Three chemical forms of atmospheric tritium, i.e., tritiated water vapor (HTO), hydrogen gas (HT), and hydrocarbons (CH3T), were measured at Kumamoto, Japan during the period between 2003 and 2005. The average concentrations were in the order of HT, CH3T, and HTO. The yearly average HT concentrations were not so different in each year, while that of CH3T showed a large variation. The concentrations of all chemical species have decreased compared to those measured during the period between 1984 and 1995 at Fukuoka, about 100 km north of the present sampling location, suggesting a decrease in emissions of HT and CH3T from their sources for these 8-10 years. The decrease in HTO concentration would be attributed to the decrease of the bomb-produced tritium and to a regional characteristic of the sampling locations; Kumamoto showed lower tritium concentrations in rain than Fukuoka.
LV volumes calculated with OS-EM and Astonish without attenuation and scatter corrections corresponded to the true obtained by the Update number about 32 times and 24 times when using the OS-EM and Astonish method with attenuation and scatter corrections, respectively. However, LV volumes have changed greatly in the Astonish method according to the change in the Update number. Appropriate numbers of iterations and subsets are the measurement of global LV volumes, especially when using the OS-EM algorithm with RC.
Purpose: We performed partial volume effect correction of PET images using 18 F-FDG-PET and CT images taken consecutively, compared it with correction using MRI images, and investigated the usefulness of correction using CT images. Methods: A total of 9 clinically normal subjects were included in the study, and the CT and MRI images of each subject were segmented and normalized. PET images were coregistered to each morphological image and then normalized. The normalized morphological images of each subject were used to mask the brain atlas and to correct for the partial volume effect. For each brain region, comparison of counts, two-group test between CT-and MRI-corrected groups, and correlation analysis were performed. Results: As a result of correction, some error was observed between the two groups. Correlation analysis showed strong positive correlations in many areas, but weak correlations were found in some areas. In the region where significant differences were found, the two groups showed strong positive correlation, and in the region where weak correlation was found, the error tended to be small. Conclusion: It is suggested that the correction by CT can be performed with the same accuracy, although some errors are generated compared with MRI.
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