American Journal of Neuroradiology 26:469-481, March 2005
© 2005 American Society of Neuroradiology
PEDIATRICS
Selecting the Best Index for Following the Temporal Evolution of Apparent Diffusion Coefficient and Diffusion Anisotropy After Hypoxic-Ischemic White Matter Injury in Neonates
a Department of Applied Physics, Eindhoven University of Technology, Eindhoven, The Netherlands
b the Department of Neonatology, Maxima Medical Center, Location Veldhoven, The Netherlands
c Department of Radiology, Maxima Medical Center, Location Veldhoven, The Netherlands
d Department of Clinical Physics, Maxima Medical Center, Location Veldhoven, The Netherlands
e the Department of Biomedical Engineering ORL, University Hospital Maastricht, The Netherlands
Address correspondence to Carola van Pul, PhD, Máxima Medical Center, Veldhoven, Department of Clinical Physics, P.O. Box 7777, 5500 MB Veldhoven; e-mail: c.vanpul{at}mmc.nl
BACKGROUND AND PURPOSE: Diffusion-weighted (DW) MR imaging is a useful technique for detecting ischemia. In adults and neonates, however, temporal changes on DW images after ischemia complicate interpretation. Our purpose was to investigate the temporal evolution of the apparent diffusion coefficient (ADC), diffusion-tensor (DT) imaging components, and anisotropy in neonatal brain after hypoxic-ischemic white matter injury and to determine which anisotropy index is preferable.
METHODS: DT images were obtained with single-shot echo-planar imaging, by using pulsed field gradients in six directions. Sixteen volunteers and 10 term neonates with normal MR images were evaluated to obtain reference values. Among the anisotropy indexes of fractional anisotropy (FA), relative anisotropy (RA), volume ratio (VR), linear (CI) and planar (Cp) diffusion, and axial anisotropy (Am), simulations were performed to select the most appropriate indexes for clinical practice. The ADC, DT imaging components, and anisotropy were evaluated as a function of time after onset of symptoms in 11 neonates with hypoxic ischemia.
RESULTS: In neonates, changes in lesions were characterized by a large decrease (40%) in all eigenvalues, with a stronger decrease in the direction perpendicular to the fibers, resulting in increased anisotropy indexes. The temporal evolution of the relative change in ADC did not show a significant trend (P > .05). The relative change in anisotropy decreased linearly with time (P < .05), with the strongest trend in anisotropy index Am.
CONCLUSION: In clinical practice, anisotropy indexes FA, RA and Am appear to be useful. Am is the best index to monitor anisotropy changes. DT imaging provides information about diffusion parallel and perpendicular to white matter fibers, which helps the interpretation of physiologic changes after hypoxic-ischemic injury.
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