The Assessment of Pathological Changes in the Classified T1 Hypointense Lesions and Normal Appearing White Matter of Relapsing-Remitting MS Patients using Quantitative Magnetization Transfer Imaging (qMTI)

摘要

Quantitative magnetization transfer imaging (qMTI) is a new technique that is sensitive to the density of the macromolecular protons which are found mainly in white matter myelin. The aim of this study is to investigate MT parameters changes, including magnetization transfer ratio (MTR), magnetization transfer rate (K{sub}(sat)) and native longitudinal relaxation times with and without applying MT saturation pulse (T1{sub}(sat) and T1{sub}(free)) in the brain tissue of normal individuals and multiple sclerosis (MS) patients. In this research, conventional MRI protocols such as T2-FSE, T1-SE, FLAIR sequences as well as MT-3DSPGR imaging were performed on twelve patients with clinically definite relapsing-remitting MS and twelve age-matched controls. An automated method was used to create white matter and lesion masks with both of high contrast T1-SPGR scans with a flip angle of 30° and clinical FLAIR images. White matter and MS lesion masks were superimposed on MT parametric maps. MTI parameters of segmented lesions and normal appearing with matter (NAWM) were evaluated in comparison with normal white matter of control subjects. Significant reductions of MTR and K{sub}(sat) in mildly and severely hypointense lesions on T1-weighted scans comparing with those lesions that are isointense to white matter, were associated with considerable increases in tissue longitudinal times, T1{sub}(sat) and T1{sub}(free) (p<0.0001). Similar significant changes of quantitative MT imaging parameters were also seen in MS patients' white matter compared to those of normal white matter in healthy volunteers. A strong correlation coefficient was found between K{sub}(sat) and T1{sub}(free) measurements in NAWM (r{sup}2=0.86, p<0.0001) whereas there was only a moderately good correlation between previous parameters in isointense lesions (r{sup}2=0.66, p<0.001). A similar acceptable correlation coefficient between MTR and K{sub}(sat) values were also reported in NAWM (r{sup}2=0.71, p<0.001). Significant changes of MT parameters in classified T1-hypointense lesions and NAWM, reflecting degrees of destruction in the myelin macromolecular structure. The significant changes of MTI parameters in NAWM and different types of MS abnormalities which are in various stages of the demyelinating process, in comparison with similar brain anatomical regions in normal subjects, can be considered as reliable estimates of disease burden than the conventional MRI methods.