Quantitative assessment of iron accumulation in the deep gray matter of multiple sclerosis by magnetic field correlation imaging

Abstract

Background and purpose: Deposition of iron has been recognized recently as an important factor of pathophysiologic change including neurodegenerative processes in multiple sclerosis (MS). We propose that there is an excess accumulation of iron in the deep gray matter in patients with MS that can be measured with a newly developed quantitative MR technique--magnetic field correlation (MFC) imaging.

Materials and methods: With a 3T MR system, we studied 17 patients with relapsing-remitting MS and 14 age-matched healthy control subjects. We acquired MFC imaging using an asymmetric single-shot echo-planar imaging sequence. Regions of interest were selected in both deep gray matter and white matter regions, and the mean MFC values were compared between patients and controls. We also correlated the MFC data with lesion load and neuropsychologic tests in the patients.

Results: MFC measured in the deep gray matter in patients with MS was significantly higher than that in the healthy controls (P < or = .03), with an average increase of 24% in the globus pallidus, 39.5% in the putamen, and 30.6% in the thalamus. The increased iron deposition measured with MFC in the deep gray matter in the patients correlated positively with the total number of MS lesions (thalamus: r = 0.61, P = .01; globus pallidus: r = 0.52, P = .02). A moderate but significant correlation between the MFC value in the deep gray matter and the neuropsychologic tests was also found.

Conclusion: Quantitative measurements of iron content with MFC demonstrate increased accumulation of iron in the deep gray matter in patients with MS, which may be associated with the disrupted iron outflow pathway by lesions. Such abnormal accumulation of iron may contribute to neuropsychologic impairment and have implications for neurodegenerative processes in MS.

Fig 1.

T2-weighted images (left) and MFC color maps (right) in a 29-year-old patient with MS (top row) and a 32-year-old control subject (bottom row). Note the clearly increased MFC in the deep gray matter regions on MFC maps (arrows) in the patient (B) relative to the control subject (D), though such a difference is not remarkable on conventional T2-weighted images (A, C).

Fig 2.

Graph showing significant correlation of MFC in the thalamus and number of lesions in patients with relapsing-remitting MS. This trend indicates the role of white matter lesions (with axonal transection) in the accumulation of iron in deep gray matter by interruption of iron transport from the deep gray matter nuclei to the cortical regions.