title: Flow measurement by cardiovascular magnetic resonance: a multi-centre multi-vendor study of background phase offset errors that can compromise the accuracy of derived regurgitant or shunt flow measurements.
abstract: OBJECTIVE
  Cardiovascular magnetic resonance (CMR) allows non-invasive phase contrast measurements of flow through planes transecting large vessels. However, some clinically valuable applications are highly sensitive to errors caused by small offsets of measured velocities if these are not adequately corrected, for example by the use of static tissue or static phantom correction of the offset error. We studied the severity of uncorrected velocity offset errors across sites and CMR systems.
  
  
  RESULTS
  In a multi-centre, multi-vendor study, breath-hold through-plane retrospectively ECG-gated phase contrast acquisitions, as are used clinically for aortic and pulmonary flow measurement, were applied to static gelatin phantoms in twelve 1.5 T CMR systems, using a velocity encoding range of 150 cm/s. No post-processing corrections of offsets were implemented. The greatest uncorrected velocity offset, taken as an average over a 'great vessel' region (30 mm diameter) located up to 70 mm in-plane distance from the magnet isocenter, ranged from 0.4 cm/s to 4.9 cm/s. It averaged 2.7 cm/s over all the planes and systems. By theoretical calculation, a velocity offset error of 0.6 cm/s (representing just 0.4% of a 150 cm/s velocity encoding range) is barely acceptable, potentially causing about 5% miscalculation of cardiac output and up to 10% error in shunt measurement.
  
  
  CONCLUSIONS
  In the absence of hardware or software upgrades able to reduce phase offset errors, all the systems tested appeared to require post-acquisition correction to achieve consistently reliable breath-hold measurements of flow. The effectiveness of offset correction software will still need testing with respect to clinical flow acquisitions.
authors.affiliation: CMR Unit, Royal Brompton Hospital, London, UK.
authors.forename: Peter D
authors.initials: PD
authors.lastname: Gatehouse
authors.forename: Marijn P
authors.initials: MP
authors.lastname: Rolf
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Graves
authors.forename: Mark Bm
authors.initials: MB
authors.lastname: Hofman
authors.forename: John
authors.initials: J
authors.lastname: Totman
authors.forename: Beat
authors.initials: B
authors.lastname: Werner
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Quest
authors.forename: Yingmin
authors.initials: Y
authors.lastname: Liu
authors.forename: Jochen
authors.initials: J
authors.lastname: von Spiczak
authors.forename: Matthias
authors.initials: M
authors.lastname: Dieringer
authors.forename: David N
authors.initials: DN
authors.lastname: Firmin
authors.forename: Albert
authors.initials: A
authors.lastname: van Rossum
authors.forename: Massimo
authors.initials: M
authors.lastname: Lombardi
authors.forename: Juerg
authors.initials: J
authors.lastname: Schwitter
authors.forename: Jeanette
authors.initials: J
authors.lastname: Schulz-Menger
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Kilner
mesh_terms: D001011:Aorta / Q000503:physiopathology*; D016477:Artifacts; D001783:Blood Flow Velocity; D002302:Cardiac Output; D005780:Gelatin; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D019028:Magnetic Resonance Imaging, Cine / Q000295:instrumentation*; D008422:Materials Testing; D008944:Mitral Valve Insufficiency / Q000175:diagnosis* / Q000503:physiopathology; D019047:Phantoms, Imaging; D011237:Predictive Value of Tests; D011651:Pulmonary Artery / Q000503:physiopathology*; D015203:Reproducibility of Results; D015656:Respiratory Mechanics
chemical_list: D005780:Gelatin