Highly efficient respiratory gating in whole heart MR employing non-rigid retrospective motion correction

Introduction: Three-dimensional whole heart imaging becomes the method of choice in various cardiac applications [1] as it avoids extensive planning of imaging slices and allows reconstructing arbitrary slice orientations. The drawback of the method is a relatively long scan time (on the order of several minutes) which requires motion compensation to suppress motion artifacts. A typical approach to respiratory motion correction uses prospective navigator based gating or triggering including slice tracking. The technique has proven relatively robust; however a lot of data are rejected and only 30-60% of the overall scan time contributes to the reconstructed images. Recently, retrospective approaches have successfully been implemented by extending the image encoding matrix with motion operators and solving the system iteratively [2-4]. This allows for increased gating window widths or even continuous scanning during the entire breathing cycle but necessitates detailed information of the underlying motion vector field during each acquisition. In this work, a template-based approach for non-rigid retrospective motion correction is proposed to correct for respiratory motion artifacts in free-breathing coronary MR scans with gating windows as large as 20mm. The volunteer-specific motion model is computed from a low-resolution multi-slice scan acquired in an interleaved manner simultaneously with the 3D acquisition.