MR-based in vivo follow-up study of Achilles tendon volume and hydration state after ankle-loading activity

The purpose of this study was to evaluate temporal alterations of the Achilles tendon volume and hydration state after cross-country-running. Achilles tendons of six untrained participants were examined on a 3T MR-scanner before running, immediately afterwards, and in the following 24, 48, and 72 h. Using a 3D-UTE sequence, caudal (CA) and cranial (CR) mid-portion tendon areas were examined with off-resonance saturation ratios (OSR) and T2* relaxation times. Tendon volume was measured with a self-written Matlab-based automated contour detection algorithm (AVAT) in submillimeter T2-weighted MR images. A significant influence of running in caudal (P = 0.017) and cranial OSR values (P = 0.001), tendon volume (P = 0.024), and cranial T2* measurements (P = 0.046), but not in caudal T2* values (P = 0.298) were found. In detail, mean individual OSR and tendon volume measurements demonstrated a similar but inverted course in their values after exercise: initially, OSR values increased after running (and tendon volume decreased), while subsequently a decrease of OSR values (with an increase of tendon volume) could be observed. OSR and tendon volume measurements are able to detect a physiological response of tendons to a mechanical stimulus. After a transient decrease of free water in the Achilles tendon, an increase with a maximum free water content 48 h after ankle loading and a tendency toward normalization after 72 h was found.