Correlation of diffusion tensor and dynamic perfusion MR imaging metrics in normal appearing corpus callosum: Support for primary hypoperfusion in multiple sclerosis

BACKGROUND AND PURPOSE: Hypoperfusion of the normal-appearing white matter in multiple scle-rosis (MS) may be related to ischemia or secondary to hypometabolism from wallerian degeneration (WD). This study evaluated whether correlating perfusion and diffusion tensor imaging (DTI) metrics in normal-appearing corpus callosum could provide support for an ischemic mechanism for hypoperfusion. MATERIALS AND METHODS: Fourteen patients with relapsing-remitting MS (RRMS) and 17 control subjects underwent perfusion MR imaging and DTI. Absolute measures of cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) were calculated. Mean diffusivity (MD) and fractional anisotropy (FA) maps were computed from DTI data. After visual coregistration of perfusion and DTI images, regions of interest were placed in the genu, central body, and splenium of normal-appearing corpus callosum. Pearson product-moment correlation coefficients were calculated using mean DTI and perfusion measures in each region. RESULTS: In the RRMS group, CBF and CBV were significantly correlated with MD in the splenium (r 0.83 and r 0.63, respectively; both P .001) and in the central body (r 0.86 and r 0.65, respectively; both P .001), but not in the genu (r 0.23 and 0.25, respectively; both P i