Abstract
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Objectives: Accurate attenuation correction (AC) is one of the most important issues to be addressed in quantitative brain PET/MRI imaging. CT atlas (CTA) based MR attenuation correction (MRAC), one of the representative MRAC methods, has been used to estimate the skull attenuation in brain scans. The zero echo time (ZTE) pulse sequence is also expected to provide a better MRAC estimation in brain PET scans. The difference in quantitative measurements of CBF using H215O-PET/MRI was compared between the two MRAC methods, CTA and ZTE.
Methods: Twelve patients with cerebrovascular disease (4 males, 43.2±11.7y) underwent H215O-PET/MRI studies with a 3-min PET and MRI scans including the ZTE sequence. Eleven of them were also studied under the conditions of baseline and 10 min after acetazolamide administration, and two of them were followed up after several months interval. A total of 25 PET images were reconstructed as dynamic data using two sets of reconstruction parameters to obtain the image-derived input function (IDIF), the time-activity curves of the major cerebral artery extracted from images, and CBF images. The CBF images from CTA- and ZTE-MRAC were then compared for global and regional differences.
Results: The mean differences of IDIF curves at each point obtained from CTA- and ZTE-MRAC dynamic data were less than 5%, and the differences in time-activity curves were very small. The means of CBF from CTA- and ZTE-MRAC reconstructions calculated using each IDIF showed differences of less than 4% for all cortical regions. A scatter plot of the regional CBF values from the 310 ROIs used for regional CBF measurement showed a good correlation. CBF images from CTA-MRAC tended to show greater values in the parietal region and smaller values in the skull base region. Conclusion: The CBF images from CTA- and ZTE-MRAC reconstruction showed no significant differences in regional values, although the parietal region tended to show greater values in CTA-MRAC reconstruction. Quantitative values in the skull base region were very close, and almost the same IDIFs were obtained.