Diffusion tensor imaging (DTI) is a new type of magnetic resonance imaging (MRI) that allows non-invasive mapping of the diffusion properties of brain water and reveals unique tissue property ‘diffusion anisotropy’.^1–5 MRI can measure the extent of water diffusion along an arbitrary axis. From this measurement, it is often found that the water tends to diffuse along a preferential axis, which has been shown to coincide with the orientation of the ordered structures. Based on the diffusion orientation of water molecules, the DTI technique can provide several imaging contrasts such as anisotropy maps and orientation maps or a combination of the two, called a color-coded orientation map or simply colormap hereafter. In the colormap, the brightness shows the extent of the anisotropy and the color represents fiber orientation. It is known that the tensor-based data processing is only an approximation of the underlying tissue properties and more sophisticated and time-consuming data acquisition and processing schemes have been postulated.^6–8 However, for developmental brains we believe that the tensor approximation is an available and accepted method to characterize the gross white matter architectures and microstructures. Scanning time is best used to enhance the image resolution rather than to perform the complicated data acquisition. The contrast from diffusion tensor MRI has been used to provide unique information about axonal tracts of human brain white matter.^1,9–13

It is especially useful for delineating the anatomy of premature brain that is not myelinated, and for which relaxation-based contrast is inadequate.^14–22 The technique can detect injuries in specific white matter tracts as well as demonstrate the rearrangement of tracts.^23–27 As DTI becomes widely available in clinical scanners, it is likely that DTI will be an important diagnostic tool for premature infants in the future.

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