title: Continuous Shear Wave Elastography: A New Method to Measure Viscoelastic Properties of Tendons in Vivo.
abstract: Viscoelastic mechanical properties are frequently altered after tendon injuries and during recovery. Therefore, non-invasive measurements of shear viscoelastic properties may help evaluate tendon recovery and compare the effectiveness of different therapies. The objectives of this study were to describe an elastography method for measuring localized viscoelastic properties of tendons and to discuss the initial results in healthy and injured human Achilles and semitendinosus tendons. The technique used an external actuator to generate the shear waves in the tendon at different frequencies and plane wave imaging to measure shear wave displacements. For each of the excitation frequencies, maps of direction-specific wave speeds were calculated using local frequency estimation. Maps of viscoelastic properties were obtained using a pixel-wise curve fit of wave speed and frequency. The method was validated by comparing measurements of wave speed in agarose gels with those obtained using magnetic resonance elastography. Measurements in human healthy Achilles tendons revealed a pronounced increase in wave speed as a function of frequency, which highlights the importance of tendon viscoelasticity. Additionally, the viscoelastic properties of the Achilles tendon were larger than those reported for other tissues. Measurements in a tendinopathic Achilles tendon indicated that it is feasible to quantify local viscoelastic properties. Similarly, measurement in the semitendinosus tendon revealed substantial differences in viscoelastic properties between the healthy and contralateral tendons. Consequently, this technique has the potential to evaluate localized changes in tendon viscoelastic properties caused by injury and during recovery in a clinical setting.
authors: Biomedical Engineering Program, University of Delaware, Newark, Delaware, USA. Electronic address: Dhcortes@udel.edu.
authors: Daniel H
authors: DH
authors: Cortes
authors: Mechanical Engineering Department, University of Delaware, Newark, Delaware, USA.
authors: Stephen M
authors: SM
authors: Suydam
authors: Department of Physical Therapy, University of Delaware, Newark, Delaware, USA.
authors: Karin Grävare
authors: KG
authors: Silbernagel
authors: Mechanical Engineering Department, University of Delaware, Newark, Delaware, USA.
authors: Thomas S
authors: TS
authors: Buchanan
authors: Biomedical Engineering Program, University of Delaware, Newark, Delaware, USA.
authors: Dawn M
authors: DM
authors: Elliott
mesh_terms: D000125:Achilles Tendon / Q000000981:diagnostic imaging* / Q000503:physiopathology; D000293:Adolescent; D000328:Adult; D055119:Elastic Modulus / Q000502:physiology; D054459:Elasticity Imaging Techniques / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D013708:Tendon Injuries / Q000000981:diagnostic imaging* / Q000503:physiopathology; D014783:Viscosity; D055815:Young Adult
keywords: Achilles tendon; Biomarker; Elastography; Shear wave; Ultrasound