title: Selecting the best index for following the temporal evolution of apparent diffusion coefficient and diffusion anisotropy after hypoxic-ischemic white matter injury in neonates.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Applied Physics, Eindhoven University of Technology, Eindhoven, The Netherlands. c.vanpul@mmc.nl
authors.forename: Carola
authors.initials: C
authors.lastname: van Pul
authors.forename: Jan
authors.initials: J
authors.lastname: Buijs
authors.forename: Maurice J A
authors.initials: MJ
authors.lastname: Janssen
authors.forename: George F
authors.initials: GF
authors.lastname: Roos
authors.forename: Marinus T
authors.initials: MT
authors.lastname: Vlaardingerbroek
authors.forename: Pieter F F
authors.initials: PF
authors.lastname: Wijn
mesh_terms: D000328:Adult; D016880:Anisotropy; D002545:Brain Ischemia / Q000175:diagnosis*; D016022:Case-Control Studies; D003198:Computer Simulation; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D000860:Hypoxia / Q000175:diagnosis*; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D013997:Time Factors