# US 2013/0253318 A1 · Method and apparatus for determining viscoelastic parameters in tissue > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2013/0253318 A1 - Document ID: US20130253318A1 - Status: Published application - Kind: A1 - Application number: 13/786,026 - Filed: 2013-03-05 - Published: 2013-09-26 - Earliest claimed: 2008-11-03 - Assignees: The University of British Columbia - Applicants: University of British Columbia - Inventors: Hani Eskandari; Septimiu E. Salcudean; Robert N. Rohling - Web page: https://patentgrep.com/patent/US20130253318A1 ## CPC - A61B 8/485: {involving measuring strain or elastic properties} - A61B 8/00: Diagnosis using ultrasonic, sonic or infrasonic waves - A61B 8/13: Tomography (A61B8/10, A61B8/12 take precedence) - A61B 8/587: {Calibration phantoms} - G01S 15/8977: {using special techniques for image reconstruction, e.g. FFT, geometrical transformations, spatial deconvolution, time deconvolution} - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) - G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES ## Abstract Described herein are a method and apparatus for determining viscoelastic parameters of a tissue. A vibration signal is applied to the tissue and displacements at a plurality of locations within the tissue are measured at a plurality of times. The viscoelastic parameters of the tissue, including elasticity and viscosity, can then be determined by fitting a finite element model of the tissue to the vibration signal and the measured displacements and by solving for the viscoelastic parameters of the model. A value for density of each element of the model is selected and the absolute values for the viscoelastic parameters of each of the elements in the model is determined. Alternatively, the difference in relaxation-times between two locations within the tissue can be determined from the difference in phases of the strains at the two locations. ## Claims ### Claim 1 A method for determining viscoelastic parameters of a tissue, the method comprising: (a) applying a vibration signal to the tissue; (b) measuring displacements at a plurality of locations within the tissue in response to the vibration signal at a plurality of times; and (c) determining the viscoelastic parameters of the tissue by fitting a finite element model of the tissue to the vibration signal and the measured displacements and solving for viscoelastic parameters of the model, wherein a value for density of each element of the model is selected and absolute values for one or more of the viscoelastic parameters for each of the elements of the model are solved. ### Claim 2 (depends on 1) A method as claimed in claim 1 wherein the measured displacements are expressed in a frequency domain as phasors having a real and an imaginary component. ### Claim 3 (depends on 1) A method as claimed in claim 1 wherein the viscoelastic parameters that are solved include both elasticity and viscosity. ### Claim 4 (depends on 1) A method as claimed in claim 1 wherein the value for density of each element is selected to be the density of water. ### Claim 5 (depends on 3) A method as claimed in claim 3 wherein the viscoelastic parameters further comprise one or more of relaxation-time and wave speed. ### Claim 6 (depends on 1) A method as claimed in claim 1 wherein the vibration signal consists of one frequency component. ### Claim 7 (depends on 1) A method as claimed in claim 1 wherein the solving for viscoelastic parameters comprises generating a system of equations comprising a viscosity and elasticity of each of the elements of the model and wherein the system of equations is treated as being linear in the viscosity and elasticity of each of the elements. ### Claim 8 (depends on 7) A method as claimed in claim 7 wherein the viscoelastic parameters are unconstrained. ### Claim 9 (depends on 7) A method as claimed in claim 7 wherein the viscoelastic parameters are constrained. ### Claim 10 (depends on 1) A method as claimed in claim 1 wherein the system of equations is solved iteratively by minimizing a cost function. ### Claim 11 (depends on 1) A method as claimed in claim 1 wherein the system of equations is solved using instrumental variables. ### Claim 12 (depends on 9) A method as claimed in claim 9 wherein the system of equations is solved iteratively by minimizing a cost function. ### Claim 13 (depends on 9) A method as claimed in claim 9 wherein the number of equations in the system of equations is reduced by removing equations from the system of equations for which non-zero force terms are present. ### Claim 14 (depends on 9) A method as claimed in claim 9 wherein the elasticity of each of the elements is constrained to be between 0 MPa and 1 MPa. ### Claim 15 (depends on 9) A method as claimed in claim 9 wherein the viscosity of each of the elements is constrained to be between 0 kPa·s and 1 kPa·s. ### Claim 16 (depends on 1) A method as claimed in claim 1 wherein the solving for viscoelastic parameters comprises generating a system of equations comprising a viscosity and elasticity of each of the elements of the model and wherein the system of equations is treated as being non-linear in the viscosity and elasticity of each of the elements. ### Claim 17 (depends on 16) A method as claimed in claim 16 wherein the system of equations is solved iteratively by minimizing a cost function. ### Claim at position 18 -24. (canceled) ### Claim 25 An apparatus for determining viscoelastic parameters of a tissue, the apparatus comprising: (a) an actuator for generating a vibration signal and applying a generated vibration signal to the tissue; (b) a driver circuit connected to drive the actuator to generate a vibration signal having at least one frequency component; (c) an ultrasound imaging system configured to measure displacements at a plurality of locations within the tissue in response to the vibration signal at a plurality of times; and (d) a data processor communicatively coupled to the ultrasound imaging system and configured to determine the viscoelastic parameters of the tissue including elasticity and viscosity by fitting a finite element model of the tissue to the vibration signal and the measured displacements and solving for viscoelastic parameters of the model, wherein a value for density of each element of the model is selected and absolute values for one or more of the viscoelastic parameters for each of the elements of the model are solved. ### Claim 26 (canceled)