Pixel-wise derivation of pulmonary regurgitation index could influence clinical decision: A phase-contrast MR imaging study on patients with repaired tetralogy of Fallot

Purpose Regurgitant fraction (RF) measured from 2D phase-contrast MRI has been used as a standard to quantitate the degree of pulmonary regurgitation and serves as a determinant indicator of prognosis for tetralogy of Fallot after surgical repair. This study demonstrated the potential underestimate of RF using the conventional definition and its impact on clinical decision when backward flow occurred during systolic periods. Methods Quantitative flow parameters, including forward flow volume (FFV), backward flow volume (BFV), and RF were estimated by two approaches: One derived from conventional ROI-averaged curve (bulk quantity) and the other in a pixel-wise manner to spatially reflect inhomogeneous flow profile (pixel-wise quantity). Eccentricity at systolic peak (Ecc_sys) was adopted as an index reflecting spatial flow inhomogeneity. Results Flow parameters derived from ROI-averaged curves on main pulmonary artery were significantly smaller than that of pixel-wise measurement (P<0.001). Difference between RF_bulk and RF_px for the group of Ecc_sys > 0.3 appears greater compared to the group with Ecc_sys < 0.3. Thirteen out of 68 RF values (19%) were underrated while using bulk analysis. Conclusions The spatial-related flow parameters showed more consistency with the qualitative flow profile pattern for pulmonary arteries, and could be a decisive complement for diagnostic classification.