title: Influence of physical activity on T1 and T2* relaxation times of healthy Achilles tendons at 3T.
abstract: OBJECTIVE
  To evaluate longitudinal (T1) and transverse (T2*) relaxation times at different Achilles tendon locations (insertion, mid-portion, and musculotendinous area) in a cohort of subjects with variable tendon straining activity, but without any signs of tendinopathy.
  
  
  METHODS
  T1 and T2* relaxation times of the Achilles tendon were measured using an ultrashort echo time (UTE) imaging sequence with flip angle and echo time variation on a 3T whole-body clinical magnetic resonance (MR) scanner. Twenty-four tendons of 12 healthy volunteers and 18 tendons of nine healthy recreational long-distance runners (average weekly running distance of 47.4 ± 5.3 km) were enrolled.
  
  
  RESULTS
  Mean T1 values of the whole tendon showed no marked group differences, whereas T2* relaxation times of runners were significantly longer (mean percentage increase 15.7 ± 4.9%; P = 0.0181) compared to controls. Regarding group differences for the investigated insertional, mid-portion, and musculotendinous area of the Achilles tendon, only the mid-portion of the Achilles tendon in the running group presented significantly longer T2* values (mean percentage increase 29.1 ± 23.0%; P = 0.0420) in comparison to the control group.
  
  
  CONCLUSIONS
  Prolonged T2* values especially in the mid-portion of the Achilles tendon of runners are likely to reflect an adaptation of the tendon microstructure to repetitive tendon straining activity.
authors.affiliation: Department of Diagnostic and Interventional Radiology, University Hospital Tuebingen, Tuebingen, Germany; Section of Experimental Radiology, University Hospital Tuebingen, Tuebingen, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Grosse
authors.forename: Fabian
authors.initials: F
authors.lastname: Springer
authors.forename: Tobias
authors.initials: T
authors.lastname: Hein
authors.forename: Gerd
authors.initials: G
authors.lastname: Grözinger
authors.forename: Christoph
authors.initials: C
authors.lastname: Schabel
authors.forename: Petros
authors.initials: P
authors.lastname: Martirosian
authors.forename: Fritz
authors.initials: F
authors.lastname: Schick
authors.forename: Roland
authors.initials: R
authors.lastname: Syha
mesh_terms: D000125:Achilles Tendon / Q000000981:diagnostic imaging / Q000502:physiology*; D000328:Adult; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D012016:Reference Values; D015203:Reproducibility of Results; D012420:Running / Q000502:physiology*; D014463:Ultrasonography
keywords: Achilles tendon; UTE imaging; relaxometry; tendinopathy