Multiparametric qMTI Assessment and Monitoring of Normal Appearing White Matter and Classified T1 Hypointense Lesions in Relapsing-Remitting Multiple Sclerosis

Abstract

BackgroundQuantitative magnetization transfer imaging (qMTI)1 is an efficient technique that is sensitive to the density of the macromolecular protons which are found mainly in white matter myelin. ObjectiveThe aim of this study is to investigate the statistical significance of complementary qMTI parameters including magnetization transfer rate (Ksat)2 and longitudinal relaxation time under MT saturation pulse (T1sat)3 compared to magnetization transfer ratio (MTR)4 and longitudinal relaxation time (T1)5 in relapsing remitting multiple sclerosis (RRMS)6 patients. MethodsIn this study, conventional MRI protocols as well as MT-3DSPGR imaging were performed on twelve clinically definite RRMS patients and twelve age-matched controls. Two general methodologies were utilized for qMTI calculations, including global volumetric measurement of MTI-T1 parameters using a pixel-based analysis method throughout the brain white matter and the regional assessments within classified MS lesions with respect to their hypointensities on T1-weighted scans. MTI-T1 parameters of segmented lesions and normal appearing white matter (NAWM)7 in RRMS patients were evaluated in comparison with normal white matter (NWM)8 of control subjects. ResultsSignificant reductions of MTR and Ksat values in isointense (p<0.0001), mild (p<0.0001) and severe hypointense lesions in comparison with NAWM on T1-weighted scans, were associated with considerable increases in both tissue relaxation times with and without MT pulse, T1sat (p<0.0001) and T1 (p<0.0001) respectively. Similar significant changes of quantitative MT imaging parameters and T1 values were also seen in non-lesion areas of NAWM in MS patients compared to those of NWM in healthy volunteers. ConclusionComplementary qMT imaging parameter contributes to the magnetization transfer phenomenon including Ksat and T1sat can provide more reliable information about the magnitudes and mechanisms of myelin destruction in multiple sclerosis compared to the conventional MTR and T1 relaxation time values.