Non-invasive determination of mechanical characteristics in the body

Abstract

A non-invasive system and method for inducing vibrations in a selected element of the human body and detecting the nature of responses for determining mechanical characteristics of the element are provided. The method comprises the steps of: inducing multiple-frequency vibrations, including below 20 KHz, in a selected element of the body by use of a driver; determining parameters of the vibration exerted on the body by the driver; sensing variations of a dimension of the element of the body over time, including in response to the driver; correlating the variations with frequency components of operation of the driver below 20 KHz to determine corresponding frequency components of the variations; resolving the frequency components into components of vibration mode shape; and determining the mechanical characteristics of the element on the basis of the parameters of vibration exerted by the driver and of the components of vibration mode shape.

I claim: 
     
       1. An non-invasive system for inducing vibrations in a selected element of the human body and detecting the nature of responses for determining mechanical characteristics of said element, said system comprising: a drive means for inducing multiple-frequency vibrations, including below 20 KHz, in .[.a.]. .Iadd.the .Iaddend.selected element of the body,   means for determining parameters of the vibration exerted on the body by the driver means,     .Iadd.means for determining the frequency components of mechanical impedance of the body based on said parameters of vibration exerted by said driver means, .Iaddend. means for sensing variations of a dimension of said element of the body over time, including in response to said driver means,   means for correlating said variations with frequency components of .[.operation.]. .Iadd.at least one .Iaddend.of .Iadd.said parameters of vibration exerted by .Iaddend.said driver means below 20 KHz, in order to determine corresponding frequency components of said variations.   means for resolving said frequency components .Iadd.of said variations .Iaddend.into components of vibration mode shape, and   computer means for interpreting said parameters of vibration exerted by the driver means.Iadd., said frequency components of mechanical impedance, .Iaddend.and said components of vibration mode shape in a manner to determine said mechanical characteristics.     
     
     
       2. The system of claim 1 wherein said parameters of vibration exerted by the driver means include force. 
     
     
       3. The system of claim 1 wherein said parameters of vibration exerted by the driver means include velocity. 
     
     
       4. The system of claim 1 wherein one said mechanical characteristic determined is pressure. 
     
     
       5. The system of claim 1 wherein said system further comprises means for detecting change in said components of vibration mode shape due to pressure change of said element, said change being included by said computer indetermination of said mechanical characteristics of said element. 
     
     
       6. The system of claim 1 wherein said driver means is adapted to induce a vibration frequency that changes over time. 
     
     
       7. The system of claim 1 wherein said driver means is adapted to induce multiple vibration frequencies simultaneously. 
     
     
       8. The system of claim 1, 4 or 5 wherein said body element includes a wall, and further comprising: means for resolving said components of vibration mode shape for at least two modes, and   means for comparing said determined mechanical characteristics of said elements respectively determined on the basis of said components of vibration mode shape for at least two modes in a manner to provide an indication of element wall stiffness.   
     
     
       9. The system of claim 1, 4 or 5 wherein said means for sensing variations of a dimension of said element of the body comprises means for emitting and receiving ultrasound signals. 
     
     
       10. The system of claim 4 or 5 wherein a said mechanical characteristic determined is systemic arterial blood pressure and said body element is a segment of the arterial system. 
     
     
       11. The system of claim 1 or 5 wherein a said mechanical characteristic determined is the mechanical impedance of a body element and said body element is an entire organ. 
     
     
       12. The system of claim 4 or 5 wherein a said mechanical characteristic determined is intraocular pressure and said body element is an eyeball. 
     
     
       13. The system of claim 12 wherein said means for sensing variations of a dimension of said eyeball comprises a time-varying display adjustable for creating visual impressions representative of the response of the eyeball to the vibrational forces exerted by the driver means. 
     
     
       14. The system of claim 4 or 5 wherein a said mechanical characteristic determined is pulmonary blood pressure and said body element is a segment of the pulmonary arterial system. 
     
     
       15. The system of claim 1 comprising a further means for sensing a dimension of said element, said sensed dimension being included by said computer means in determination of said mechanical characteristics of said element. 
     
     
       16. The system of claim 15 wherein said means for sensing a dimension of said element comprises optical measuring equipment. 
     
     
       17. The system of claim 4 or 5 further comprising means for applying a known pressure to said element in a manner to permit calibration of the system. 
     
     
       18. The system of claim 17 wherein the pressure application means is a pressure cuff. 
     
     
       19. The system of claim 1 wherein said means for sensing variations of a dimension is further adapted for sensing a dimension of said element, said sensed dimension being included by said computer means in determination of said mechanical characteristics of said element. 
     
     
       20. The system of claim 19 wherein said means for sensing a dimension of said element comprises equipment for emitting and receiving ultrasound signals. 
     
     
       21. A method for inducing vibrations in a selected element of the human body and detecting the nature of responses for determining mechanical characteristics of said element non-invasively, said method comprising the steps of: inducing multiple-frequency vibrations, including below 20 KHz, in .[.a.]. .Iadd.the .Iaddend.selected element of the body by use of a driver means,   determining parameters of the vibration exerted on the body by the driver means,     .Iadd.determining freuqency components of mechanical impedance of the body based on said parameters of vibration exerted by said driver means, .Iaddend. sensing variations of a dimension of said element of the body over time, including in response to said driver means,     correlating said variations with frequency components of .[.operation.]. .Iadd.at least one .Iaddend.of .Iadd.said parameters of vibration exerted by .Iaddend.said driver means below 20 KHz to determine corresponding frequency components of said variations,   resolving said frequency components .Iadd.of said variations .Iaddend.into components of vibration mode shape, and   interpreting said parameters of vibration exerted by the driver means.Iadd., said frequency components of mechanical impedance, .Iaddend.and said components of vibration mode shape in a manner to determine said mechanical characteristics of said element.   
     
     
       22. The method of claim 21 wherein said determination of parameters of vibration exerted by the driver means includes determining force. 
     
     
       23. The method of claim 21 wherein said determination of parameters of vibration exerted by the driver means includes determining velocity. 
     
     
       24. The method of claim 21 wherein a mechanical characteristic determined is pressure. 
     
     
       25. The method of claim 21 further comprising the step of detecting change in components of vibration mode shape due to pressure change of said element, said change being included in determination of said mechanical characteristics of said element. 
     
     
       26. The method of claim 21 wherein said multiple-frequency vibrations are generated by changing the operation frequency of the driver means over time. 
     
     
       27. The method of claim 21 wherein said multiple-frequency vibrations are generated by operation of the driver means at multiple frequencies simultaneously. 
     
     
       28. The method of claim 21, 24 or 25 wherein said body element includes a wall, and further comprising the steps of: resolving said components of vibration mode shape for at least two modes, and   comparing said determined mechanical characteristics of said elements respectively determined on the basis of said components of vibration mode shape for at least two modes in a manner to provide an indication of element wall stiffness.   
     
     
       29. The method of claim 21, 24 or 25 comprising sensing said variations of a dimension of said element of the body by means of ultrasound echo signals. 
     
     
       30. The method of claim 24 or 25 wherein a said mechanical characteristic determined is systemic arterial blood pressure and said body element is a segment of the arterial system. 
     
     
       31. The method of claim 21 or 25 wherein a said mechanical characteristic determined is the mechanical impedance of a body element and said body element is an entire organ. 
     
     
       32. The method of claim 24 or 25 wherein a said mechanical characteristic determined is intraocular pressure and said body element is an eyeball. 
     
     
       33. The method of claim 32 wherein said step of sensing variations of dimension comprises sensing variations of a dimension of said eyeball, and said method further comprises incorporating user feedback in response to visual impressions of a time-varying display, said visual impressions being representative of the response of the eyeball induced by the driver means. 
     
     
       34. The method of claim 24 or 25 wherein a said mechanical characteristic determined is pulmonary blood pressure and said body element is a segment of the pulmonary arterial system. 
     
     
       35. The method of claim 21, in addition to the step of sensing variations of a dimension of said element, said method further comprises sensing a dimension of said element, said sensed dimension being included in determination of said mechanical characteristics of said element. 
     
     
       36. The method of claim 35 wherein said dimension of said element is sensed by interpreting ultrasound echo signals. 
     
     
       37. The method of claim 35 wherein said dimension of said element is sensed optically. 
     
     
       38. The method of claim 24 or 25 further comprising applying a known pressure to said element in a manner to permit calibration. 
     
     
       39. The method of claim 38 further comprising applying said known pressure by means of a pressure cuff. .Iadd. 
     
     
       40.  A non-invasive system for inducing vibrations in a selected element of the human body and detecting the nature of responses for determining mechanical characteristics of said element, said system comprising: a driver means for inducing multiple-frequency vibrations, including below 20 KHz, in the selected element of the body,   means for determining parameters of the vibration exerted on the body by the driver means,     means for determining frequency components of mechanical impedance of the body based on said parameters of vibration exerted by said driver means, means for determining a dimension of the selected element of the body, and   computer means for interpreting said frequency components of mechanical impedance and said determined dimension in a manner to determine said mechanical characteristics. .Iaddend. .Iadd.     
     
     
       41.  A method for inducing vibrations in a selected element of the human body and detecting the nature of responses for determining mechanical characteristics of said element non-invasively, said method comprising the steps of: inducing multiple-frequency vibrations, including below 20 KHz, in the selected element of the body by use of a driver means,   determining parameters of the vibration exerted on the body by the driver means,   determining frequency components of mechanical impedance of the body based on said parameters of vibration exerted by said driver means,   determining a dimension of the selected element of the body, and   interpreting said frequency components of mechanical impedance and said determined dimension in a manner to determine said mechanical characteristics of said element. .Iaddend. .Iadd.     
     
     
       42.  In a non-invasive system for determining characteristics of an entire organ in a human body using an ultrasound beam, apparatus for aligning said beam with respect to said entire organ in two axes, comprising means for generating at least one magnetic field in response to a control signal,   an assembly adapted to rotate about said two axes in response to said at least one magnetic field, said assembly comprising an ultrasound component for steering said beam with respect to said two axes as said assembly rotates, and   means for producing said control signal as a function of the relative alignment of said beam with said entire organ to cause said beam to be steered with respect to said two axes and into alignment with said entire organ. .Iaddend. .Iadd.     
     
     
       43.  The system of claim 42 wherein said assembly further comprises a permanent magnet. .Iaddend. .Iadd.44. The system of claim 43 wherein said means for generating said at least one magnetic field comprises circuitry for generating a pair of magnetic fields to cause said permanent magnet to rotate independently with respect to each of said two axes. .Iaddend. .Iadd.45. The system of claim 42 wherein said ultrasound component 
     
     
        includes an electroacoustic ultrasound transducer. .Iaddend. .Iadd.46. The system of claim 42 wherein said apparatus for aligning further comprises means for coupling said ultrasound beam between said ultrasound 
     
     
        component and said entire organ. .Iaddend. .Iadd.47.  The system of claim 42 wherein said control signal is produced as a function of a measure of rotational response of said assembly in response to said at least one magnetic field. .Iaddend. .Iadd.48. The system of claim 47 wherein said rotational response is based at least in part on a model of response characteristics of said assembly to said at least one magnetic field. .Iaddend. .Iadd.49. The system of claim 48 wherein said model of response characteristics operates based on said control signal and does not require direct measurement of the rotational response of said assembly. .Iaddend. .Iadd.50. The system of claim 47 wherein said measure of rotational response is based on echo signals of said ultrasound beam. .Iaddend. .Iadd.51. The system of claim 42 wherein said control signal is servo-controlled based on echo signals of said ultrasound beam. .Iaddend. .Iadd.52. The system of claim 42 further comprising means for varying said alignment to scan said ultrasound beam over an angular sector. .Iaddend. 
     
     
        .Iadd.53.  The systtem of claim 52 wherein said angular sector is two-dimensional and said beam has a predetermined depth range, whereby said scanning permits features in a volume of said entire organ to be 
     
     
        mapped. .Iaddend. .Iadd.54.  The system of claim 1 wherein said body element is an entire organ and said means for emitting and receiving ultrasound signals includes apparatus for aligning said beam with said entire organ. .Iaddend.