Spirometry‐based reconstruction of real‐time cardiac MRI: Motion control and quantification of heart–lung interactions

Abstract

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.

Comparison of cardiac volumetry using real-time MRI during free-breathing with standard cine MRI during breath-hold in children

“…Previous RT-MRI studies during free-breathing demonstrated that even with calm breathing, respiration influences cardiac function [ 9 , 10 , 30 ]. The RV was especially affected significantly [ 9 , 10 ].…”

“…Thus, the heart position varied in images with equal respiratory bellows values resulting in greater movement from image to image in RT-MRI. MR-compatible spirometry could provide quantitative information on respiratory flow in future studies [ 9 ].…”

“…L.M.R. performed manual corrections based on a standardized approach at the Children’s University Hospital, University Hospital Duesseldorf, Germany [ 9 ] that was established considering current recommendations on cardiac image analysis [ 16 – 19 ]. To test intra- and inter-rater reliability for the LV and RV volume evaluation, L.M.R.…”

“…Since cardiac RT-MRI allows for data acquisition during free breathing, it greatly enhances the convenience of cardiac MRI for all patients and simplifies the investigation of young pediatric patients. Furthermore, the examination takes place under physiological conditions, which improves the informative value of cardiac function regarding heart–lung interactions [ 9 , 10 ].…”

Chest examinations in children with real-time magnetic resonance imaging: first clinical experience

“…The recent introduction of a specific real-time MRI technique, fast low-angle shot technique 2.0 (FLASH 2.0), in two pediatric radiology departments in Germany has enabled such a high frame rate for daily routine evaluation [9] of moving organs such as the heart and joints, as well as for visualizing speech [10]. Of high clinical impact, this novel technique has recently been adopted to avoid motion artifacts in cranial MR examinations of non-sedated moving infants and young children [11].…”