There is controversy concerning the discrepancy between absolute cerebral blood flow (CBF) values measured using positron emission tomography (PET) and magnetic resonance imaging (MRI). To gain insight into this problem, the increased signal-to-noise ratio (SNR) and extended T(1) relaxation times of blood and tissue at 3.0 T were exploited to perform pulsed arterial spin labeling (PASL) MRI measurements as a function of spatial resolution and post-labeling delay. The results indicate that, when using post-labeling delays shorter than 1500 ms, MRI gray matter flow values may become as high as several times the correct CBF values owing to tissue signal contamination by remaining arterial blood water label. For delays above 1500 ms, regional PASL-based CBF values (n = 5; frontal gray matter: 48.8 +/- 3.3(SD) ml/100 g/min; occipital gray matter: 49.3 +/- 4.5 ml/100 g/min) comparable with PET-based measurements can be obtained by using spatial resolutions comparable with PET (5-7.5 mm in-plane). At very high resolution (2.5 x 2.5 x 3 mm(3)), gray matter CBF values were found to increase by 10-20%, a consequence attributed to reduction in partial volume effects with cerebrospinal fluid and white matter. The recent availability of MRI field strengths of 3.0 T and higher will facilitate the use of MRI-based CBF measurements in the clinic.
"Perfusion is then calculated from the difference of labeled (tag) and non-labeled (control) images. Despite early concerns due to ASL's intrinsic low sensitivity, recent developments of labeling strategies (Wu et al., 2007; Dai et al., 2008) and acquisition methods (Fernández-Seara et al., 2005; Garcia et al., 2005) have considerably improved its reliability, with a high degree of agreement to PET (Xu et al., 2010; Donahue et al., 2006b) and DSC-MRI (Weber et al., 2003). "
"c o m / l o c a t e / y n i m g regional differences in the brain's physiological response to caffeine. We measured cerebral blood flow (CBF) which reflects a combined contribution of a direct effect of caffeine on cerebrovasculature and an indirect effect through potential modulations on neural activity and brain metabolism (Alsop et al., 2014; Donahue et al., 2006; Kety and Schmidt, 1948). We reason that, if a regional heterogeneity can be identified, it would indicate that either the direct vasoconstriction effect is region-dependent or that neural response to caffeine is different across brain regions. "
"CBF quantification was performed using the one-compartment model (Buxton 2005), and a mean CBF map was generated for each scan. Thirdly, a partial volume correction was applied to correct the CBF map for each voxel by the fraction of the gray and the white matter (Donahue et al. 2006). Finally, corrected CBF map of each subject was normalized to the standard Montreal Neurological Institute (MNI) template provided by SPM8 and smoothed using FWHM of 6 mm before group-level analysis. "
[Show abstract][Hide abstract] ABSTRACT: Short- and long-term effects of transjugular intrahepatic portosystemic shunt (TIPS) on cerebral blood flow (CBF) in patients with cirrhosis are still unclear. The purpose of this longitudinal study was to explore CBF alteration patterns in cirrhotic patients after TIPS. Thirteen cirrhotic patients (7 male, 6 female, mean age 50.0 ± 9.3 years) underwent arterial-spin labeling (ASL) MRI 1-9 days (median 1 days) before TIPS. Follow-up MR examinations were performed about 1 week (median 6 days), 3 months (n = 6), 6-9 months (n = 5) and 12-18 months (n = 5) after TIPS. CBF, ammonia level, Child-Pugh score, number connection test type A (NCT-A) and digit symbol test (DST) scores were converted into relative values by dividing by his/her pre-TIPS values, and then, compared via one-way analysis of variance (ANOVA). Correlations between the pre- and post-TIPS changes of relative CBF (rCBF) and the changes of relative ammonia (rAmmonia), Child-Pugh (rChild-Pugh), and NCT-A/DST (rNCT-A/rDST) scores were calculated by crossing subjects. Compared with the pre-TIPS level, the global rCBF slightly increased by 10.9 % about 1 week later, then rapidly decreased by 14.2 % 3 months later, and flatly decreased by 17.2 % in 6-9 months and 18.0 % in 12-18 months following TIPS. The changes of 3-month rDST score were slightly correlated with 3-month rCBF rather than 1-week rCBF, (P < 0.1, FDR-corrected) No difference was found between the pre- and post-TIPS rAmmonia levels, rChild-Pugh and rNCT-A/rDST scores (Post-hoc P > 0.05). CBF measured at different time points after TIPS insertion showed different patterns, indicating varying longitudinal effects of TIPS on CBF. A sharp decline of rCBF was found in the 1 week to 3 months period after insertion, indicating that high event rate of hepatic encephalopathy might relate with the unadaptable CBF in patients undergoing TIPS insertion.
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