Method and apparatus using lateral access to obtain acoustoelastic extraction of axial material properties

1. An ultrasound system for measuring axial material properties of material using ultrasound, the ultrasound system comprising:

an ultrasound transducer assembly providing at least one ultrasonic transducer for:

(a) transmitting an ultrasound signal into the material along a first transverse direction perpendicular to an axial extent of the material and receiving the ultrasound signal after reflection and modification by the material to obtain a first and second echo signal from a first and second material location when the material is at a first and second tension applied along the axial extent of the material; and

(b) transmitting an ultrasound signal into the material along a first oblique direction at an angle between the transverse direction and the axial extent of the material and receiving the ultrasound signal after reflection and modification by the material to obtain a first and second echo signal from the first and second material location when the material is at the first and second tension applied along the axial extent; and

a processor receiving the first and second echo signal from the ultrasound signal along the transverse and oblique directions and processing the signals according to a stored program to determine at least one of axial stress and axial stiffness of the material.

2. The ultrasound system of claim 1 wherein the processor determines transverse material properties from the first and second echo signals from the ultrasonic signal along the transverse direction and determines axial properties from the transverse properties by analysis of a time of flight of the ultrasound along the transverse and oblique directions and a known geometry of a path of the ultrasound along the transverse and oblique directions.

3. The ultrasound system of claim 1 wherein the processor determines the transverse material properties from a time of flight of ultrasound between the first and second material positions and a reflection coefficient indicating reflected ultrasonic energy at the first and second material positions.

4. The ultrasound system of claim 3 where in the reflection coefficient is a measure of a relative power reflected at the material positions in a predetermined frequency range.

5. The ultrasound system of claim 1 wherein the processor determines axial stress in the material.

6. The ultrasound system of claim 1 wherein the processor determines axial stiffness of the material.

7. The ultrasound system of claim 1 wherein the ultrasonic transducer assembly includes three ultrasonic transducers fitting within a housing having surfaces to align the housing with respect to an axial direction of the material wherein the first ultrasonic transducer directs ultrasonic energy substantially perpendicular to the tissue when the housing is aligned with the tissue and the second and third ultrasonic transducers direct energy at complementary obtuse and acute angles with respect to a perpendicular to the axial direction when the housing is aligned with the axial direction.

8. The ultrasound system of claim 1 wherein the material is surrounded by a transmission material and the first and second material positions are interfaces between the material and the transmission material.

9. The ultrasound system of claim 8 wherein the transmission material is an elastomer of known material properties.

10. The ultrasound system of claim 1 wherein the material is selected from the group consisting of ligaments and tendons.

11. The ultrasound system of claim 1 wherein the ultrasound transducer assembly further provides at least one ultrasonic transducer for transmitting an ultrasound signal into the material along a second oblique direction at an angle between the transverse direction and a second axial extent of the material at an angle to the axial extent but within a plane with the axis extent perpendicular to the transverse direction, and receiving the ultrasound signal after reflection and modification by the material along the second oblique direction to obtain a first and second echo signal from the first and second material location when the material is at the first and second tension applied along the axial extent; and

wherein the processor receives the first and second echo signal from the ultrasound signal along the transverse and oblique directions and processing the signals according to a stored program to determine at least one of planar stress and planar stiffness of the material.

12. A method of measuring axial material properties of material using ultrasound, the method comprising:

using an ultrasound transducer assembly having at least one ultrasonic transducer to:

(a) transmit an ultrasound signal into the material along a first transverse direction perpendicular to an axial extent of the material and receiving the ultrasound signal after reflection and modification by the material to obtain a first and second echo signal from a first and second material location when the material is at a first and second tension applied along the axial extent of the material; and

(b) transmit an ultrasound signal into the material along a first oblique direction at an angle between the transverse direction and the axial extent of the material and receiving the ultrasound signal after reflection and modification by the material to obtain a first and second echo signal from the first and second material location when the material is at the first and second tension applied along the axial extent; and

(c) using an electronic processor executing a program stored in a non-transient medium for processing the first and second echo signals from the ultrasound signal along the transverse and oblique directions to determine at least one of axial stress and axial stiffness of the material.

13. The method of claim 12 wherein the transverse material properties are determined from the first and second echo signals from the ultrasonic signal along the transverse direction and the axial properties are determined from the transverse properties by analysis of a time of flight of the ultrasound and along the transverse and oblique directions and a known geometry of a path of the ultrasound along the transverse and oblique direction.

14. The method of claim 12 wherein the transverse material properties are determined from a time of flight of ultrasound between the first and second material positions and a reflection coefficient indicating reflected ultrasonic energy at the first and second material positions.

15. The method of claim 14 where in the reflection coefficient is a measure of a relative power reflected at the material positions in a predetermined frequency range.

16. The method of claim 12 wherein axial stress in the material is determined.

17. The method of claim 12 wherein axial stiffness of the material is determined.

18. The method of claim 12 wherein the material is surrounded by a transmission material and the first and second material positions are interfaces between the material and the transmission material.

19. The method of claim 18 wherein the transmission material is an elastomer of known material properties.

20. The method of claim 12 wherein the material is selected from the group consisting of ligaments and tendons.