Motion artifact reduction and vessel enhancement for free‐breathing navigator‐gated coronary MRA using 3D k‐space reordering

Abstract

Breathing-induced bulk motion of the myocardium during data acquisition may cause severe image artifacts in coronary magnetic resonance angiography (MRA). Current motion compensation strategies include breath-holding or free-breathing MR navigator gating and tracking techniques. Navigator-based techniques have been further refined by the applications of sophisticated 2D k-space reordering techniques. A further improvement in image quality and a reduction of relative scanning duration may be expected from a 3D k-space reordering scheme. Therefore, a 3D k-space reordered acquisition scheme including a 3D navigator gated and corrected segmented kspace gradient echo imaging sequence for coronary MRA was implemented. This new zonal motion-adapted acquisition and reordering technique ( Coronary MR angiography (MRA) image quality is heavily dependent on the suppression of breathing-related motion artifacts. The adverse impact of breathing-induced myocardial bulk motion can be minimized by the use of breathholding (1-5) or by the application of respiratory gating with MR navigators (6 -12). Further refinements in navigator technology have included prospective adaptive motion correction (9,10) in conjunction with navigator displacement-dependent 2D reordering of the acquired k yprofiles in k-space (13,14).k-Space reordering techniques take advantage of the inhomogeneous signal distribution in k-space, with highest signal amplitudes in the origin of k-space and gradually decreasing information content in the periphery of k-space (15). However, high-frequency portions of k-space may still contain information relevant to small-diameter structures, such as the coronary arteries. Based on this a priori knowledge, the priority of lines in k-space can be defined by a problem-specific priority function. One such application, among other techniques (6,13,14,16), is motionadapted gating (MAG) for navigator displacement-dependent reordering of k y -profiles in k-space (13). With MAG, "important" profiles are acquired during a small diaphragmatic displacement while profiles of "lesser importance" are subject to broader or larger displacement conditions. Planar 2D phase-reordering methods in 3D coronary MRA minimize respiratory motion artifacts and increase scan efficiency (14). However, these 3D acquisition techniques solely include reordering of the k-space in two dimensions (k x and k y ). We hypothesized that a "true" 3D k-space reordering in conjunction with a 3D imaging approach would lead to further improvements in respiratory motion suppression and a reduction in the relative scanning time.The present study describes a prospective navigatorbased 3D k-space reordering technique. This zonal motionadapted acquisition and reordering technique (ZMART) was developed using simulations of the Bloch equations, and has been validated in phantom and in vivo experiments. Image data were objectively and quantitatively compared, and the preliminary in vivo results are presented. METHODS k-Space ReorderingA prospective adaptive reordering o...

Artifacts in body MR imaging: their appearance and how to eliminate them

“…This is called chemical shift artifact of the first kind (Figs. 18,19). The actual spatial difference is further defined by the bandwidth and the matrix.…”

“…If the movement is sufficiently periodic it is possible to gate the sequence to the movement, for example the respiratory or cardiac cycle [18][19][20]. For imaging of the heart or the great vessels, this can be done by triggering the acquisition of phase encoding steps at a fixed time in the cardiac cycle, which means that in every phase encoding step the structure is in the same position.…”

Current Status of 3-T Cardiovascular Magnetic Resonance Imaging

“…55 Irrespective of the method used, the requirement for high-spatial resolution imaging, combined with the narrow acceptance windows imposed by electrocardiogram gating (targeted to the 80-to 100-millisecond window of relative cardiac rest during mid-diastole), make reliable coronary imaging a challenge. In an attempt to expedite data acquisition, investigators have implemented k-space reordering, 56 3-dimensional (3D) motion-adapted gating, 57 and parallel imaging techniques, such as SENSE. 58 Each of these approaches has shown incremental reduction in overall imaging time, which, however, is still measured in minutes rather than the more desirable situation of requiring seconds for acquisition.…”

Supine breast MRI

“…The breast images were acquired with a fast 3D gradient echo sequence (SPGR), which is frequently used for DCE breast MRI (16). To compensate for the respiratory motion of the breast in the supine position, the fast 3D SPGR sequence was modified in accordance with ZMART (15), which is a combination of phase-encode reordering and gating.…”