title: Changes in T2 relaxation time after stroke reflect clearing processes.
abstract: OBJECTIVE
  CT and MR imaging techniques are frequently used for the diagnosis and progress monitoring of ischemic stroke in clinical practice and research. After stroke, both methods are characterized by a transient pseudo-normalized imaging signal, the so-called fogging phenomenon. This study evaluates potential pathophysiological changes associated with fogging, as well as its influence on the correct determination of the ischemic lesion in a rat stroke model.
  
  
  METHODS
  Male spontaneously hypertensive rats were subjected to permanent middle cerebral artery occlusion. Ischemic lesion volume, brain edema and gray scale value spread within the ischemic lesion were determined on T2-weighted MR sequences at days 1, 4, 8, 11 and 29 after stroke onset, and compared with immunohistochemistry for astrogliosis, microglia/macrophage infiltration and angiogenesis.
  
  
  RESULTS
  All animals showed MR fogging at days 4, 8 and 11 after stroke. The transient normalization of T2 signals occurred independently from the development of infarct volumes, but coincided well with the spatio-temporal occurrence of necrosis, angiogenesis and microglia/macrophage infiltration.
  
  
  CONCLUSIONS
  Our results suggest that the fogging effect reflects the clearance of necrotic tissue within the ischemic lesion and is thus not relevant for the determination of the lesion volume.
authors.affiliation: Fraunhofer Institute for Cell Therapy and Immunology, Leipzig, Germany. daniel-christoph.wagner@izi.fraunhofer.de
authors.forename: Daniel-Christoph
authors.initials: DC
authors.lastname: Wagner
authors.forename: Alexander
authors.initials: A
authors.lastname: Deten
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Härtig
authors.forename: Johannes
authors.initials: J
authors.lastname: Boltze
authors.forename: Alexander
authors.initials: A
authors.lastname: Kranz
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D020244:Infarction, Middle Cerebral Artery / Q000150:complications / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D051381:Rats; D011918:Rats, Inbred SHR; D020521:Stroke / Q000209:etiology / Q000473:pathology*