title: Intradiurnal Fluctuations of Off-Resonance Saturation Effects in Healthy Human Achilles Tendons Assessed with a 3D Ultrashort Echo Time MRI Sequence at 3 Tesla.
abstract: OBJECTIVE
  The purpose of this study was to evaluate whether gravitational interstitial fluid accumulation in healthy subjects has an impact on off-resonance saturation ratios (OSR) or the volume of the Achilles tendon after a prolonged time of reduced levels of physical activity.
  
  
  METHODS
  7 healthy volunteers were repeatedly investigated on 3 consecutive days on a 3 T whole body MR scanner using an ultrashort echo time (UTE) imaging sequence with a Gaussian off-resonance saturation pulse at a frequency offset of 2000 Hz to calculate OSR values. For accurate volumetric quantification of the Achilles tendon, a newly developed contour detection snake algorithm was applied on high-resolution isotropic T2-weighted SPACE sequence datasets. Single-measure intraclass correlation coefficients (ICC) were calculated to estimate test-retest reliability.
  
  
  RESULTS
  For OSR and tendon volume measurements on three consecutive days, excellent reproducibility could be achieved with ICC values above 0.96 and 0.97, respectively. Comparing the results of all three days, a statistically significant mean individual percentage decrease (- 4.1  ± 1.5 %; p = 0.001) of calculated tendon OSR values was found for the evening measurements. No statistically significant difference between tendon volumes in the morning and the evening could be detected (p = 0.589).
  
  
  CONCLUSIONS
  The results of this in-vivo study demonstrate a significant influence of gravitational interstitial fluid accumulation after reduced physical activity on OSR values in the Achilles tendon, but not on tendon volume. Taken together with the demonstrated excellent reproducibility, these findings are important for future studies investigating temporal changes of the Achilles tendon microstructure.
authors.affiliation: Department of Diagnostic and Interventional Radiology, University Hospital Tuebingen, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Grosse
authors.affiliation: Department of Diagnostic and Interventional Radiology, University Hospital Tuebingen, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Syha
authors.affiliation: Department of Radiology, University Hospitals Case Medical Center, Case Western Reserve University, Cleveland, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Partovi
authors.affiliation: Department of Diagnostic and Interventional Radiology, University Hospital Tuebingen, Germany.
authors.forename: D E
authors.initials: DE
authors.lastname: Keßler
authors.affiliation: Department of Diagnostic and Interventional Radiology, University Hospital Tuebingen, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Bongers
authors.affiliation: Department of Diagnostic and Interventional Radiology, University Hospital Tuebingen, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Seith
authors.affiliation: Department of Diagnostic and Interventional Radiology, University Hospital Tuebingen, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Nikolaou
authors.affiliation: Department of Radiology, University Hospitals Case Medical Center, Case Western Reserve University, Cleveland, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Robbin
authors.affiliation: Section on Experimental Radiology, Department of Diagnostic and Interventional Radiology, University Hospital Tuebingen, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Schick
authors.affiliation: Department of Diagnostic and Interventional Radiology, University Hospital Tuebingen, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Springer
mesh_terms: D000125:Achilles Tendon / Q000033:anatomy & histology*; D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D045604:Extracellular Fluid / Q000502:physiology*; D005260:Female; D018495:Fluid Shifts / Q000502:physiology*; D006112:Gravitation; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009043:Motor Activity / Q000502:physiology; D016011:Normal Distribution; D009929:Organ Size / Q000502:physiology; D012016:Reference Values; D051598:Whole Body Imaging / Q000379:methods*