title: Stroke assessment with diffusional kurtosis imaging.
abstract: OBJECTIVE
  Despite being the gold standard technique for stroke assessment, conventional diffusion MRI provides only partial information about tissue microstructure. Diffusional kurtosis imaging is an advanced diffusion MRI method that yields, in addition to conventional diffusion information, the diffusional kurtosis, which may help improve characterization of tissue microstructure. In particular, this additional information permits the description of white matter (WM) in terms of WM-specific diffusion metrics. The goal of this study is to elucidate possible biophysical mechanisms underlying ischemia using these new WM metrics.
  
  
  METHODS
  We performed a retrospective review of clinical and diffusional kurtosis imaging data of 44 patients with acute/subacute ischemic stroke. Patients with a history of brain neoplasm or intracranial hemorrhages were excluded from this study. Region of interest analysis was performed to measure percent change of diffusion metrics in ischemic WM lesions compared with the contralateral hemisphere.
  
  
  RESULTS
  Kurtosis maps exhibit distinct ischemic lesion heterogeneity that is not apparent on apparent diffusion coefficient maps. Kurtosis metrics also have significantly higher absolute percent change than complementary conventional diffusion metrics. Our WM metrics reveal an increase in axonal density and a larger decrease in the intra-axonal (Da) compared with extra-axonal diffusion microenvironment of the ischemic WM lesion.
  
  
  CONCLUSIONS
  The well-known decrease in the apparent diffusion coefficient of WM after ischemia is found to be mainly driven by a significant drop in the intra-axonal diffusion microenvironment. Our results suggest that ischemia preferentially alters intra-axonal environment, consistent with a proposed mechanism of focal enlargement of axons known as axonal swelling or beading.
authors.affiliation: Center for Biomedical Imaging, Department of Radiology and Radiological Science, Medical University of South Carolina, 68 President Street, MSC 120, Charleston, SC 29425, USA.
authors.forename: Edward S
authors.initials: ES
authors.lastname: Hui
authors.forename: Els
authors.initials: E
authors.lastname: Fieremans
authors.forename: Jens H
authors.initials: JH
authors.lastname: Jensen
authors.forename: Ali
authors.initials: A
authors.lastname: Tabesh
authors.forename: Wuwei
authors.initials: W
authors.lastname: Feng
authors.forename: Leonardo
authors.initials: L
authors.lastname: Bonilha
authors.forename: Maria V
authors.initials: MV
authors.lastname: Spampinato
authors.forename: Robert
authors.initials: R
authors.lastname: Adams
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Helpern
mesh_terms: D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D010865:Pilot Projects; D012189:Retrospective Studies; D020521:Stroke / Q000175:diagnosis*