title: Patterns of lesion development in multiple sclerosis: longitudinal observations with T1-weighted spin-echo and magnetization transfer MR.
abstract: OBJECTIVE
  We evaluated the appearance of enhancing multiple sclerosis (MS) lesions on unenhanced T1-weighted MR images and the natural course of enhancing MS lesions on serial unenhanced T1-weighted and magnetization transfer (MT) MR images.
  
  
  METHODS
  One hundred twenty-six enhancing lesions were followed up monthly for 6 to 12 months to determine their signal intensity on unenhanced T1-weighted and MT MR images. At the time of initial enhancement, the size of the lesion and the contrast ratio of enhancement were calculated for each enhancing lesion. During follow-up, the contrast ratio on the corresponding unenhanced T1-weighted image was measured, and an MT ratio (MTR) was calculated.
  
  
  RESULTS
  Twenty-five enhancing lesions (20%) appeared isointense and 101 lesions (80%) appeared hypointense relative to normal-appearing white matter on unenhanced T1-weighted images. During 6 months of follow-up, four MR patterns of active lesions were detected: initially isointense lesions remained isointense (15%); initially isointense lesions became hypointense (5%, most of which reenhanced); initially hypointense lesions became isointense (44%); and initially hypointense lesions remained hypointense (36%). MTR was significantly lower for hypointense lesions as compared with isointense lesions at the time of initial enhancement. For lesions that changed from hypointense to isointense, MTR increased significantly during 6 months of follow-up. Multiple regression analysis showed that strongly decreased MTR at the time of initial enhancement and enhancement duration of more than one scan were predictive of a hypointense appearance on unenhanced T1-weighted images at 6 months' follow-up. Ring enhancement was found to be the only (weak) predictor of persistently hypointense signal intensity.
  
  
  CONCLUSIONS
  Most enhancing lesions appear slightly to significantly hypointense on unenhanced T1-weighted images. Although most hypointensities are reversible, only those lesions that fail to recover on unenhanced T1-weighted and MT images may have considerable irreversible structural changes.
authors.affiliation: Department of Radiology, MR Center for MS Research, Academic Hospital Vrije Universiteit, Amsterdam, The Netherlands.
authors.forename: J H
authors.initials: JH
authors.lastname: van Waesberghe
authors.forename: M A
authors.initials: MA
authors.lastname: van Walderveen
authors.forename: J A
authors.initials: JA
authors.lastname: Castelijns
authors.forename: P
authors.initials: P
authors.lastname: Scheltens
authors.forename: G J
authors.initials: GJ
authors.lastname: Lycklama à Nijeholt
authors.forename: C H
authors.initials: CH
authors.lastname: Polman
authors.forename: F
authors.initials: F
authors.lastname: Barkhof
mesh_terms: D000293:Adolescent; D000328:Adult; D001921:Brain / Q000473:pathology*; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009103:Multiple Sclerosis / Q000145:classification / Q000473:pathology* / Q000503:physiopathology; D012008:Recurrence; D013997:Time Factors