Nonlinear System Identification Techniques and Devices for Discovering Dynamic and Static Tissue Properties

• US 20110054354A1
• Filed: 08/31/2010
• Published: 03/03/2011
• Est. Priority Date: 09/01/2009
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Hunter, Ian W., Chen, Yi
• Granted Patent: US 8,758,271 B2
• Time in Patent Office: Days
• US Class Current: 600/587
• CPC Class Codes: A01G 7/00 Botany in general
• CPC Class Codes: A61B 5/0048 Detecting, measuring or recording by applying mechanical forces or stimuli A61B5/021, A61B5/4884 and A61B9/00 take precedence
• CPC Class Codes: A61B 5/0053 by applying pressure, e.g. compression, indentation, palpation, grasping, gauging
• CPC Class Codes: A61B 5/0055 by applying suction
• CPC Class Codes: A61B 5/0057 by applying motion other than vibrations, e.g. rolling, rubbing, applying a torque, tribometry
• CPC Class Codes: A61B 5/103 Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes A61B5/08 takes precedence; measuring aids for tailors A41H1/00; measuring instruments specially adapted for dentistry A61C19/04
• CPC Class Codes: A61B 5/442 Evaluating skin mechanical properties, e.g. elasticity, hardness, texture, wrinkle assessment
• CPC Class Codes: A61B 5/6824 Arm or wrist
• CPC Class Codes: A61B 9/00 Instruments for examination by percussion; Pleximeters
• CPC Class Codes: G01N 2203/0069 Fatigue, creep, strain-stress relations or elastic constants
• CPC Class Codes: G01N 2203/0218 Calculations based on experimental data
• CPC Class Codes: G01N 2203/0246 Special simulation of "in situ" conditions, scale models or dummies
• CPC Class Codes: G01N 2203/0278 Thin specimens
• CPC Class Codes: G01N 3/24 by applying steady shearing forces G01N3/26, G01N3/28 take precedence
• CPC Class Codes: G01N 3/40 Investigating hardness or rebound hardness

Abstract

A device for measuring a mechanical property of a tissue includes a probe configured to perturb the tissue with movement relative to a surface of the tissue, an actuator coupled to the probe to move the probe, a detector configured to measure a response of the tissue to the perturbation, and a controller coupled to the actuator and the detector. The controller drives the actuator using a stochastic sequence and determines the mechanical property of the tissue using the measured response received from the detector. The probe can be coupled to the tissue surface. The device can include a reference surface configured to contact the tissue surface. The probe may include a set of interchangeable heads, the set including a head for lateral movement of the probe and a head for perpendicular movement of the probe. The perturbation can include extension of the tissue with the probe or sliding the probe across the tissue surface and may also include indentation of the tissue with the probe. In some embodiments, the actuator includes a Lorentz force linear actuator. The mechanical property may be determined using non-linear stochastic system identification. The mechanical property may be indicative of, for example, tissue compliance and tissue elasticity. The device can further include a handle for manual application of the probe to the surface of the tissue and may include an accelerometer detecting an orientation of the probe. The device can be used to test skin tissue of an animal, plant tissue, such as fruit and vegetables, or any other biological tissue.

Claims

1. A device for measuring a mechanical property of a tissue, the device comprising:

a probe configured to perturb the tissue with lateral movement relative to a surface of the tissue;

an actuator coupled to the probe to move the probe;

a detector configured to measure a response of the tissue to the perturbation; and

a controller coupled to the actuator and the detector, the controller driving the actuator using a stochastic sequence and determining the mechanical property of the tissue using the measured response received from the detector.

2. The device of claim 1, wherein the probe is coupled to the tissue surface.

3. The device of claim 1, further comprising a reference surface configured to contact the tissue surface.

4. The device of claim 1, wherein the probe comprises a set of interchangeable heads, the set comprising a head for lateral movement of the probe and a head for perpendicular movement of the probe.

5. The device of claim 1, wherein the perturbation comprises extension of the tissue with the probe.

6. The device of claim 1, wherein the perturbation comprises sliding the probe across the tissue surface

7. The device of claim 1, wherein the actuator includes a Lorentz force linear actuator.

8. The device of claim 1, wherein the mechanical property is determined using non-linear stochastic system identification.

9. The device of claim 1, wherein the mechanical property is indicative of tissue compliance.

10. The device of claim 1, wherein the mechanical property is indicative of tissue elasticity.

11. The device of claim 1, wherein the detector comprises a force sensor detecting force of the perturbation.

12. The device of claim 11, wherein the force sensor comprises a current sensor detecting a current input to the actuator.

13. The device of claim 1, wherein the detector comprises a position sensor detecting displacement of the tissue surface.

14. The device of claim 1, further comprising a handle for manual application of the probe to the surface of the tissue.

15. The device of claim 14, further comprising an accelerometer detecting an orientation of the probe.

16. A method of measuring a mechanical property of tissue comprising:

placing a probe against a surface of the tissue;

mechanically perturbing the tissue with lateral movement of the probe using a stochastic sequence;

measuring a response of the tissue to the perturbation; and

determining a mechanical property of the tissue based on the measured response to the perturbation.

17. The method of claim 16, wherein placing the probe comprises coupling the probe to the tissue surface.

18. The method of claim 16, wherein perturbing the tissue comprises extending the tissue surface with the probe.

19. The method of claim 16, wherein perturbing the tissue comprises sliding the probe across the tissue surface.

20. The method of claim 16, wherein perturbing the tissue comprises using a Lorentz force linear actuator.

21. The method of claim 16, wherein determining comprises using non-linear stochastic system identification.

22. The method of claim 21, wherein determining further comprises modeling the probe and tissue as a system comprising a linear dynamic component and a non-linear static component.

23. The method of claim 22, wherein the non-linear component includes a Wiener static nonlinear system.

24. The method of claim 22, wherein the linear component includes a second order mechanical system.

25. The method of claim 21, wherein using non-linear stochastic system identification comprises using a Volterra Kernel method.

26. The method of claim 16, wherein the mechanical property is indicative of tissue compliance.

27. The method of claim 16, wherein the mechanical property is indicative of tissue elasticity.

28. The method of claim 16, wherein the tissue is skin tissue of an animal.

29. The method of claim 16, wherein the tissue is plant tissue.

30. The method of claim 16, further comprising detecting force of the perturbation with respect to a reference surface.

31. The method of claim 16, wherein measuring a response comprises detecting displacement of the tissue surface with respect to a reference surface.

32. A method of testing produce, the method comprising:

placing a probe against a skin of a piece of produce;

mechanically perturbing the piece of produce with the probe;

measuring a response of the piece of produce to the perturbation; and

analyzing the measured response using non-linear stochastic system identification.

33. The method of claim 32, wherein placing the probe comprises coupling the probe to the skin.

34. The method of claim 32, wherein perturbing the piece of produce comprises using a Lorentz force linear actuator.

35. The method of claim 32, wherein perturbing the piece of produce comprises using a stochastic sequence.

36. The method of claim 32, wherein perturbing the piece of produce comprises indenting the piece of produce with the probe.

37. The method of claim 32, wherein measuring a response comprises detecting displacement of the skin.

38. The method of claim 32, further comprising detecting force of the perturbation,

39. The method of claim 32, wherein the probe is manually placed against the skin by means of a handle coupled to the probe.

40. The method of claim 32, wherein analyzing comprises determining a mechanical property of the piece of produce.

41. The method of claim 32, wherein the mechanical property is indicative of ripeness.

42. A method of analyzing mechanical properties of tissue comprising:

mechanically perturbing the tissue using a stochastic input sequence;

measuring a response of the tissue to the perturbation;

partitioning the measured response; and

generating a representation of the mechanical properties of the tissue based on the partitioned response.

43. The method of claim 42, wherein perturbing the tissue comprises using a Lorentz force linear actuator.

44. The method of claim 42, wherein perturbing the tissue comprises indenting the tissue with a probe.

45. The method of claim 42, wherein perturbing the tissue comprises extending a tissue surface with a probe.

46. The method of claim 42, wherein perturbing the tissue comprises sliding a probe across a tissue surface.

47. The method of claim 42, wherein measuring a response comprises detecting position of the tissue.

48. The method of claim 47, wherein partitioning comprises grouping the measured response into position bins over which the measured response approximates a linear response to the perturbation.

49. The method of claim 48, wherein generating a representation comprises generating a time-domain representation of the partitioned response.

50. The method of claim 49, wherein generating a representation further comprises using orthogonalization of the input sequence based on the position bins.

51. The method of claim 50, wherein the time-domain representation includes an impulse response for each position bin.

52. A method of analyzing mechanical properties of tissue comprising:

mechanically perturbing the tissue with a probe using a stochastic input sequence;

measuring a response of the tissue to the perturbation;

analyzing the measured response; and

while perturbing, adjusting the input sequence based on the analysis.

53. The method of claim 52, wherein perturbing the tissue comprises using a Lorentz force linear actuator.

54. The method of claim 52, wherein measuring a response comprises detecting displacement of the tissue.

55. The method of claim 52, wherein analyzing comprises using non-linear stochastic system identification.

56. The method of claim 52, wherein analyzing comprises obtaining a distribution of the measured response.

57. The method of claim 52, wherein analyzing comprises determining a mechanical property of the tissue.

58. The method of claim 52, further comprising generating the stochastic input sequence.