Although conventional MRI acquisitions are of essence in the monitoring of MS, they show low specificity towards the microstructural nature of tissue alterations and exhibit rather low correlations with clinical metrics (“clinico-radiological paradox”). Conversely, recent advances in brain relaxometry allow characterizing microstructural alterations on a single-subject basis; the question yet remains whether such quantitative measurements can help bridging the gap between radiological and clinical findings.
This study investigates whether automatically assessed alterations of T1 relaxation times in brain lesions and normal-appearing white matter (NAWM) improve clinico–radiological correlations in early MS with respect to conventional measures.
102 healthy controls (65% female, [21-59] y/o) and 50 early-MS patients (76% female, [19-52] y/o) underwent MRI at 3T (MAGNETOM Skyra, Siemens Healthcare, Erlangen, Germany). The employed 3D protocol comprised MPRAGE, FLAIR (both used for lesion segmentation as in [Fartaria et al., 2017, MICCAI]), and MP2RAGE for T1 mapping.
After the healthy controls’ data were spatially normalized into a study-specific template, reference T1 values in healthy tissues were established by linear, voxel-wise modelling of the T1 inter-subject variability [Piredda et al., MRM, 2020]. In the MS cohort, T1 deviations from the established references were calculated as z-score maps.
Correlations between the EDSS and conventional measures, i.e. lesion volume and count, were compared against correlations with z-score-derived metrics in lesions and NAWM, namely the volume of voxels exceeding a given z-score threshold.
Correlations between EDSS and lesion volume and count were found to be 0.23 and 0.18, respectively. Higher correlations were found between EDSS and the volume of voxels exceeding an absolute z-score threshold of 2, both in lesions and NAWM, with ρ=0.3 and ρ=0.33, respectively. Correlation further improved when considering only negative z-scores, ρ=0.36 for lesions and ρ=0.39 for NAWM. The highest correlation was found when considering absolute z-scores in the occipital lobe NAWM, ρ=0.47.
Microstructural alterations identified as T1 z-scores were found to improve clinico–radiological correlation in comparison to conventional measures (lesion volume and count). Of notice, negative z-scores (i.e. abnormal T1 shortening), which may be due to an increase in iron content, appear to be a potential predictor for the clinical state of an early MS patient.