description: | Positron Emission Tomography is a functionally based medical imaging modality that utilizes coincidence detection of collinear annihilation photons to reconstruct a quantitative image of the in vivo radiotracer distribution. The presence of scattered coincidences, caused by deflection of one or both of the detected annihilation photons, manifests itself as a degradation in image quality and quantitative accuracy, thus compromising the diagnostic value of the image. The purpose of this thesis is to characterize the magnitude and spatial distribution of scattered radiation so that, in the future, a scheme may be developed to correct images for scatter. To accomplish this goal, a Monte Carlo simulation that models radiation transport through the object and PET camera was developed. The simulation is based on MCNP, a mature, general purpose Monte Carlo code, with customization for needs specific to time-of-flight PET. Strong evidence of the simulation accuracy was found in the good agreement between measured and simulated data. Data obtained from simulation studies of the SP3000 indicate that scattered coincidences are rejected primarily due to geometrical factors related to the camera design and not by energy discrimination. It was also found that, for objects as large a s a human head, the spatial distribution of scattered coincidences in a reconstructed image (obtained without correction for attenuation) is less spatially variant than the point spread function of the PET camera. Further, the distribution is peaked and centered at the source position indicating scattered coincidences contain much good information about the source geometry. A preliminary application of variance reduction resulted in improved Monte Carlo simulation efficiency and indicates that variance reduction merits further investigation. These findings demonstrate the power of Monte Carlo simulation for studying scattered radiation in PET. In the future, the simulation will be used to investigate the use of radiotracers that emit cascade photons in addition to annihilation photons, to study the impact of increased time-of-flight resolution, to examine the contribution of scattered coincidences to attentuation scans, to calculate the probability necessary for maximum likelihood reconstructions, and to determine a scheme for eliminating scattered coincidences from images. |
| Permanent Link: |
http://rave.ohiolink.edu/etdc/view?acc_num=case1056039087
http://hdl.handle.net/2374.OX/16091 |
| Date: | 1991 |
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