Objective: Changes in signal intensity on T1- and T2-weighted MR images consistent with myelination in the corpus callosum occur during months 3-9 of postnatal life and occur earlier in the splenium than in the genu. We hypothesized that the rate of change in diffusion-tensor imaging parameters in the first year of life would be greater in the splenium, especially during months 3-9.
Subjects and methods: Fifty-two infants (age range, 0-52 weeks) underwent one MRI examination with a six-direction diffusion-tensor imaging sequence. Fractional anisotropy, apparent diffusion coefficient, radial diffusivity, and axial diffusivity were measured in the genu and splenium of the corpus callosum. For each parameter, the slopes of change in the splenium and in the genu were measured for the entire first year of life and for the age period 3-9 months. The ratios of slope of change in the splenium to that in the genu in these two periods were compared.
Results: For fractional anisotropy, the ratio of slope of change in the splenium to that in the genu was 1.67 in the first year and 4.00 for 3-9 months; apparent diffusion coefficient, 2.00 in the first year and 4.33 for 3-9 months; radial diffusivity, 1.75 in the first year and 4.40 for 3-9 months; and axial diffusivity, 3.25 in the first year and 4.86 for 3-9 months.
Conclusion: Rates of change were always greater in the splenium. For the age period 3-9 months, the splenium-to-genu ratio was approximately 1.5- to 2.5-fold as high as that for the entire year. These findings correspond well with the sequence of signal intensity changes in the corpus callosum.