title: Shear wave elastography using ultrasound: effects of anisotropy and stretch stress on a tissue phantom andin vivoreactive lymph nodes in the neck.
abstract: OBJECTIVE
  The purpose of this study was to evaluate how the anisotropy and the static stretch stress of the cervical musculature influence the measured shear modulus in a tissue-mimicking phantom and in cervical lymph nodesin vivoby using shear wave elastography (SWE).
  
  
  METHODS
  SWE was performed on a phantom using a pig muscle and on the middle jugular cervical lymph nodes in six volunteers. Tissue elasticity was quantified using the shear modulus and a supersonic shear wave imaging technique. For the phantom study, first, the optimal depth for measurement was determined, and then, SWE was performed in parallel and perpendicular to the muscle fiber orientation with and without strain stress. For thein vivostudy, SWE was performed on the cervical lymph nodes in parallel and perpendicular to the sternocleidomastoid muscle fiber direction with and without neck stretching. The mean values of the shear modulus (meanSM) were then analyzed.
  
  
  RESULTS
  In the phantom study, the measured depth significantly influenced the meanSM with a sharp decrease at the depth of 1.5 cm (P<0.001). Strain stress increased the meanSM, irrespective of the muscle fiber orientation (P<0.001). In thein vivostudy, the meanSM values obtained in parallel to the muscle fiber orientation were greater than those obtained perpendicular to the fiber orientation, irrespective of the stretch stress (P<0.001). However, meanSM was affected significantly by the stretch stress parallel to the muscle fiber orientation (P<0.001).
  
  
  CONCLUSIONS
  The anisotropic nature of the cervical musculature and the applied stretch stress explain the variability of the SWE measurements and should be identified before applying SWE for the interpretation of the measured shear modulus values.
authors.affiliation: Department of Radiology, University of Inha College of Medicine, Incheon, Korea.
authors.forename: Ha Young
authors.identifier: 0000-0003-2343-3434
authors.initials: HY
authors.lastname: Lee
authors.affiliation: Department of Radiology and Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Jeong Hyun
authors.identifier: 0000-0002-0021-4477
authors.initials: JH
authors.lastname: Lee
authors.affiliation: Department of Radiology and Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Ji Hoon
authors.identifier: 0000-0001-6598-9049
authors.initials: JH
authors.lastname: Shin
authors.affiliation: Department of Radiology and Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: So Yeon
authors.identifier: 0000-0001-6245-8867
authors.initials: SY
authors.lastname: Kim
authors.affiliation: Department of Radiology and Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Hee Jung
authors.identifier: 0000-0002-3398-1074
authors.initials: HJ
authors.lastname: Shin
authors.affiliation: Department of Radiology, Hanyang University College of Medicine, Seoul, Korea.
authors.forename: Jeong Seon
authors.identifier: 0000-0002-5550-6645
authors.initials: JS
authors.lastname: Park
authors.affiliation: Department of Radiology and Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Young Jun
authors.identifier: 0000-0001-7098-5042
authors.initials: YJ
authors.lastname: Choi
authors.affiliation: Department of Radiology and Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Jung Hwan
authors.identifier: 0000-0003-0480-4754
authors.initials: JH
authors.lastname: Baek
keywords: Anisotropy; Elasticity imaging techniques; Lymph nodes; Neck; Shear wave imaging