Abstract
BackgroundAccurate attenuation correction (AC) is one of the most important issues to be addressed in quantitative brain PET/MRI imaging. Atlas-based MRI AC (AB-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 cerebral blood flow (CBF) using H215O-PET/MRI was compared between the two MRAC methods, AB and ZTE.MethodTwelve patients with cerebrovascular disease (4 males, 43.2 ± 11.7 years) underwent H215O-PET/MRI studies with a 3-min PET scan 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 2 of them were followed up after several months interval. A total of 25 PET images were reconstructed as dynamic data using 2 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 AB- and ZTE-MRAC were then compared for global and regional differences.ResultsThe mean differences of IDIF curves at each point obtained from AB- and ZTE-MRAC dynamic data were less than 5%, and the differences in time-activity curves were very small. The means of CBF from AB- and ZTE-MRAC reconstructions calculated using each IDIF showed differences of less than 5% for all cortical regions. CBF images from AB-MRAC tended to show greater values in the parietal region and smaller values in the skull base region.ConclusionThe CBF images from AB- and ZTE-MRAC reconstruction showed no significant differences in regional values, although the parietal region tended to show greater values in AB-MRAC reconstruction. Quantitative values in the skull base region were very close, and almost the same IDIFs were obtained.
Highlights
A new hybrid scanner combining positron emission tomography (PET) and MRI, the PET/MRI system, should be very beneficial in the neuropsychiatric field, especially for the precise fusion of high-grade anatomical MR images and PET molecular imaging [1]
Estimation errors were small, especially in the phase of lower radioactivity, indicating that only small differences may be expected in the area under the curve of image-derived input function (IDIF) from the AB- and zero echo time (ZTE)-MR-based attenuation correction (MRAC) PET images
As the result of this small difference in IDIF curves, the cerebral blood flow (CBF) images calculated from Atlas-based MRI AC (AB-MRAC) reconstruction and those from ZTE-MRAC were very close, and the regional values were almost the same (Fig. 4)
Summary
A new hybrid scanner combining positron emission tomography (PET) and MRI, the PET/MRI system, should be very beneficial in the neuropsychiatric field, especially for the precise fusion of high-grade anatomical MR images and PET molecular imaging [1]. A multicenter study showed that these newer MRAC methods produced better and more reliable quantitative images than those from the simple Dixon-based method [8]. These recent studies suggested that the MRAC method has been improved in terms of quantitative PET evaluation using PET/MRI scanners. The IDIF method in H215O PET/MRI is useful and practical to estimate the arterial input function directly from the cerebral arteries [13], and the CBF values using IDIF were consistent with previous 15O-PET studies [14, 15]. The difference in quantitative measurements of cerebral blood flow (CBF) using H215O-PET/MRI was compared between the two MRAC methods, AB and ZTE. The CBF images from AB- and ZTE-MRAC were compared for global and regional differences
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