title: Evolution of the diffusion-weighted signal and the apparent diffusion coefficient in the late phase after minor stroke: a follow-up study.
abstract: BACKGROUND
  Diffusion-weighted imaging (DWI) is mainly used in acute stroke, and signal evolution in the acute phase has been studied extensively. However, patients with a minor stroke frequently present late. Recent studies suggest that DWI may be helpful at this stage, but only very few published data exist on the evolution of the DW-signal in the weeks and months after a stroke. We performed a follow-up study of DWI in the late stages after a minor stroke.
  
  
  METHODS
  28 patients who presented 48 hours to 14 days after a minor stroke underwent serial MRI at baseline, 4 weeks, 8 weeks, 12 weeks, 6 months and>or=9 months after their event. Signal intensity within the lesion was determined on T2-weighted images, DW-images and the Apparent Diffusion Coefficient (ADC) map at each time-point, and ratios were calculated with contralateral normal values (T2r, DWIr, ADCr).
  
  
  RESULTS
  T2r was increased in all patients from the beginning, and showed no clear temporal evolution. ADCr normalized within 8 weeks in 83% of patients, but still continued to increase for up to 6 months after the event. The DW-signal decreased over time, but was still elevated in 6 patients after>or=6 months. The evolution of ADCr and DWIr showed statistically highly significant inter-individual variation (p<0.0001), which was not accounted for by age, sex, infarct size or infarct location.
  
  
  CONCLUSIONS
  The ADC and the DW-signal may continue to evolve for several months after a minor ischaemic stroke. Signal evolution is highly variable between individuals. Further studies are required to determine which factors influence the evolution of the ADC and the DW-signal.
authors.affiliation: Department of Clinical Stroke Prevention Research Unit, University of Neurology, Radcliffe Infirmary, and Centre for Clinical Magnetic Resonance Research, John Radcliffe Hospital, Oxford, OX2 6HE, United Kingdom.
authors.forename: U G R
authors.initials: UG
authors.lastname: Schulz
authors.forename: E
authors.initials: E
authors.lastname: Flossmann
authors.forename: J M
authors.initials: JM
authors.lastname: Francis
authors.forename: J N
authors.initials: JN
authors.lastname: Redgrave
authors.forename: P M
authors.initials: PM
authors.lastname: Rothwell
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001931:Brain Mapping; D038524:Diffusion Magnetic Resonance Imaging; D018450:Disease Progression; D017352:Echo-Planar Imaging; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008297:Male; D008875:Middle Aged; D020521:Stroke / Q000175:diagnosis*; D013997:Time Factors