title: High variability in strain estimation errors when using a commercial ultrasound speckle tracking algorithm on tendon tissue.
abstract: BACKGROUND
  Ultrasound speckle tracking offers a non-invasive way of studying strain in the free Achilles tendon where no anatomical landmarks are available for tracking. This provides new possibilities for studying injury mechanisms during sport activity and the effects of shoes, orthotic devices, and rehabilitation protocols on tendon biomechanics.
  
  
  OBJECTIVE
  To investigate the feasibility of using a commercial ultrasound speckle tracking algorithm for assessing strain in tendon tissue.
  
  
  METHODS
  A polyvinyl alcohol (PVA) phantom, three porcine tendons, and a human Achilles tendon were mounted in a materials testing machine and loaded to 4% peak strain. Ultrasound long-axis cine-loops of the samples were recorded. Speckle tracking analysis of axial strain was performed using a commercial speckle tracking software. Estimated strain was then compared to reference strain known from the materials testing machine. Two frame rates and two region of interest (ROI) sizes were evaluated.
  
  
  RESULTS
  Best agreement between estimated strain and reference strain was found in the PVA phantom (absolute error in peak strain: 0.21 ± 0.08%). The absolute error in peak strain varied between 0.72 ± 0.65% and 10.64 ± 3.40% in the different tendon samples. Strain determined with a frame rate of 39.4 Hz had lower errors than 78.6 Hz as was the case with a 22 mm compared to an 11 mm ROI.
  
  
  CONCLUSIONS
  Errors in peak strain estimation showed high variability between tendon samples and were large in relation to strain levels previously described in the Achilles tendon.
authors.affiliation: Karolinska Institutet, Department of Clinical Sciences, Intervention and Technology (Clintec), Division of Orthopaedics and Biotechnology, Stockholm, Sweden asa.froberg@ki.se.
authors.forename: Åsa
authors.initials: Å
authors.lastname: Fröberg
authors.affiliation: School of Technology and Health, KTH Royal Institute of Technology, Huddinge, Sweden.
authors.forename: Mattias
authors.initials: M
authors.lastname: Mårtensson
authors.affiliation: School of Technology and Health, KTH Royal Institute of Technology, Huddinge, Sweden.
authors.forename: Matilda
authors.initials: M
authors.lastname: Larsson
authors.affiliation: School of Technology and Health, KTH Royal Institute of Technology, Huddinge, Sweden Karolinska Institutet, Department of Clinical Sciences, Intervention and Technology (Clintec), Division of Medical Imaging and Technology, Stockholm, Sweden.
authors.forename: Birgitta
authors.initials: B
authors.lastname: Janerot-Sjöberg
authors.affiliation: Cardiovascular Imaging and Dynamics, Department of Cardiovascular Sciences, KU Leuven, Leuven, Belgium.
authors.forename: Jan
authors.initials: J
authors.lastname: D'Hooge
authors.affiliation: Karolinska Institutet, Department of Clinical Sciences, Intervention and Technology (Clintec), Division of Orthopaedics and Biotechnology, Stockholm, Sweden The Swedish School of Sport and Health Sciences, Stockholm, Sweden.
authors.forename: Anton
authors.initials: A
authors.lastname: Arndt
mesh_terms: D000125:Achilles Tendon / Q000000981:diagnostic imaging* / Q000502:physiology*; D000465:Algorithms; D000818:Animals; D001696:Biomechanical Phenomena; D004867:Equipment Design; D006801:Humans; D066298:In Vitro Techniques; D019047:Phantoms, Imaging; D012984:Software; D013552:Swine; D014463:Ultrasonography / Q000379:methods*
keywords: Achilles tendon; Speckle tracking; strain; ultrasound