- Technologist presentation
- Open Access
Background offset error in pulmonary and aortic phase contrast flow imaging of 94 patients
© Dahl et al; licensee BioMed Central Ltd. 2010
Published: 21 January 2010
Velocity-encoding generates small eddy currents causing background offset errors (recognised as velocity of stationary tissue). Chernobelsky et al. (2007) assessed background offset correction on 10 volunteers, demonstrating that offset errors ≈1% of VENC can cause up to 25% errors during measurements. No larger studies have yet measured this error.
Patients were scanned at 1.5T (Siemens Avanto VB15, 12-channel phased-array coil) with a retrospectively ECG-gated, breath-hold flow sequence (turbo-factor 6, TR10/TE2.3ms, 698Hz/pixel, flip angle 25°, FOV 320-360mm, 1.3x2.5mm at 320mmFOV, 10mm SLT, Maxwell-correction, no other background-correction, VENC 80-420 (avg.175)cm/s). Oblique aortic and/or pulmonary flow studies in 94 patients were reproduced using a stationary jelly-phantom, with the exact imaging parameters used in-vivo including individual ECG simulations. Through-plane flow was calculated (CMRtools, CVIS) by outlining the cross-sectioned vessel and adding volume flow over the cardiac cycle. The region of interest was copied onto the phantom image to find the background offset in ml/beat. During each scan the couch moved automatically to zero the head-foot (z-) location; this should always have placed the vessel of interest at z=0 but residual head-foot vessel locations were recorded. Correlations between the background offset and relevant study parameters were tested.
Results and discussion
In this protocol, uncorrected background offset error would have caused 10% or greater error in approximately 10% of the studies, degrading the reliability of large vessel flow, requiring careful consideration of correction methods.
This article is published under license to BioMed Central Ltd.