Measurement of tissue elastic modulus

• US 8,167,804 B2
• Filed: 10/02/2007
• Issued: 05/01/2012
• Est. Priority Date: 10/03/2006
• Status: Active Grant

• Current Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Original Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Inventors: Kim, Kang, Weitzel, William F., Rubin, Jonathan M., Jia, Congxian, O'Donnell, Matthew, Kolias, Theodore J.
• Primary Examiner(s): Casler, Brian
• Assistant Examiner(s): Lamprecht, Joel
• Application Number:
  US11/866,000
• Publication Number:
  US 20080081994A1
• Time in Patent Office: 1,673 Days
• Field of Search: 600/407, 600437-448, 600/481, 600/480
• US Class Current: 600/438
• CPC Class Codes: A61B 5/0285 Measuring or recording phase velocity of blood waves
• CPC Class Codes: A61B 8/06 Measuring blood flow measuring volume flow in general G01F, e.g. G01F1/66, G01F1/72; measuring speed of fluids in general G01P5/00
• CPC Class Codes: A61B 8/08 Detecting organic movements or changes, e.g. tumours, cysts, swellings A61B8/02 - A61B8/06 take precedence
• CPC Class Codes: A61B 8/485 involving measuring strain or elastic properties
• CPC Class Codes: G01S 7/52036 using analysis of echo signal for target characterisation
• CPC Class Codes: G01S 7/52042 determining elastic properties of the propagation medium or of the reflective target diagnostic techniques involving the measurement of strain A61B8/485

Abstract

An optimized elastic modulus reconstruction procedure can estimate the nonlinear elastic properties of vascular wall from intramural strain and pulse wave velocity (PWV) measurements. A noninvasive free-hand ultrasound scanning procedure is used to apply external force, comparable to the force in measuring a subject'"'"'s blood pressure, to achieve higher strains by equalizing the internal arterial baseline pressure. PWV is estimated at the same location where intramural strain is measured. The reconstructed elastic modulus is optimized and the arterial elastic modulus can be determined and monitored using a simple dual elastic modulus reconstruction procedure.

Claims

1. A method of monitoring vascular wall compliance comprising:

measuring pulse wave velocity of the vascular wall over two or more mechanical loads from systolic pressure to equalized pressure;

measuring intramural strain of the vascular wall over two or more mechanical loads from systolic pressure to equalized pressure; and

reconstructing an elastic modulus for the vascular wall using the intramural strain and pulse wave velocity;

wherein the steps of measuring pulse wave velocity and measuring intramural strain each utilize an ultrasound probe and measuring pulse wave velocity comprises estimating the pulse wave velocity from a time delay between two ultrasound beams separated by a known distance.

2. The method of monitoring vascular wall compliance according to claim 1, wherein measuring pulse wave velocity includes rotating the ultrasound probe about 90 degrees relative to measuring intramural strain.

3. The method of monitoring vascular wall compliance according to claim 1, wherein measuring pulse wave velocity includes longitudinal ultrasound scanning of the vascular wall.

4. The method of monitoring vascular wall compliance according to claim 3, wherein the longitudinal ultrasound scanning spans from about 1 centimeter to about 10 centimeters.

5. The method of monitoring vascular wall compliance according to claim 1, wherein the time delay is based on a first arrival part of an ultrasound wave.

6. The method of monitoring vascular wall compliance according to claim 1, wherein the time delay is determined using speckle tracking to trace a frame-to-frame intramural wall displacement on each ultrasound beam.

7. The method of monitoring vascular wall compliance according to claim 3, wherein longitudinal ultrasound scanning of the vascular wall includes a plurality of measurements.

8. The method of monitoring vascular wall compliance according to claim 1, wherein measuring intramural strain includes transverse ultrasound scanning of the vascular wall.

9. The method of monitoring vascular wall compliance according to claim 1, wherein measuring intramural strain includes using phase-sensitive, two-dimensional speckle-tracking to determine intramural displacement and strain.

10. The method of monitoring vascular wall compliance according to claim 1, wherein reconstructing an elastic modulus for the vascular wall using the intramural strain and pulse wave velocity includes:

measuring an inner radius of the vascular wall;

determining an outer radius using the pulse wave velocity and the inner radius; and

ascertaining the elastic modulus of the vascular wall based on;

(a) the inner and outer radii, pulse pressure, and inter-cardiac strain, or

(b) the inner and outer radii and the density of the vascular wall.

18. The method of monitoring vascular wall compliance according to claim 1, further comprising measuring blood pressure.

11. A system for determining the vascular health of a patient comprising:

means for measuring pulse wave velocity of a vascular wall over two or more mechanical loads from systolic pressure to equalized pressure, wherein the means for measuring pulse wave velocity includes means for estimating the pulse wave velocity from a time delay between two ultrasound beams;

means for measuring intramural strain of the vascular wall over two or more mechanical loads from systolic pressure to equalized pressure;

means for reconstructing an elastic modulus of the vascular wall using the intramural strain and pulse wave velocity measurements; and

means for comparing the reconstructed elastic modulus to the elastic moduli of diseased and healthy vascular wall.

12. The system for determining the vascular health of a patient according to claim 11, wherein means for measuring intramural strain includes means for transverse ultrasound scanning of the vascular wall.

13. A method for locating a vascular wall lesion comprising:

measuring pulse wave velocity by longitudinal ultrasound scanning of the vascular wall over two or more mechanical loads from systolic pressure to equalized pressure, the longitudinal ultrasound scanning having proximal and distal ends, and estimating the pulse wave velocity from a time delay between two ultrasound beams separated by a known distance; and

locating the vascular wall lesion by comparing the pulse wave velocity at proximal and distal ends of the longitudinal scan.

14. The method for locating a vascular wall lesion according to claim 13, wherein measuring pulse wave velocity by longitudinal ultrasound scanning of the vascular wall includes measuring pulse wave velocity at a plurality of points along the longitudinal axis.

15. The method for locating a vascular wall lesion according to claim 13, wherein the longitudinal ultrasound scanning spans from about 1 centimeter to about 10 centimeters.

16. The method for locating a vascular wall lesion according to claim 13, wherein the time delay is based on a first arrival part of an ultrasound wave.

17. The method for locating a vascular wall lesion according to claim 13, wherein the time delay is determined using speckle tracking to trace a frame-to-frame intramural wall displacement on each ultrasound beam.