Abstract
Until recently, no direct comparison between [15O]water positron emission tomography (PET) and arterial spin labeling (ASL) for measuring cerebral blood flow (CBF) was possible. With the introduction of integrated, hybrid magnetic resonance (MR)-PET scanners, such a comparison becomes feasible. This study presents results of CBF measurements recorded simultaneously with [15O]water and ASL. A 3T MR-BrainPET scanner was used for the simultaneous acquisition of pseudo-continuous ASL (pCASL) magnetic resonance imaging (MRI) and [15O]water PET. Quantitative CBF values were compared in 10 young healthy male volunteers at baseline conditions. A statistically significant (P<0.05) correlation was observed between the two modalities; the whole-brain CBF values determined with PET and pCASL were 43.3±6.1 mL and 51.9±7.1 mL per 100 g per minute, respectively. The gray/white matter (GM/WM) ratio of CBF was 3.0 for PET and 3.4 for pCASL. A paired t-test revealed differences in regional CBF between ASL and PET with higher ASL-CBF than PET-CBF values in cortical areas. Using an integrated, hybrid MR-PET a direct simultaneous comparison between ASL and [15O]water PET became possible for the first time so that temporal, physiologic, and functional variations were avoided. Regional and individual differences were found despite the overall similarity between ASL and PET, requiring further detailed investigations.
Highlights
Positron emission tomography (PET) with 15O-labeled water is considered to be the gold standard for quantifying cerebral blood flow (CBF).[1]
Averaged whole-brain CBF of the 10 subjects measured at baseline condition after sleep was 43.3±6.1 mL per 100 g per minute for positron emission tomography (PET) and 51.9±7.1 mL per 100 g per minute for arterial spin labeling (ASL)
Compared with PET, the averaged CBF in GM measured by ASL is higher (67.3±8.2 versus 51.8±7.7 mL per 100 g per minute) and the averaged CBF in WM is similar (19.5±5.8 versus 17.4±3.1 mL per 100 g per minute), which results in a gray/white matter (GM/WM) ratio of 3.4 and 3.0 for ASL and PET, respectively
Summary
Positron emission tomography (PET) with 15O-labeled water is considered to be the gold standard for quantifying cerebral blood flow (CBF).[1] because of the limited availability of PET in general, the need of an on-site cyclotron for the production of [15O]water, and the inherent radiation dose of the radiotracer, the MRI-based method of arterial spin labeling (ASL) has been recently considered as a viable alternative to determine CBF.[2,3]. By using radiofrequency (RF)-labeled arterial blood as an intrinsic tracer, ASL can noninvasively measure CBF. Low SNR is mainly because of the low fraction of blood within each voxel and T1 decay of the label.[4,5] To evaluate the reliability and reproducibility of ASL, several studies have compared ASL-MRI with [15O]water PET.[2,3,6,7,8] Novel ASL techniques such as pseudo-continuous ASL (pCASL) deployed at 3T9–11 have substantially contributed to the attainment of high SNR (SNR 1⁄4 13.8) CBF data. Remaining differences between ASL and PET were reported.[8,12]
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