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 Doav in postnatal brain development. MATERIALS AND METHODS Multisection maps of T1, T2, and the trace of the diffusion tensor (Trace[D] = 3 x Doav) were obtained in four kittens at eight time points. RESULTS In the adult, Doav was about 700 micron 2/sec in both white and gray matter. In the newborn, Doav was 1,100-1,350 micron 2/sec in white matter and 1,000 micron 2/sec in gray matter. For all anatomic regions and time points, the correlation between Doav and 1/T2 was high (R2 = 0.87, P << .001). T1 showed a lower correlation with Doav and a higher sensitivity to myelinization than did T2. CONCLUSION Although Doav shows dramatic changes in the maturing brain, the high correlation between Doav and T2 indicates that little additional information can be obtained by measuring this diffusion parameter during normal brain development. This contrasts with previous findings in brain ischemia, where Doav 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 Doav reduction in brain maturation and ischemia are different. Doav 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 Doav during ischemia, are probably of secondary importance.