title: Quantification of perfusion using bolus tracking magnetic resonance imaging in stroke: assumptions, limitations, and potential implications for clinical use.
abstract: BACKGROUND
  MR techniques have been very powerful in providing indicators of tissue perfusion, particularly in studies of cerebral ischemia. There is considerable interest in performing absolute perfusion measurements, with the aim of improving the characterization of tissue "at risk" of stroke. However, some important caveats relating to absolute measurements need to be taken into account. The purpose of this article is to discuss some of the issues involved and the potential implications for absolute cerebral blood flow measurements in clinical use.
  
  
  RESULTS
  In bolus tracking MRI, deconvolution of the concentration-time course can in theory provide accurate quantification. However, there are several important assumptions in the tracer kinetic model used, some of which may be invalid in cerebral ischemia. These can introduce significant errors in perfusion quantification.
  
  
  CONCLUSIONS
  Although we believe that bolus tracking MRI is a powerful technique for the evaluation of perfusion in cerebral ischemia, interpretation of perfusion maps requires caution; this is particularly true when absolute quantification is attempted. Work is currently under way in a number of centers to address these problems, and with appropriate modeling they may be overcome in the future. In the interim, we believe that it is necessary for users of bolus tracking perfusion data to be aware of the current technical limitations if they are to avoid misinterpretation or overinterpretation of their findings.
authors.affiliation: Radiology and Physics Unit, Institute of Child Health, University College London, and Great Ormond Street Hospital for Children National Health Service Trust, London, UK. cfernan@ich.ucl.ac.uk
authors.forename: F
authors.initials: F
authors.lastname: Calamante
authors.forename: D G
authors.initials: DG
authors.lastname: Gadian
authors.forename: A
authors.initials: A
authors.lastname: Connelly
mesh_terms: D002560:Cerebrovascular Circulation; D003287:Contrast Media; D006801:Humans; D008279:Magnetic Resonance Imaging; D008955:Models, Cardiovascular; D011237:Predictive Value of Tests; D020521:Stroke / Q000175:diagnosis*
chemical_list: D003287:Contrast Media