Continuous Ventricular Volumetric Quantification in Patients with Arrhythmias using Real-Time 3D CMR-MOTUS

Conventional cardiovascular magnetic resonance (CMR) cine sequences rely on binning reconstructions that average multiple heartbeats, an assumption that breaks down in arrhythmic patients where beat-to-beat variations lead to motion artifacts and loss of clinically relevant functional information. While 2D real-time imaging can capture individual heartbeats, a stack of 2D slices is sub-optimal to map the full complexity of incoherent cardiac dynamics during arrhythmia. We demonstrate the feasibility of 3D real-time motion field reconstruction for continuous beat-to-beat volumetric quantification in patients with premature ventricular contractions (PVC) using a free-running CMR protocol.

We extended CMR-MOTUS to jointly reconstruct real-time 3D motion fields and a motion-corrected reference image from continuously acquired data without breath-holds or ECG gating. A variable-density Cartesian sampling trajectory (OPRA) was used with a 3D spoiled gradient echo or balanced steady-state free precession sequence. The real-time volumetric beat-to-beat changes were quantified by propagating a single manual segmentation on the reference image, through all time frames using the reconstructed motion fields. The method was validated on a cardiac motion phantom with ground-truth static acquisitions and tested in 4 healthy volunteers and 4 patients with PVC. The ejection fraction (EF) was compared to ground-truth values for the phantom and to standard 2D real-time cine EF measurement techniques for in-vivo subjects.

Reconstructed EF values of the phantom experiment showed good agreement with the ground-truth(EF = 22.1 ± 0.6% versus 21.9%). In healthy volunteers, the mean EF values were close to 2D reference measurements and narrow beat-to-beat EF distributions reflected normal physiological consistency. In PVC patients, the method revealed bimodal EF distributions, with the lower mode corresponding to PVC episodes where individual beats had substantially reduced ejection fractions. Simultaneously acquired ECG signals confirmed the temporal correspondence between volume irregularities and PVC episodes.

3D real-time joint motion field and image reconstruction from a free-running CMR protocol enables continuous beat-to-beat volumetric quantification in arrhythmic patients, revealing functional heterogeneity that conventional single-beat and averaging measurements (binning and gating) obscure. The bimodal EF distributions observed in PVC patients quantify the true hemodynamic impact of arrhythmic episodes and may provide clinically relevant metrics for treatment monitoring and outcome prediction.