SNc and LC volumetry based on NM-MRI resulting from the automated segmentation and quantification technique can yield high diagnostic accuracy for differentiating PD from health and might be an unbiased disease biomarker. © 2015 International Parkinson and Movement Disorder Society.

Arterial Spin Labeling (ASL) can be implemented by combining different labeling schemes and readout sequences. In this study, the performance of 2D and 3D single-shot pulsed-continuous ASL (pCASL) sequences was assessed in a group of young healthy volunteers undergoing a baseline perfusion and a functional study with a sensory-motor activation paradigm. The evaluated sequences were 2D echo-planar imaging (2D EPI), 3D single-shot fast spin echo with in-plane spiral readout (3D FSE spiral), and 3D single-shot gradient-and-spin-echo (3D GRASE). The 3D sequences were implemented with and without the addition of an optimized background suppression (BS) scheme. Labeling efficiency, signal-to-noise ratio (SNR), and gray matter (GM) to white matter (WM) contrast ratio were assessed in baseline perfusion measurements. 3D acquisitions without BS yielded 2-fold increments in spatial SNR, but no change in temporal SNR. The addition of BS to the 3D sequences yielded a 3-fold temporal SNR increase compared to the unsuppressed sequences. 2D EPI provided better GM-to-WM contrast ratio than the 3D sequences. The analysis of functional data at the subject level showed a 3-fold increase in statistical power for the BS 3D sequences, although the improvement was attenuated at the group level. 3D without BS did not increase the maximum t-values, however, it yielded larger activation clusters than 2D. These results demonstrate that BS 3D single-shot imaging sequences improve the performance of pCASL in baseline and activation studies, particularly for individual subject analyses where the improvement in temporal SNR translates into markedly enhanced power for task activation detection.

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Purpose To improve pseudo continuous arterial spin labeling (PCASL) robustness to off-resonance and pulsatile blood flow velocity. Methods The Bloch equations were solved to evaluate the effect of labeling parameters in a pulsatile flow model for a range of off-resonance. Experimental confirmation was achieved in volunteers using linear phase increase between labeling pulses to approximate off-resonance errors. The location of the labeling plane was first assessed on four volunteers, then a range of parameters, including balanced and unbalanced gradients, were explored in five more volunteers at an optimal labeling plane location. Results Simulations demonstrated that high velocities are vulnerable to off-resonance, that unbalanced PCASL outperforms balanced PCASL, that increased B1 and low average gradient improve the labeling efficiency for high velocity flow, and a low ratio of selective to average gradient improves off-resonance robustness. A good agreement between theory and experiment was observed. Conclusion The robustness of PCASL can be increased by selecting an unbalanced scheme with a low average gradient (0.5mT/m), a low ratio (7x) of selective to average gradients and the highest feasible B1 (1.8uT). Placing the labeling plane above the carotid bifurcation and below the V3 segment, usually between the second and third vertebrae, produces robust results.

We compared three implementations of single-shot arterial spin labeled (ASL) perfusion magnetic resonance imaging (MRI): two-dimensional (2D) pulsed ASL (PASL), 2D pseudo-continuous ASL (PCASL), and background suppressed (BS) 3D PCASL obtained in a cohort of patients with mild cognitive impairment (MCI) and elderly controls. Study subjects also underwent 18F-flurodeoxyglucose positron emission tomography (18F-FDG PET). While BS 3D PCASL showed the lowest (p<0.001) gray matter-white matter cerebral blood flow (CBF) contrast ratio, it provided the highest (p<0.001) temporal signal-to-noise ratio. Mean relative CBF estimated using the PCASL methods in posterior cingulate cortex (PCC), precuneus and hippocampus showed hypoperfusion in the MCI cohort compared to the controls consistent with hypometabolism measured by 18F-FDG PET. BS 3D PCASL demonstrated the highest discrimination between controls and patients with effect size comparable to that seen with 18F-FDG PET. 2D PASL did not demonstrate group differentiation with relative CBF in any ROI, whereas 2D PCASL demonstrated significant differences only in PCC and hippocampus. Mean global CBF values did not differ across methods and were highly correlated, however the correlations were significantly higher (p<0.001) when either the same labeling (PCASL) or the same acquisition strategy (2D) was used as compared to when both the labeling and readout methods differed. In addition, there were differences in regional distribution of CBF between the three modalities, which can be attributed to differences in sequence parameters. These results demonstrate the superiority of ASL with PCASL as well as BS 3D readout as a biomarker for regional brain function changes in MCI.