MR ‐based in vivo follow‐up study of A chilles tendon volume and hydration state after ankle‐loading activity

The purpose of this study was to evaluate temporal alterations of the A chilles tendon volume and hydration state after cross‐country‐running. A chilles tendons of six untrained participants were examined on a 3 T MR ‐scanner before running, immediately afterwards, and in the following 24, 48, and 72 h. Using a 3 D ‐ UTE sequence, caudal ( CA ) and cranial ( CR ) mid‐portion tendon areas were examined with off‐resonance saturation ratios ( OSR ) and T 2* relaxation times. Tendon volume was measured with a self‐written M atlab‐based automated contour detection algorithm ( AVAT ) in submillimeter T 2‐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 T 2* measurements ( P  = 0.046), but not in caudal T 2* 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 A chilles tendon, an increase with a maximum free water content 48 h after ankle loading and a tendency toward normalization after 72 h was found.