Purpose To test the feasibility of cardiac real‐time MRI in combination with retrospective gating by MR‐compatible spirometry, to improve motion control, and to allow quantification of respiratory‐induced changes during free‐breathing. Methods Cross‐sectional real‐time MRI (1.5T; 30 frames/s) using steady‐state free precession contrast during free‐breathing was combined with MR‐compatible spirometry in healthy adult volunteers (n = 4). Retrospective binning assigned images to classes that were defined by electrocardiogram and spirometry. Left ventricular eccentricity index as an indicator of septal position and ventricular volumes in different respiratory phases were calculated to assess heart–lung interactions. Results Real‐time MRI with MR‐compatible spirometry is feasible and well tolerated. Spirometry‐based binning improved motion control significantly. The end‐diastolic epicardial eccentricity index increased significantly during inspiration (1.04 ± 0.04 to 1.19 ± 0.05; P < .05). During inspiration, right ventricular end‐diastolic volume (79 ± 17 mL/m2 to 98 ± 18 mL/m2), stroke volume (41 ± 8 mL/m2 to 59 ± 11 mL/m2) and ejection fraction (53 ± 3% to 60 ± 1%) increased significantly, whereas the end‐systolic volume remained almost unchanged. Left ventricular end‐diastolic volume, left ventricular stroke volume, and left ventricular ejection fraction decreased during inspiration, whereas the left ventricular end‐systolic volume increased. The relationship between stroke volume and end‐diastolic volume (Frank‐Starling relationship) based on changes induced by respiration allowed for a slope estimate of the Frank‐Starling curve to be 0.9 to 1.1. Conclusion Real‐time MRI during free‐breathing combined with MR‐compatible spirometry and retrospective binning improves image stabilization, allows quantitative image analysis, and importantly, offers unique opportunities to judge heart–lung interactions.

Background Cardiac real-time magnetic resonance imaging (RT-MRI) provides high-quality images even during free-breathing. Difficulties in post-processing impede its use in clinical routine. Objective To demonstrate the feasibility of quantitative analysis of cardiac free-breathing RT-MRI and to compare image quality and volumetry during free-breathing RT-MRI in pediatric patients to standard breath-hold cine MRI. Materials and methods Pediatric patients (n = 22) received cardiac RT-MRI volumetry during free breathing (1.5 T; short axis; 30 frames per s) in addition to standard breath-hold cine imaging in end-expiration. Real-time images were binned retrospectively based on electrocardiography and respiratory bellows. Image quality and volumetry were compared using the European Cardiovascular Magnetic Resonance registry score, structure visibility rating, linear regression and Bland–Altman analyses. Results Additional time for binning of real-time images was 2 min. For both techniques, image quality was rated good to excellent. RT-MRI was significantly more robust against artifacts (P < 0.01). Linear regression revealed good correlations for the ventricular volumes. Bland–Altman plots showed a good limit of agreement (LoA) for end-diastolic volume (left ventricle [LV]: LoA -0.1 ± 2.7 ml/m2, right ventricle [RV]: LoA -1.9 ± 3.4 ml/m2), end-systolic volume (LV: LoA 0.4 ± 1.9 ml/m2, RV: LoA 0.6 ± 2.0 ml/m2), stroke volume (LV: LoA -0.5 ± 2.3 ml/m2, RV: LoA -2.6 ± 3.3 ml/m2) and ejection fraction (LV: LoA -0.5 ± 1.6%, RV: LoA -2.1 ± 2.8%). Conclusion Compared to standard cine MRI with breath hold, RT-MRI during free breathing with retrospective respiratory binning offers good image quality, reduced image artifacts enabling fast quantitative evaluations of ventricular volumes in clinical practice under physiological conditions.

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