Cerebral Hemodynamics In Hypertension: Regional Cerebral Blood Flow Detection Using Three Dimensional Pseudo-Continuous Arterial Spin Labeling

PartⅠReliability of Three-Dimensional Pseudo-Continuous Arterial Spin Labeling MR Imaging for Measuring Visual Cortex Perfusion on Two 3T ScannersObjectives:Cerebral blood flow (CBF) in the human primary visual cortex is correlated with the loss of visual function in neuro-ophthalmological diseases. Advanced threedimensional pseudo-continuous arterial spin labeling (3D pCASL), as a non-invasive method to access the CBF, can be a novel measurement to detect the visual cortex. The objective of the study was to assess the intra- and inter-scanner reliability of 3D pCASL of the visual cortex in healthy adults and suggest the selection of different post-labeling delay times (PLDs).Method:3D pCASL was conducted in two 3.0T MR three times with twelve healthy volunteers at an interval of 13 days. The 1st and 3rd tests were performed on scanner-1, and the 2nd test was performed on scanner-2. The value of the CBF was abstracted from the visual cortex with two PLDs. The intra- and inter-scanner reliability and reproducibility were evaluated with the intraclass correlation coefficient (ICC) and Bland-Altman plot.Results:By estimating the mean value of the CBF in the visual cortex, the intra-scanner results demonstrated the higher reliability (ICC for PLD=1.5 second presented at 0.743 compared with 0.829 for PLD=2.5 seconds), and the Bland-Altman plot showed the reproducibility at a longer PLD.Conclusion:We conclude that the calibrated 3D pCASL approach provides a highly reproducible measurement of the CBF of the visual cortex that can serve as a useful quantitative probe for research conducted at multiple centers and for the long-term observation of the clinical effects of neuro-opthalmological diseases.Part IIReduced Visual Cortex Perfusion without Volume Loss in Mild to Moderate HypertensionObjectives:Visual cortex pathology in hypertension is associated with progressive long-term ocular disability. Detection of visual cortex abnormalities in mild to moderate hypertension may therefore be valuable in understanding and predicting the ocular long-term course. However, structural MRI measures such as volume measurement have only shown abnormalities without the region of visual cortex in hypertension. We therefore investigated for evidence of abnormality in visual cortex perfusion, consistent with metabolic dysfunction and the volume measurement, in mild to moderate hypertension.Methods:27 mild to moderate hypertensive patients without ocular impairment and 32 age-matched healthy controls underwent 3 Tesla MRI with a three dimensional pseudo-continuous arterial spin labelling sequence and a volumetric T1-weighted sequence to quantify visual cortex perfusion and volume separately. Voxel-based morphometric analysis and region of interest method were used to compare regional visual cortex perfusion and volume separately. Independent t test was performed to compare the inter-group difference in the significance of modifications in CBF and volume.Results:Compared with control group, hypertensive group exhibited reduced CBF values in the binocular cortex including the brodmann17,18 and 19(P<0.05) without evident statistical volume significance.Conclusions:The decreased visual cortex perfusion without volume loss is consistent with cerebrovascular metabolic dysfunction in mild to moderate hypertension without evident ocular target organ diseases. We suspect there is a variety of the hemodynamics prior to the change of the morphology in the visual cortex in hypertension. However, larger cohorts and longitudinal follow-up studies are imperative to investigate the functional and prognostic significance of the early visual cortex perfusion deficits.Part IIIChanges of Cerebral Hemodynamics in Mild to Moderate Hypertension:Regional Cerebral Blood Flow Measurement Using Quantitative Arterial Spin LabelingObjectives:The purpose of this study was to assess the value of threedimensional pseudo-continuous arterial spin labeling (3D pCASL) perfusion MRI in hypertension. We evaluated abnormal regional cerebral blood flow (CBF) in the whole brain and investigated the underlying cerebrovascular mechanism regarding secondary cerebral complications stems from hypertension.Method:CBF values were acquired using a 3D pCASL sequence on 63 subjects, including a hypertensive group (n=30; male,17) and a control group (n=33; male,17). Data were analyzed with post-processing software to evaluate regional CBF. Scan-time blood pressure was measured using the in vivo magnitude 3150 pedestal monitor. Two-sampled t test was performed to compare the inter-group difference in regional CBF.Results:Compared with the control group, the hypertensive group exhibited reduced CBF values in the cerebellum, medulla, midbrain, pons, frontal lobe, temporal lobe, parietal and occipital lobe (P<0.05). Nevertheless, no statistically significant difference in the CBF values was observed in the basal ganglion region between the two groups.Conclusion:3D pCASL can be applied for the detection of regional CBF abnormalities in patients with hypertension. Moreover, the regionally specific decline in CBF may implicate underlying cerebrovascular complications.