Investigation of apparent diffusion coefficient and diffusion tensor anisotrophy in acute and chronic multiple sclerosis lesions

Abstract

Background and purpose: The various stages of multiple sclerosis (MS) are characterized by de- and remyelination as well as by inflammation. Diffusion MR imaging is sensitive to tissue water motion, which might correspond to these pathologic processes. Our purpose was to demonstrate differences in apparent diffusion coefficient (ADC) and diffusion tensor anisotropy in acute and chronic MS plaques and in normal-appearing brain.

Methods: Twelve MS patients underwent conventional and full-tensor diffusion MR imaging with B = 1221 s/mm2. Derivation of trace ADC and calculation of anisotropic scalars, including eccentricity, relative anisotropy (RA), and fractional anisotropy (FA) was performed on a per-pixel basis. Regions of interest of plaques and normal structures were determined on coregistered maps. MS lesions were classified as acute, subacute, or chronic on the basis of their appearance on conventional images and in relation to clinical findings.

Results: Seven patients had acute plaques with a concentric arrangement of alternating high and low signal intensity on diffusion-weighted images. In nine acute lesions, plaque centers had high ADC with reduced anisotropy compared with rim, normal-appearing white matter (NAWM), and chronic lesions. The thin rim of diffusion-weighted hyperintensity surrounding the center showed variable ADC and anisotropic values, which were not statistically different from NAWM. Subacute and chronic MS lesions had intermediate ADC elevations/anisotropic reductions. Calculated FA pixel maps were superior to eccentricity or RA maps; however, quality was limited by signal-to-noise constraints.

Conclusion: ADC and diffusion anisotropic scalars reflect biophysical changes in the underlying pathology of the demyelinating process.

fig 1.

Patient H.U.: 22-year-old woman with acute plaques and multiple neurologic signs and symptoms of 2 to 4 weeks' chronicity at first presentation of MS. A–F, Multiple monophasic ring lesions are identified on T1-weighted contrast-enhanced (A) and FLAIR (B) images. Lesion centers show hypointensity on diffusion-weighted image (C) with corresponding increased diffusibility (brightness) on calculated ADC map (D), caused by increased water mobility in regions of acute inflammation. Reduction in anisotropy in these regions is present on calculated maps of eccentricity (E) and FA (F). Note that region of peripheral edema is readily differentiated from thin plaque rim on ADC map. ADC values: NAWM, 0.00081; left periventricular acute plaque center, 0.00211; left periventricular acute plaque rim, 0.00124. FA values: NAWM, 0.299; left periventricular acute plaque center, 0.111; left periventricular acute plaque rim, 0.162.

fig 2.

Patient V.Y: 24-year-old man with 7-month history of relapsing-remitting MS presented with quadriparesis, most severe in upper extremities, and left periventricular acute plaque. A–E, Note delineation of the hyperintense rim on diffusion-weighted image and relative hypointensity of lesion center (A). T2-weighted echo-planar image shows marked central hyperintensity and slightly lower signal in rim (B). Center has increased diffusibility, appearing almost as bright as CSF, and has a low ADC value (dark) in the rim on calculated ADC map (C). FA (D) and eccentricity (E) maps reveal intermediate anisotropic values in rims relative to lesion centers, which approach isotropy. ADC values: NAWM, 0.00071; left periventricular acute plaque center, 0.00136; left periventricular acute plaque rim, 0.00066. FA values: NAWM, 0.430; left periventricular acute plaque center, 0.135; left periventricular acute plaque rim, 0.362.

fig 3.

Patient N.O.: 15-year-old girl with 10-month history of Schilder's MS variant. A–E, Unusual bihemispheric callosal plaque shows a mixed pattern with rim enhancement on T1-weighted contrast-enhanced (A) and T2-weighted (B) images. Diffusion-weighted image shows moderate hyperintensity, caused by T2 shine through in lesion center, with hyperintense rim (C). Calculated ADC map (not shown) revealed increased diffusibility in lesion center with slight decrease in rim. Calculated maps of FA (D) and eccentricity (E) show marked tendency toward isotropy in lesion center, with minimal anisotropic reduction in rim. ADC values: NAWM, 0.00068; acute plaque center, 0.00155; acute plaque rim, 0.00072. FA values: NAWM, 0.568; acute plaque center, 0.176; acute plaque rim, 0.312.

fig 4.

Patient B.O.: 53-year-old woman with 40-year history of MS, presenting with dementia. T2 hyperintensity and ADC elevation are apparent with loss of white matter anisotropy in multiple chronic periventricular and subcortical plaques. A–E, Diffusion-weighted image (A), T2-weighted echo-planar image (B), ADC map (C), and calculated maps of eccentricity (D) and FA (E). ADC values: NAWM, 0.00097; right corona radiata chronic plaque, 0.00083; left periventricular chronic plaque, 0.00071. FA values: NAWM, 0.334; right corona radiata chronic plaque, 0.289; left periventricular chronic plaque, 0.445.

fig 5.

A, ADC median and range of MS plaques as compared with deep gray matter (thalamus) and NAWM. B, FA median and range of MS plaques as compared with deep gray matter (thalamus) and NAWM.