DTI tracks brain abnormalities in babies

Diffusion tensor MR imaging, which depicts the displacement of water molecules through tissue, can visualize changes to ischemic brain white matter in infants at least two to three hours before conventional MRI can document changes, according to a study in the July issue of Radiology.

Because of the high incidence of severe motor problems in newborns with hypoxic-ischemic injury in the white matter, researchers sought to retrospectively investigate the feasibility of fiber tracking at birth and three months in this patient population.

Carola van Pul, Ph.D., and colleagues from Máxima Medical Center in Veldhoven, the Netherlands, studied seven normal infants and 10 infants with perinatal hypoxic ischemia. Imaging was performed on a 1T scanner (Gyroscan, Philips Medical Systems), and the protocol included the acquisition of T1-weighted spin-echo, T2-weighted fast spin-echo, and inversion-recovery images.

Neonatal patients were sedated with chloral hydrate and fixated by using a vacuum pillow. The imaging protocol also included diffusion tensor imaging, which was performed by using pulsed field gradients in six directions with single-shot echo-planar MRI.

The researchers applied fiber tracking to construct a 3D visualization of the brain's white matter tracts based on the diffusion tensor images. The procedure was repeated after three months to monitor the development of the injured regions. This is the first time a group of newborns has been evaluated with fiber tracking at birth and at three months, according to the study. The seven normal infants served as a reference group.

Color maps in the infant group with fiber abnormalities showed a disturbed fiber pattern compared with the reference group. The affected areas, showed increased anisotropy, which was apparent in both white matter areas and the gyri.

Typically, white matter damage results in decreased anisotropy, as the cellular matrix loses its ability to funnel water in a single direction. In this case and in other studies, researchers have observed an increase in anisotropy in lesions in newborns. The implications of these observations are not clear, according to the authors.

At birth, fiber tracking showed a different fiber pattern in eight of the 10 neonates with ischemia, compared with the images obtained from the normal infants. The fiber pattern of the brain's white matter was disturbed in several areas of the brain, including the corpus callosum and, most significantly, the corona radiata, which is associated with finely coordinated movement.

Six of the 10 infants continued to exhibit disturbed fiber patterns at follow-up. All of the infants who had disturbed patterns in the corona radiata at three months had major motor problems.

While the feasibility of fiber tracking has been demonstrated, the researchers cautioned that it is not yet validated in this population. Results should be carefully interpreted.

For more information from the Diagnostic Imaging archives:

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