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Abstract
BackgroundFlow mapping by cardiovascular magnetic resonance has become the gold standard for non-invasively defining cardiac output (CO), shunt flow and regurgitation. Previous reports have highlighted the presence of inherent errors in flow mapping that are improved with the use of a stationary phantom control. To our knowledge, these studies have only been performed in healthy volunteers.ResultsWe analyzed the variation in flow measurements made with and without stationary phantom correction in 31 patients with congenital heart disease. Variation in stroke volume (SV) measurements was seen in all vessels across all patient groups. The variation was largest when analyzing the right ventricular outflow tract (RVOT), with a range of absolute differences in SV from 0.2 to 70 ml and in CO from 0.02 to 4.8 L/min. In patients with repaired Tetrology of Fallot (ToF), the average ratio of pulmonary to systemic blood flow (Qp:Qs) was 1.18 without and 1.02 with phantom correction. Without performing phantom correction, 23% of the repaired ToF patients were classified as having a residual shunt as compared to 0% when flow mapping was performed with phantom correction. Similarly, in patients with known atrial level shunting (ASD/PAPVR) 20% of patients had no shunt when flow mapping was performed without phantom correction as compared to 0% with phantom correction. In patients with bicuspid aortic valves (BAV), the differences in the regurgitant fraction between measuring flow with and without phantom correction ranged from 0 to 30%, while the regurgitant fraction in the RVOT of ToF patients varied by as much as 31%.ConclusionThe impact of inherent errors in CMR flow mapping should not be underestimated. While the variation across a population may not display a significant trend, for any individual patient it can be quite large. Failure to correct for such variation can lead to clinically significant misinterpretation of flow data. The use of the stationary phantom correction technique appears to improve accuracy both in normal patients as well as those with congenital heart disease.
Highlights
Flow mapping by cardiovascular magnetic resonance has become the gold standard for non-invasively defining cardiac output (CO), shunt flow and regurgitation
Patient Selection and Internal Control During the time of our study there were 20, 11 and 10 patients evaluated by cardiovascular magnetic resonance (CMR) for Tetrology of Fallot (ToF), bicuspid aortic valves (BAV) and atrial level shunting, respectively
In the ToF group, 4 patients were excluded from all analysis due to arrhythmias making gating inaccurate, 2 patients were excluded from analysis involving the branch pulmonary arteries (BPAs) secondary to heart rate variability and BPAs moving in and out of plane, 1 patient was excluded from analysis involving aortic flow secondary to artifact from sternal wires
Summary
Flow mapping by cardiovascular magnetic resonance has become the gold standard for non-invasively defining cardiac output (CO), shunt flow and regurgitation. Previous reports have highlighted the presence of inherent errors in flow mapping that are improved with the use of a stationary phantom control To our knowledge, these studies have only been performed in healthy volunteers. Flow mapping by CMR has both technical and clinical sources of error including sampling rate, partial volume averaging, sub-optimal velocity encoding selection, flow-turbulence, aliasing and intra-study heart rate changes [5]. These errors are well recognized and attempts are made to minimize their impact during data acquisition and post-processing analysis. When these sources of error are unable to be controlled, comments are made in final reports regarding their effects on study interpretation
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