R2’ is reduced in normal appearing white matter and lesions, and increased in the basal ganglia in patients with multiple sclerosis

Results R2’ was significantly reduced in MS lesions as compared to the normal appearing white matter (8.20 x 10 -3 s -1 vs 9.77 x 10 -3 s -1 , P<0.001). R2’ was also significantly lower in the NAWM in patients with MS as compared to healthy control patients (9.77 x 10 -3 s -1 vs 10.13 x 10 -3 s -1 P=0.01). Increases in R2’ were seen in the lenticular nucleus in patients with multiple sclerosis (14.57 x 10 -3 s -1 vs 13.42 x 10 -3 s -1 , P<0.001) and in the caudate nuclei (12.53 x 10 -3 s -1 vs 10.53 x 10 -3 s -1 , P<0.001) Discussion Increase in R2’ within the caudate and lenticular nucleus may represent abnormal iron deposition which is recognised pathologically in patients with multiple sclerosis. As the contribution of deoxyhaemaglobin to R2’ is proportional to the product of oxygen extraction fraction and deoxygenated blood volume, R2’ reduction within lesions and normal appearing white matter may suggest a reduction in oxygen extraction fraction. However this finding could also represent a reduction in deoxygenated blood volume, or reduction in non haeme iron, possibly due to loss of iron containing oligodendrocytes due to ongoing demyelination. Future studies should investigate changes in R2’ over time in acute lesions, or use modelling as proposed by other investigators to provide separate measures of oxygen extraction fraction and deoxygenated blood volume from R2’ 1 .