In Vivo Study

For in vivo experiments, the RCA was imaged in 10 healthy adult subjects (ages 19–32, 6 female). Permission from the Institutional Review Board was obtained for all in vivo scans, and written informed consent was obtained from all volunteers prior to the procedure. Imaging parameters were as in the phantom vessel sharpness experiments, though only acceleration factors of R = 1,3, and 6 were compared due to time constraints. Additionally, the experiments were both respiratory- and ECG-gated, with an end-expiratory navigator gating acceptance window of ±2 mm selected to minimize respiratory motion artefacts, using a slice tracking factor of 0.60 [46]. The scan times varied for each volunteer, depending on heart rate and respiratory pattern (i.e. end-expiratory percentage), with each acquisition taking 384 heartbeats to acquire for an R = 1 [(8 segments/heartbeat)^-1 * 384 segments/z-partition * 8 z-partitions/acquisition]. Thus, for a heart rate of 72 BPM and a respiratory acceptance of 40%, one can calculate the base scan duration to be 13min20s [384 heartbeats * (72 heartbeats/min)^-1 * (0.4)^-1], 4min27s for R = 3, and 2min13s for R = 6. Similar to the phantom vessel sharpness experiments, all images were reformatted and analyzed using the Soap-Bubble quantitative software tool [45]. For each volunteer, a continuous section of the coronary was identified, both visually and with Sopabubble, where VS could be evaluated across that section using either T₂-Prep technique, and the % differences in VS was calculated for each acceleration factor. A paired 2-tailed Student’s t-test was used to compare these VS differences, with a P < 0.05 considered statistically significant.