Short-term exercise-induced changes in hydration state of healthy Achilles tendons can be visualized by effects of off-resonant radiofrequency saturation in a three-dimensional ultrashort echo time MRI sequence applied at 3 Tesla.
OBJECTIVE
Off-resonant RF saturation influences signal intensity dependent on free and bound water fractions as well as the macromolecular content. The extent of interaction between these compartments can be evaluated by using the off-resonance saturation ratio (OSR). Combined with UTE sequences quantification of OSR even in tendinous tissues with extremely fast signal decay is possible. The aim of this prospective study was to investigate short-term exercise-induced effects of hydration state of the Achilles tendon by means of OSR and tendon volume.


METHODS
Measurements of OSR and tendon volume before and after ankle-straining activity were performed in seven healthy male volunteers (median age 29 years) using a 3D UTE sequence with implemented off-resonance saturation pulse at 3T (off-resonance frequency 2/3 kHz) and by an automated contour detection in isotropic T2-weighted MR images with sub-millimeter resolution, respectively. Different tendon regions were evaluated. Reproducibility of OSR was measured in subsequent imaging sets. Root-mean-square-deviation (RMSD) and coefficient of variations (CV) were determined.


RESULTS
RMSD of OSR in resting position were between 0.006 and 0.01 for different tendon regions and off-resonance frequencies (CV 2 to 3%). A significant increase (P < 0.05) of OSR after exercise was seen in all tendon regions except at the insertion (off-resonance frequency 3 kHz). Tendon volume was decreased significantly after ankle-straining activity (P = 0.003).


CONCLUSIONS
The observed decreased tendon volume and increased OSR directly after exercise indicates a short-term change in tendinous proton compartments, most likely a loss of free water molecules within the tendon.
Diagnostic and Interventional Radiology, Eberhard-Karls-University, Tübingen, Germany; Section on Experimental Radiology, Eberhard-Karls-University, Tübingen, Germany.
Roland
R
Syha
Fabian
F
Springer
Gerd
G
Grözinger
Christian
C
Würslin
Ingmar
I
Ipach
Dominik
D
Ketelsen
Christoph
C
Schabel
Harry
H
Gebhard
Tobias
T
Hein
Petros
P
Martirosian
Fritz
F
Schick
Claus D
CD
Claussen
Ulrich
U
Grosse
D000125:Achilles Tendon / Q000033:anatomy & histology* / Q000502:physiology*; D000328:Adult; D000465:Algorithms; D001834:Body Water / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009929:Organ Size; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult
Achilles tendon; MRI; UTE imaging; exercise; magnetization transfer; running; tendons