Comparative MR imaging study of brain maturation in kittens with T1, T2, and the trace of the diffusion tensor

PURPOSE: To assess the time-course of the relaxation times and the orientationally averaged water diffusion coefficient D-oav in postnatal brain development. MATERIALS AND METHODS: Multisection maps of T1, T2, and the trace of the diffusion tensor (Trace[D] = 3 x D-oav) were obtained in four kittens at eight time points. RESULTS: In the adult, D-oav was about 700 mu m(2)/sec in both white and gray matter. In the newborn, D-oav was 1,100-1,350 mu m(2)/sec in white matter and 1,000 mu m(2)/sec in gray matter. For ail anatomic regions and time points, the correlation between D-oav and 1/T2 was high (R-2 = 0.87, P << .001). T1 showed a lower correlation with D-oav and a higher sensitivity to myelinization than did T2. CONCLUSION: Although D-oav shows dramatic changes in the maturing brain, the high correlation between D-oav and T2 indicates that tittle additional information can be obtained by measuring this diffusion parameter during normal brain development. This contrasts with previous findings in brain ischemia, where D-oav and T2 appear to be uncorrelated. After including the authors' data and published iontophoretic measurements in a simple model of diffusion in tissues, the authors suggest that the underlying mechanisms of D-oav reduction in brain maturation and ischemia are different. D-oav changes during development are mainly affected by events occurring in the cellular compartment, while changes in extracellular volume fraction and tortuosity, which are thought to determine the reduction in D-oav during ischemia, are probably of secondary importance.