Evolution of multiple sclerosis lesions on serial contrast-enhanced T1-weighted and magnetization-transfer MR images

Abstract

Background and purpose: Magnetization-transfer imaging is a technique that could provide indirect evidence of the characteristics of multiple sclerosis (MS) lesions. The purpose of this work was to study the evolution of MS lesions on T1-weighted MR images over time and to investigate changes in magnetization-transfer ratio (MTR) values of MS lesions with different initial appearances on contrast-enhanced T1-weighted images.

Methods: Eleven patients with relapsing-remitting MS were studied with MR imaging. The MTRs were calculated for 47 lesions that had been classified according to their appearance on contrast-enhanced T1-weighted images. Each patient was examined at four time points over a 1-year period. The MTR changes observed in the selected lesions were compared with their initial T1-weighted appearance.

Results: The lowest MTR values were initially found in hypointense nonenhancing lesions and in ring-enhancing lesions, with both types showing a hypointense center. Changes in MTR values were more dynamic and reversible in ring-enhancing than in hypointense nonenhancing plaques. Nodular-enhancing lesions had slightly lower initial MTRs than did isointense non-enhancing lesions.

Conclusion: The absence or presence of contrast uptake may indicate a different pathologic basis for hypointense MS lesions on T1-weighted MR images. These differences should be kept in mind when considering T1 lesion load as a surrogate marker of disability in MS.

fig 1.

Two-dimensional plot of mean MTR values versus time (in months). MTR values are stratified according to the appearance of MS lesions on the baseline contrast-enhanced T1-weighted image. Hypointense nonenhancing, nodular-enhancing, and ring-enhancing lesions show a significant MTR increase on the 12-month image. The increase is higher for ring-enhancing lesions and occurs mainly during the first 3 months. MTR values in the NAWM and the isointense nonenhancing lesions do not show significant changes. Open circles indicate NAWM; triangles, isointense without enhancement; solid circles, nodular-type enhancement; squares, hypointense without enhancement; diamonds, ring-type enhancement.

fig 2.

A–C, T1 isointense nonenhancing lesion in the right frontal white matter. Axial T2-weighted image (2200/80/1) (A) and contrast-enhanced T1-weighted image (550/14/2) (B) at a comparable anatomic level are shown at day 0 and at 12 months (C). The lesion (arrow, A) shows no significant change on the 12-month image, and the MTR values remained between 35% on the baseline image and 33% on the 12-month image.

fig 3.

A–C, Serial MR follow-up of a ring-enhancing lesion in the left periventricular temporal white matter. The lesion (arrow, A) is shown at three time points: baseline (A), 1 month (B), and 12 months (C) on contrast-enhanced T1-weighted images (550/14/2). The ring-enhancing pattern at baseline disappears on the 1-month image. At 12 months, the lesion is completely isointense with respect to NAWM on contrast-enhanced T1-weighted images. In this lesion, the MTR increased from 22% on the baseline image to 36% after 12 months.

fig 4.

A and B, Serial MR follow-up of a nodular-enhancing lesion in the right frontal white matter and a nonenhancing hypointense lesion (arrow, A) in the left frontal white matter (arrowhead, A) on contrast-enhanced T1-weighted images (550/14) at baseline (A) and 12 months later (B). The nodular-enhancing lesion has become completely isointense on the 12-month image. In this lesion, the MTR increased from 34% on the baseline image to 39% on the 12-month image. The nonenhancing lesion in the left frontal lobe shows no significant change on the serial MR follow-up images, and the MTR values remained between 24% on the baseline image and 26% on the 12-month image.