title: Oscillating gradient diffusion MRI reveals unique microstructural information in normal and hypoxia-ischemia injured mouse brains.
abstract: OBJECTIVE
  We investigated whether oscillating gradient diffusion MRI (dMRI) can provide information on brain microstructural changes after formaldehyde fixation and after hypoxic-ischemic (HI) injury beyond that provided by conventional dMRI.
  
  
  METHODS
  Pulsed gradient spin echo (PGSE) and oscillating gradient spin echo (OGSE) dMRI of the adult mouse brain was performed in vivo (50-200 Hz, b = 600 mm(2)/s), and a similar protocol was applied to neonatal mouse brains at 24 h after unilateral hypoxia-ischemia. Animals were perfusion fixed with 4% paraformaldehyde for ex vivo dMRI and histology.
  
  
  RESULTS
  Apparent diffusion coefficients (ADCs) measured in the live adult mouse brain presented tissue-dependent frequency-dependence. In vivo OGSE-ADC maps at high oscillating frequencies (>100 Hz) showed clear contrast between the molecular layer and granule cell layer in the adult mouse cerebellum. Formaldehyde fixation significantly altered the temporal diffusion spectra in several brain regions. In neonatal mouse brains with HI injury, in vivo ADC measurements from edema regions showed diminished edema contrasts at 200 Hz compared with the PGSE results. Histology showed severe tissue swelling and necrosis in the edema regions.
  
  
  CONCLUSIONS
  The results demonstrate the unique ability of OGSE-dMRI in delineating tissue microstructures at different spatial scales.
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Dan
authors.initials: D
authors.lastname: Wu
authors.forename: Lee J
authors.initials: LJ
authors.lastname: Martin
authors.forename: Frances J
authors.initials: FJ
authors.lastname: Northington
authors.forename: Jiangyang
authors.initials: J
authors.lastname: Zhang
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002531:Cerebellum / Q000473:pathology*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D017352:Echo-Planar Imaging; D020925:Hypoxia-Ischemia, Brain / Q000473:pathology*; D007091:Image Processing, Computer-Assisted / Q000379:methods; D051379:Mice; D008810:Mice, Inbred C57BL; D009991:Oscillometry / Q000379:methods*
keywords: diffusion MRI; mouse brain; neonatal hypoxia-ischemia; oscillating gradient; tissue microstructure