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 FDA-approved Drug Library clinical trial 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 Cyclic nucleotide phosphodiesterase used to bolster signal to noise ratio (SNR) in the images and to move any characteristic spiral artifacts selleck compound 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.