Cortical imaging as seen at ultrahigh field MRI

Abstract

Multiple Sclerosis (MS) has long been considered as White matter (WM) disease. The last decade, the significance of cortical lesions (CL) and their contribution to MS pathology has been intensely investigated. They have been shown to play a major role in physical and cognitive impairment in MS patients. CL detection has proven to be challenging, mainly due to poor contrast between cortical lesion and surrounding normal grey matter (GM) tissue. Various magnetic resonance imaging (MRI) sequences have been used to improve cortical lesion detection in MS patients. In recent years, Double inversion recovery (DIR), Phase sensitive inversion recovery (PSIR) and 7 Tesla T2* have been found to improve CL detection. Magnetization Transfer Imaging (MTI) has the advantage over conventional imaging as it reflects tissue myelin content. In this thesis, I present our studies using MTI at 7 Tesla to study cortical pathology in MS. 1) For a pilot study aiming to validate the use of magnetization transfer ratio (MTR) to detect cortical lesions, We examined the sensitivity of MTR to detect cortical lesions in comparison with 3 T DIR, 7 T PSIR, and 7 T T2* in 18 MS patients and 9 healthy controls. 2) A further 42 patients (11 clinically isolated syndrome (CIS), 11 relapsing remitting MS (RRMS), 10 primary progressive MS (PPMS), and 10 secondary progressive MS (SPMS)) and 8 healthy controls were scanned at baseline, 23 of these patients had a follow up scan at 12 months. MTR at 7 Tesla has increased sensitivity to detect cortical lesions compared to 3T DIR, 7T PSIR and 7T T2*. CL myelin content as measured by the mean MTR lesional values were the lowest in SPMS patients in comparison with the rest of MS phenotypes. CL mean MTR values, more than volume was associated with the degree of physical and cognitive disability in MS patients. When MTR was studied in a longitudinal study, we have seen more changes in average MTR of cortical lesions in SPMS and CIS patients compared to RRMS and PPMS patients