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The North American Imaging in Multiple Sclerosis Cooperative steering committee developed a uniform high-resolution 3T MR imaging protocol relevant to the quantification of cerebral lesions and atrophy and implemented it at 7 sites across the United States. They assessed intersite variability in scan data, by imaging a volunteer with relapsing-remitting MS with a scan-rescan at each site. In multicenter studies with consistent scanner field strength and manufacturer after protocol harmonization, systematic differences can lead to severe biases in volumetric analyses.

The authors performed consecutive pseudocontinuous arterial spin-labeling and phase-contrast MR imaging on 82 individuals (healthy young adults, healthy older adults, and older adults with cerebral small vessel disease or chronic stroke infarcts) and examined associations between extracranial phase-contrast hemodynamics and intracranial arterial spin-labeling characteristics, which were defined by labeling efficiency, temporal signal-to-noise ratio, and spatial coefficient of variation. Large-artery blood velocity was inversely associated with labeling efficiency, temporal SNR, and spatial coefficient of variation of arterial spin-labeling. They conclude that choosing arterial spin-labeling timing parameters with on-line knowledge of blood velocity may improve CBF quantification.