title: Quantitative perfusion measurements using pulsed arterial spin labeling: effects of large region-of-interest analysis.
abstract: OBJECTIVE
  To study arterial spin labeling (ASL) MRI techniques and to investigate various problematic issues that still hinder the accurate and robust quantitative analysis of ASL data.
  
  
  METHODS
  A pulsed-ASL (PASL) sequence was implemented on a 3-T imaging system and a protocol was developed for the measurement of perfusion based on fitting to a standard kinetic model. Both numerical simulations and multi-inversion time MRI data were analyzed. The effect of fitting a kinetic curve to a large region of interest (ROI) with a distribution of arterial transit times was compared to a pixel-by-pixel (PBP) method.
  
  
  RESULTS
  It was found that a significant underestimation of perfusion of approximately 17+/-6% (P<0.001) occurs in gray matter, when comparing an ROI with a PBP analysis over a group of 12 healthy subjects.
  
  
  CONCLUSIONS
  Analysis of ASL data based on a large ROI may suffer from inaccuracies arising from a distribution of transit times, implying that averaging of ASL kinetic data over such regions should therefore be avoided. When possible, a PBP fit should be performed.
authors.affiliation: Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB), Department of Clinical Neurology, University of Oxford, John Radcliffe Hospital, Oxford, UK.
authors.forename: Patrícia M
authors.initials: PM
authors.lastname: Figueiredo
authors.forename: Stuart
authors.initials: S
authors.lastname: Clare
authors.forename: Peter
authors.initials: P
authors.lastname: Jezzard
mesh_terms: D000328:Adult; D002560:Cerebrovascular Circulation; D003198:Computer Simulation; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008962:Models, Theoretical; D013113:Spin Labels
chemical_list: D013113:Spin Labels