Abstract 10901: 4D Flow versus 2D Cardiac MRI for the Evaluation of Pulmonary Regurgitation and Ventricular Volume in Repaired Tetralogy of Fallot.

Background: Limitations of traditional 2D cardiac MRI (2D CMR) are breath holding and long exam times. 3D time-resolved flow (4DF) MRI is a 5-10 minute, free-breathing, single-sequence exam that simultaneously collects magnitude and phase contrast data. Our primary objective is to compare the precision of gadobenate dimeglumine enhanced 4DF CMR obtained on a 1.5-T MRI with 2D CMR in patients with repaired tetralogy of Fallot (rTOF) to measure pulmonary net flow (PNF), sum of forward flow (FF) and regurgitant flow. Secondary objectives were to compare agreements for ventricular size and function. Methods: Via a retrospective case control study design, a blinded observer segmented 2D and 4DF images from rTOF patients (n=34). For 2D CMR, ventricular volume and function were measured on short-axis SSFP images and flow on phase contrast images at the aortic (AoV) and pulmonary valve (PV). For 4D CMR, ventricular volume and function were measured on simulated short axis acquisitions. Flow measurements were made at the AoV, PV, main pulmonary artery (MPA), and branch pulmonary arteries (BPA). Results: Assessment of PNF using 4DF at the PV demonstrated the strongest correlation (r=0.87) and lowest mean difference (3.5 ± 9.4 ml/beat) to aortic net flow. FF and stroke volume correlated moderately-strongly with 4DF (r=0.68-0.80, p<0.001) and 2D acquisitions (r=0.79-0.81, p<0.001) with no significant difference in correlation coefficients (Fisher's transformation, p>0.12) or mean differences (p>0.24) between techniques. Comparison of 2DF and 4DF ventricular volume measurements demonstrated strong correlations (r=0.75-0.96) and ejection fraction demonstrated moderate correlation (r=0.60-0.75). Right ventricular (RV) volumetry by 4DF demonstrated strong correlation (r=0.95-0.96) with 2D SSFP, but overestimated values (11.8-19.2 mL/beat). Average time to complete 2D CMR was 71.2 ± 18.8 minutes vs. 9.2 ± 1.3 for 4DF acquisitions (p<0.001). Conclusions: In patients with rTOF, 4DF CMR obtained using commonly available techniques is comparably precise to 2D CMR for evaluation of PNF and ventricular volumes with slight overestimation of RV volumes. When RV systolic function is normal on echo, 4DF may be considered as a stand-alone sequence for interval assessments. [ABSTRACT FROM AUTHOR]