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Comparative MR Imaging Study of Brain Maturation in Kittens with T1, T2, and the Trace of the Diffusion Tensor

¹ Neuroimaging Branch, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bldg 10, Rm 4N252, 10 Center Dr, Bethesda, MD 20892-2289.

View larger version (85K): [in a new window]   Figure 1. Changes in brain tissues during development as depicted on the maps of T1 (top), the long component of T2 (middle), and Trace(D) (bottom). Anatomically corresponding coronal sections acquired in the same representative kitten and in an adult cat are shown. Five relevant time points have been selected. The time courses of Trace(D) and T2 show clear similarities. In both cases, the highest values are observed in the newborn brain, where WM appears brighter than GM. During development, Trace(D) and T2 decrease in a parallel manner with a progressive reduction of the WM-to-GM contrast. In the adult brain, both Trace(D) and T2 have similar values in WM and GM. The time course of T1 partly resembles that of T2 and Trace(D) for the first 5 weeks, but, after the 5th week, there is a clearly visible inversion in the contrast between WM (arrows) and GM.

View larger version (26K): [in a new window]   Figure 2a. Graphs show the time course of changes in mean values measured in four kittens for (a) the long component of T2, (b) T1, and (c) Trace(D) for ROIs in subcortical WM (), the internal capsule (), the corpus callosum (), the cortex (•), and the caudate nucleus (). Error bars = SDs, ms = milliseconds, s = seconds. The time course of the changes shown in a and c are similar for all ROIs. The changes shown in b show two patterns for WM and GM ROIs.

View larger version (28K): [in a new window]   Figure 2b. Graphs show the time course of changes in mean values measured in four kittens for (a) the long component of T2, (b) T1, and (c) Trace(D) for ROIs in subcortical WM (), the internal capsule (), the corpus callosum (), the cortex (•), and the caudate nucleus (). Error bars = SDs, ms = milliseconds, s = seconds. The time course of the changes shown in a and c are similar for all ROIs. The changes shown in b show two patterns for WM and GM ROIs.

View larger version (29K): [in a new window]   Figure 2c. Graphs show the time course of changes in mean values measured in four kittens for (a) the long component of T2, (b) T1, and (c) Trace(D) for ROIs in subcortical WM (), the internal capsule (), the corpus callosum (), the cortex (•), and the caudate nucleus (). Error bars = SDs, ms = milliseconds, s = seconds. The time course of the changes shown in a and c are similar for all ROIs. The changes shown in b show two patterns for WM and GM ROIs.

View larger version (22K): [in a new window]   Figure 3a. Scatterplots illustrate the correlations between (a) Trace(D) and 1/T1, (b) Trace(D) and 1/T2, and (c) 1/T2 and 1/T1. ms = milliseconds, s = seconds. Each scatterplot contains data from ROIs in subcortical WM (), the internal capsule (), the corpus callosum (), the cortex (•), and the caudate nucleus () in all animals at all time points. Significant degrees of correlation were found for all the correlations. Trace(D) and 1/T2 (b) are highly correlated, indicating that in all brain regions and at all time points these two parameters respond similarly to the various physicochemical and histologic changes that occur during tissue maturation. Relevant differences between the slope and the intercept of the regression lines for WM and GM ROIs were found between Trace(D) and 1/T1 (a) and 1/T1 and 1/T2 (c), reflecting a higher sensitivity of T1 to myelin.

View larger version (21K): [in a new window]   Figure 3b. Scatterplots illustrate the correlations between (a) Trace(D) and 1/T1, (b) Trace(D) and 1/T2, and (c) 1/T2 and 1/T1. ms = milliseconds, s = seconds. Each scatterplot contains data from ROIs in subcortical WM (), the internal capsule (), the corpus callosum (), the cortex (•), and the caudate nucleus () in all animals at all time points. Significant degrees of correlation were found for all the correlations. Trace(D) and 1/T2 (b) are highly correlated, indicating that in all brain regions and at all time points these two parameters respond similarly to the various physicochemical and histologic changes that occur during tissue maturation. Relevant differences between the slope and the intercept of the regression lines for WM and GM ROIs were found between Trace(D) and 1/T1 (a) and 1/T1 and 1/T2 (c), reflecting a higher sensitivity of T1 to myelin.

View larger version (19K): [in a new window]   Figure 3c. Scatterplots illustrate the correlations between (a) Trace(D) and 1/T1, (b) Trace(D) and 1/T2, and (c) 1/T2 and 1/T1. ms = milliseconds, s = seconds. Each scatterplot contains data from ROIs in subcortical WM (), the internal capsule (), the corpus callosum (), the cortex (•), and the caudate nucleus () in all animals at all time points. Significant degrees of correlation were found for all the correlations. Trace(D) and 1/T2 (b) are highly correlated, indicating that in all brain regions and at all time points these two parameters respond similarly to the various physicochemical and histologic changes that occur during tissue maturation. Relevant differences between the slope and the intercept of the regression lines for WM and GM ROIs were found between Trace(D) and 1/T1 (a) and 1/T1 and 1/T2 (c), reflecting a higher sensitivity of T1 to myelin.

View larger version (74K): [in a new window]   Figure 4. Late phase of myelinization in the internal capsule. Top: On T2-weighted MR images (5,000/100), the internal capsule (arrows) shows a progressive reduction in signal intensity as compared with GM structures such as the head of the caudate nucleus (*). Bottom: On maps of the long component of T2, there are minimal differences between the internal capsule and GM at all time points, which indicates that the contrast changes visible on T2-weighted images (top) are unrelated to changes in the long component of T2. This finding implies that for the evaluation of the later phase of myelinization in children, MR images acquired with a long repetition time and a relative short echo time (eg, 30 msec) would provide the same tissue contrast as do images acquired with a long echo time; the former would, however, have the advantage of a better signal-to-noise ratio.