Fast and reliable quantitative measures of white matter development with magnetic resonance fingerprinting.

Developmental cognitive neuroscience aims to shed light on evolving relationshipsbetween brain structure and cognitive development. To this end, quantitativemethods that reliably measure individual differences in brain tissue propertiesare fundamental. Standard qualitative MRI sequences are influenced by scanparameters and hardware-related biases, and also lack physical units, making theanalysis of individual differences problematic. In contrast, quantitative MRIcan measure physical properties of the tissue but with the cost of long scandurations and sensitivity to motion. This poses a critical limitation forstudying young children. Here, we examine the reliability of an efficientquantitative multiparameter mapping method-magnetic resonancefingerprinting (MRF)-in children scanned longitudinally. We focus on T1values in white matter, since quantitative T1 values are known to primarilyreflect myelin content, a key factor in brain development. Forty-nine childrenaged 8-13 years (mean 10.3 years ± 1.4) completed 2 scanningsessions 2-4 months apart. In each session, two 2-min 3D-MRF scans at 1mm isotropic resolution were collected to evaluate the effect of scan durationon image quality and scan-rescan reliability. A separate calibration scanwas used to measure B0 inhomogeneity and correct for bias. We examined theimpact of scan time and B0 inhomogeneity correction on scan-rescanreliability of values in white matter, by comparing single 2-min and combinedtwo 2-min scans, with and without B0 correction. Whole-brain voxel-basedreliability analysis showed that combining two 2-min MRF scans improvedreliability (Pearson's r = 0.87) compared with a single 2-min scan(r = 0.84), while B0 correction had no effect on reliability in whitematter (r = 0.86 and 0.83 4- vs. 2-min). Using diffusion tractography, wesegmented major white matter fiber tracts and examined the profiles ofMRF-derived T1 values along each tract. We found that T1 values from MRF showedsimilar or greater reliability compared with diffusion parameters. Lastly, wefound that R1 (1/T1) values in multiple white matter tracts were significantlycorrelated with age. In sum, MRF-derived T1 values were highly reliable in alongitudinal sample of children and replicated known age effects. Reliability inwhite matter was improved by longer scan duration but was not affected by B0correction, making it a quick and straightforward scan to collect. We proposethat MRF provides a promising avenue for acquiring quantitative brain metrics inchildren and patient populations where scan time and motion are of particularconcern.