PAPER

Mechanisms of normal appearing corpus callosum injury related to pericallosal T1 lesions in multiple sclerosis using directional diffusion tensor and ¹H MRS imaging

J Oh¹, R G Henry¹, C Genain², S J Nelson¹, D Pelletier²

¹ Magnetic Resonance Science Center, Department of Radiology, University of California, San Francisco, CA, USA
² UCSF Multiple Sclerosis Center, Department of Neurology, University of California, San Francisco, CA, USA

Correspondence to:
Correspondence to:
Dr J Oh
Magnetic Resonance Science Center, Department of Radiology, Box 0946, University of California, San Francisco, 185 Berry St, Suite 350, San Francisco, CA 94107, USA; joonmi{at}mrsc.ucsf.edu

Objectives: To investigate the extent of tissue damage in a region of normal appearing corpus callosum (NACC) for different forms of multiple sclerosis (MS) using diffusion tensor and proton magnetic resonance (MR) spectroscopic imaging.

Methods: A total of 47 patients with MS and 15 controls were included. Regions of interest from the NACC were manually segmented using high resolution anatomical images. Diffusion tensor eigenvalues and metabolite ratio of N-acetyl-aspartate (NAA) to creatine/phosphocreatine (Cr) were calculated in the NACC region.

Results: Increased apparent diffusion coefficients (ADCs) and decreased anisotropy were observed in the NACC for patients with MS relative to the control subjects. These resulted from increased diffusion tensor eigenvalues perpendicular to the maximum diffusion direction. The NAA:Cr ratio was decreased in the NACC for patients with MS relative to the control subjects. Significant correlations between pericallosal T1 lesion load and MR modalities in the NACC were observed for patients with relapsing remitting/secondary progressive MS (RR/SPMS), but not for patients with primary progressive MS (PPMS).

Conclusion: This study provides further insight into changes in the ADC and diffusion anisotropy based on the diffusion tensor eigenvalues for patients with MS. The changes in the diffusion tensor eigenvalues and NAA:Cr ratio in the NACC for patients with RR/SPMS suggest axonal injury and/or dysfunction induced by wallerian degeneration. The lack of correlation between these variables in the NACC and focal MS lesions for patients with PPMS further supports intrinsic differences related to tissue injury between these subtypes of MS.

Abbreviations: ADC, apparent diffusion coefficient; 3D SPGR, three dimensional spoiled gradient echo; CSF, cerebrospinal fluid; Cr, creatine/phosphocreatine; EDSS, Expanded Disability Status Scale; FLAIR, fluid attenuated inversion recovery; ¹H MRSI, proton magnetic resonance spectroscopic imaging; MS, multiple sclerosis; NAA, N-acetyl-aspartate; NAWM, normal appearing white matter; PPMS, primary progressive MS; SPMS, secondary progressive MS; ROI, region of interest; RRMS, relapsing remitting MS

Keywords: diffusion tensor eigenvalues; 1H MRSI; corpus callosum; wallerian degeneration; multiple sclerosis

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