title: Numerical simulation model of hyperacute/acute stage white matter infarction.
abstract: OBJECTIVE
  Although previous studies have revealed the mechanisms of changes in diffusivity (apparent diffusion coefficient [ADC]) in acute brain infarction, changes in diffusion anisotropy (fractional anisotropy [FA]) in white matter have not been examined. We hypothesized that membrane permeability as well as axonal swelling play important roles, and we therefore constructed a simulation model using random walk simulation to replicate the diffusion of water molecules.
  
  
  METHODS
  We implemented a numerical diffusion simulation model of normal and infarcted human brains using C++ language. We constructed this 2-pool model using simple tubes aligned in a single direction. Random walk simulation diffused water. Axon diameters and membrane permeability were then altered in step-wise fashion. To estimate the effects of axonal swelling, axon diameters were changed from 6 to 10 microm. Membrane permeability was altered from 0% to 40%. Finally, both elements were combined to explain increasing FA in the hyperacute stage of white matter infarction.
  
  
  RESULTS
  The simulation demonstrated that simple water shift into the intracellular space reduces ADC and increases FA, but not to the extent expected from actual human cases (ADC approximately 50%; FA approximately +20%). Similarly, membrane permeability alone was insufficient to explain this phenomenon. However, a combination of both factors successfully replicated changes in diffusivity indices.
  
  
  CONCLUSIONS
  Both axonal swelling and reduced membrane permeability appear important in explaining changes in ADC and FA based on eigenvalues in hyperacute-stage white matter infarction.
authors.affiliation: Center for Promotion of Excellence in Higher Education, Kyoto University, Kyoto, Japan. sakai@mbox.kudpc.kyoto-u.ac.jp
authors.forename: Koji
authors.initials: K
authors.lastname: Sakai
authors.forename: Kei
authors.initials: K
authors.lastname: Yamada
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Oouchi
authors.forename: Tsunehiko
authors.initials: T
authors.lastname: Nishimura
mesh_terms: D001369:Axons / Q000502:physiology / Q000648:ultrastructure; D020520:Brain Infarction / Q000503:physiopathology*; D002463:Cell Membrane Permeability; D003198:Computer Simulation; D006801:Humans; D008959:Models, Neurological; D009413:Nerve Fibers, Myelinated / Q000502:physiology / Q000648:ultrastructure; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water