title: A mechano-acoustic indentor system for in vivo measurement of nonlinear elastic properties of soft tissue.
abstract: OBJECTIVE
  Soft tissue exhibits nonlinear stress-strain behavior under compression. Characterizing its nonlinear elasticity may aid detection, diagnosis, and treatment of soft tissue abnormality. The purposes of this study were to develop a rate-controlled Mechano-Acoustic Indentor System and a corresponding finite element optimization method to extract nonlinear elastic parameters of soft tissue and evaluate its test-retest reliability.
  
  
  METHODS
  An indentor system using a linear actuator to drive a force-sensitive probe with a tip-mounted ultrasound transducer was developed. Twenty independent sites at the upper lateral quadrant of the buttock from 11 asymptomatic subjects (7 men and 4 women from a chiropractic college) were indented at 6% per second for 3 sessions, each consisting of 5 trials. Tissue thickness, force at 25% deformation, and area under the load-deformation curve from 0% to 25% deformation were calculated. Optimized hyperelastic parameters of the soft tissue were calculated with a finite element model using a first-order Ogden material model. Load-deformation response on a standardized block was then simulated, and the corresponding area and force parameters were calculated. Between-trials repeatability and test-retest reliability of each parameter were evaluated using coefficients of variation and intraclass correlation coefficients, respectively.
  
  
  RESULTS
  Load-deformation responses were highly reproducible under repeated measurements. Coefficients of variation of tissue thickness, area under the load-deformation curve from 0% to 25% deformation, and force at 25% deformation averaged 0.51%, 2.31%, and 2.23%, respectively. Intraclass correlation coefficients ranged between 0.959 and 0.999, indicating excellent test-retest reliability.
  
  
  CONCLUSIONS
  The automated Mechano-Acoustic Indentor System and its corresponding optimization technique offers a viable technology to make in vivo measurement of the nonlinear elastic properties of soft tissue. This technology showed excellent between-trials repeatability and test-retest reliability with potential to quantify the effects of a wide variety of manual therapy techniques on the soft tissue elastic properties.
authors: Director and Associate Professor, Foot Levelers Biomechanics Research Laboratory, Department of Research, New York Chiropractic College, Seneca Falls, USA. tkoo@nycc.edu
authors: Terry K
authors: TK
authors: Koo
authors: Jeffrey H
authors: JH
authors: Cohen
authors: Yongping
authors: Y
authors: Zheng
mesh_terms: D000162:Acoustics; D000328:Adult; D000465:Algorithms; D001696:Biomechanical Phenomena; D002081:Buttocks / Q000502:physiology*; D004548:Elasticity; D004867:Equipment Design; D005260:Female; D006801:Humans; D008297:Male; D010808:Physical Examination / Q000295:instrumentation* / Q000379:methods*