Pseudo-projection–driven, self-gated cardiac cine imaging using cartesian golden step phase encoding

Purpose: To develop and evaluate a novel two-dimensional self-gated imaging technique for free-breathing cardiac cine MRI that is free of motion-detection overhead and requires minimal planning for motion tracking. Methods: Motion along the readout direction was extracted solely from normal Cartesian imaging readouts near k_y = 0. During imaging, the readouts below a certain |k_y| threshold were scaled in magnitude and filtered in time to form “pseudo-projections,” enabling projection-based motion tracking along readout without frequently acquiring the central phase encode. A discrete golden step phase encode scheme allowed the |k_y| threshold to be freely set after the scan while maintaining uniform motion sampling. Results: The pseudo-projections stream displayed sufficient spatiotemporal resolution for both cardiac and respiratory tracking, allowing retrospective reconstruction of free-breathing non-electrocardiogram (ECG) cines. The technique was tested on healthy subjects, and the resultant image quality, measured by blood-myocardium boundary sharpness, myocardial mass, and single-slice ejection fraction was found to be comparable to standard breath-hold ECG-gated cines. Conclusion: The use of pseudo-projections for motion tracking was found feasible for cardiorespiratory self-gated imaging. Despite some sensitivity to flow and eddy currents, the simplicity of acquisition makes the proposed technique a valuable tool for self-gated cardiac imaging. Magn Reson Med 76:417–429, 2016.