Introduction Accuracy of through plane phase-contrast flow mapping (PCFM) is vital for assessment of cardiac output and valve regurgitation. Standardised SCMR protocols specify only that PCFM should be centred in the vessel, aligned orthogonally to flow but do not specify location relative to the aortic valve (AV). A previous study suggested variation in stroke volume (SV) based on distance from the AV but included only patients with valve disease. The aim of this study was to determine the location of PCFM which best corresponds to LV SV.
Methods Through-plane breath-hold PCFM was performed (1.5 T Siemens, Avanto) in 10 healthy volunteers (7 female; mean age 33±9 years): 6 mm sub-AV; at AV tips, 6 mm, 12 mm and 18 mm distally. Images were independently analysed (Circle CVi42, Canada) by 2 experienced observers. SV was compared with the LV SV as a gold standard.
Results SV at the AV tips showed the highest correlation with LV SV (ICC=0.964), and 18 mm above AV the lowest correlation (ICC=0.896). SVol progressively fell distally: 7.2 ml (8%) at 12 mm; 10.8 ml (11%) at 18 mm. PCFM taken 6 mm below the AV underestimates SV by 6.2 ml (6%). The ICC for all aortic flow map stroke volumes between both analysers was 0.975.
Conclusion Measurement of SV by through-plane PCFM is dependent on position, with progressive fall as distance increases from the AV. Measurement at the leaflet tips of the AV corresponds closest to the LV SV.
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