9 ms and TR=23 ms) preceded by a 15° FE pulse, resulting in a 135-ms low-resolution acquisition window. The resolution was 4.8×4.8×3 mm at 261×261×24 mm field of view, reconstructed to 0.5×0.5×1.5 mm. Each high-resolution segment consisted of two interleaves of a 75-interleave 3D center-out spiral acquisition with eight through-plane phase encode steps. The first interleaf of each segment was acquired with a 45° WE pulse and the second with a 90° WE pulse. Each interleave consisted of 4096 points acquired over 10 ms (TE=3.4 ms and TR=1 RR interval). A spatial saturation pulse was applied to the chest wall immediately prior to the high-resolution imaging segment in order to minimize artifacts from structures not moving

with the coronary artery. The high-resolution data were temporally located in the subject-specific right coronary rest period. Where possible, the low-resolution GW572016 data were also acquired during this period of minimal motion, but the timing of the high-resolution data was prioritized. As the low-resolution data are acquired in a reverse-centric kz phase order, the effect of any motion during the low-resolution acquisition is expected to be minimal. The total acquisition duration was 300 cardiac cycles (assuming 100% respiratory efficiency) or 5 min (with a heart rate of 60 beats/min). The acquired resolution was 0.7×0.7×3 mm over a 570×570×24

mm field of view which was reconstructed to a 0.7×0.7×1.5 mm pixel size. The high field of view was Hydroxychloroquine mw used to bolster signal to noise ratio (SNR) in the images and to move any characteristic spiral artifacts PLX-4720 cost away from the anatomy of interest. The high-resolution acquisition window was 35 ms. All images were reconstructed and processed offline using in-house software written in MATLAB 2009a (The Mathworks, Natick, MA). Beat-to-beat 3D respiratory displacement of the right coronary artery was determined using a 3D local normalized subpixel cross-correlation of the low-resolution volumes acquired in each cardiac cycle. An end

expiratory volume was chosen as a reference using the diaphragmatic navigator information. A cuboid-shaped reference region around the coronary origin was defined on the reference volume, aided by a colored overlay of the fat image on the uncorrected high-resolution water image, as seen in Fig. 3. A search region was also defined on this volume and copied to the other low-resolution volumes for the subsequent beat-to-beat cross-correlation. In order to determine the appropriate dimensions for the search region, the cross-correlation was initially performed on a subset of 20 of the low-resolution volumes before performing the full procedure. The two high-resolution spiral interleaves acquired in each cardiac cycle were corrected [2] for respiratory motion using the 3D beat-to-beat translations obtained, and high-resolution images were reconstructed using a standard gridding [27] and fast Fourier transform technique.