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.
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.
Gatehouse
Peter D
PD
CMR Unit, Royal Brompton Hospital, London, UK.
Rolf
Marijn P
MP
Graves
Martin J
MJ
Hofman
Mark Bm
MB
Totman
John
J
Werner
Beat
B
Quest
Rebecca A
RA
Liu
Yingmin
Y
von Spiczak
Jochen
J
Dieringer
Matthias
M
Firmin
David N
DN
van Rossum
Albert
A
Lombardi
Massimo
M
Schwitter
Juerg
J
Schulz-Menger
Jeanette
J
Kilner
Philip J
PJ
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
D005780:Gelatin