title: Magnetic resonance measurement of blood and CSF flow rates with phase contrast--normal values, repeatability and CO2 reactivity.
abstract: BACKGROUND
  Similarity in flow pulsatility has been proposed as a basis for semi-automated segmentation of vessel lumens for MR-based flow measurement, but re-examinations of salient aspects of the methodology have not been widely reported.
  
  
  METHODS
  12 normal control subjects underwent repeated (3*Baseline+1*5%CO2) phase contrast measurements of CSF flow through the cerebral aqueduct and foramen magnum, and CBF through the 6 large cranial vessels at the level of the 1st vertebra. Average flows were calculated for regions temporally correlated (0.3 < or = Rthreshold < or = 0.95) to user defined seed points and their 3 x 3 neighbours.
  
  
  RESULTS
  Arterial CBF averaged 710ml/min, with low variability (+/- 4%/17%, intra-individual/group CV respectively) and was the only flow to respond significantly to 5%/mmHg CO2. Venous outflow was much smaller (298ml/min +/- 10%/ 72%), possibly due to the weak venous pulse and variable venous anatomy. Average CSF flows exceeded the classical 0.4ml/min CSF production rate and were highly variable--aqueduct: 0.6ml/min (+/- 50%/93%), foramen magnum: -2.7ml/min (+/- 158%/226%).
  
  
  CONCLUSIONS
  This preliminary analysis identified procedural steps that can improve the accuracy and repeatability of MR flow measurements, but the process remains user-dependent for the weakly pulsatile foramen magnum CSF and venous flows where variability remains a significant confound even to relatively large perturbations such as CO2 administration.
authors.affiliation: Department of Clinical Neurology, Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB), University of Oxford, John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK. stefanp@fmrib.ox.ac.uk
authors.forename: Stefan K
authors.initials: SK
authors.lastname: Piechnik
authors.forename: Paul E
authors.initials: PE
authors.lastname: Summers
authors.forename: Peter
authors.initials: P
authors.lastname: Jezzard
authors.forename: James V
authors.initials: JV
authors.lastname: Byrne
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology*; D001808:Blood Vessels / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism*; D002535:Cerebral Aqueduct / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D005539:Foramen Magnum / Q000502:physiology; D006801:Humans; D007089:Image Enhancement; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D012016:Reference Values; D015203:Reproducibility of Results
chemical_list: D002245:Carbon Dioxide