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 orientat ionally averaged water diffusion coefficient D-oav in postnatal brain devel opment. MATERIALS AND METHODS: Multisection maps of T1, T2, and the trace of the di ffusion tensor (Trace[D] = 3 x D-oav) were obtained in four kittens at eigh t time points. RESULTS: In the adult, D-oav was about 700 mu m(2)/sec in both white and gr ay matter. In the newborn, D-oav was 1,100-1,350 mu m(2)/sec in white matte r and 1,000 mu m(2)/sec in gray matter. For ail anatomic regions and time p oints, the correlation between D-oav and 1/T2 was high (R-2 = 0.87, P << .0 01). T1 showed a lower correlation with D-oav and a higher sensitivity to m yelinization than did T2. CONCLUSION: Although D-oav shows dramatic changes in the maturing brain, th e high correlation between D-oav and T2 indicates that tittle additional in formation can be obtained by measuring this diffusion parameter during norm al brain development. This contrasts with previous findings in brain ischem ia, where D-oav and T2 appear to be uncorrelated. After including the autho rs' data and published iontophoretic measurements in a simple model of diff usion in tissues, the authors suggest that the underlying mechanisms of D-o av 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.