Recovery kinetics of creatine in mild plantar flexion exercise using 3D creatine CEST imaging at 7 Tesla

Purpose Two‐dimensional creatine CEST (2D‐CrCEST), with a slice thickness of 10‐20 mm and temporal resolution (τ Res ) of about 30 seconds, has previously been shown to capture the creatine‐recovery kinetics in healthy controls and in patients with abnormal creatine‐kinase kinetics following the mild plantar flexion exercise. Since the distribution of disease burden may vary across the muscle length for many musculoskeletal disorders, there is a need to increase coverage in the slice‐encoding direction. Here, we demonstrate the feasibility of 3D‐CrCEST with τ Res of about 30 seconds, and propose an improved voxel‐wise ‐calibration approach for CrCEST. Methods The current 7T study with enrollment of 5 volunteers involved collecting the baseline CrCEST imaging for the first 2 minutes, followed by 2 minutes of plantar flexion exercise and then 8 minutes of postexercise CrCEST imaging, to detect the temporal evolution of creatine concentration following exercise. Results Very good repeatability of 3D‐CrCEST findings for activated muscle groups on an intraday and interday basis was established, with coefficient of variance of creatine recovery constants (τ Cr ) being 7%‐15.7%, 7.5%, and 5.8% for lateral gastrocnemius, medial gastrocnemius, and peroneus longus, respectively. We also established a good intraday and interday scan repeatability for 3D‐CrCEST and also showed good correspondence between τ Cr measurements using 2D‐CrCEST and 3D‐CrCEST acquisitions. Conclusion In this study, we demonstrated for the first time the feasibility and the repeatability of the 3D‐CrCEST method in calf muscle with improved correction to measure creatine‐recovery kinetics within a large 3D volume of calf muscle.