Multi-beam tracking for angle error correction in speed of sound estimations

• US 4,878,500 A
• Filed: 07/13/1988
• Issued: 11/07/1989
• Est. Priority Date: 07/21/1986
• Status: Expired due to Term

• Current Assignee: University of Houston-University Park, Board of Regents of the University of Texas System (University of Texas System)
• Original Assignee: University of Houston-University Park, University of Texas System
• Inventors: Shattuck, David P., Ophir, Jonathan
• Primary Examiner(s): JAWORSKI, FRANCIS J
• Application Number:
  US07/218,810
• Time in Patent Office: 482 Days
• Field of Search: 128/660.01, 128/660.07, 73/597, 73/602
• US Class Current: 600/437
• CPC Class Codes: A61B 8/00 Diagnosis using ultrasonic, sonic or infrasonic waves imaging of objects using sonar G01S15/00
• CPC Class Codes: G01H 5/00 Measuring propagation velocity of ultrasonic, sonic or infrasonic waves , e.g. of pressure waves
• CPC Class Codes: G01S 15/8913 using separate transducers for transmission and reception
• CPC Class Codes: G01S 7/52025 for pulse systems G01S7/52034 takes precedence

Abstract

This invention relates to a method for correcting angle error present in in vivo sound velocity estimations. More particularly, this invention relates to a method for estimating the angle of misdirection of a tracked ultrasound beam used in sound velocity measurements in conjunction with multi-tracking ultrasound beams.

Claims

1. A method of correcting for angle error in sound velocity estimations in a target medium using ultrasound transducers comprising the steps of:

(a) applying a tracked ultrasound transducer oriented along an aiming axis to the outer surface of a target medium;

(b) applying a central tracking transducer oriented along an axis normal to the aiming axis of said tracked transducer to the outer surface of a target medium;

(c) applying a left and a right outer tracking transducer to the outer surface of a target medium, each of said outer tracking transducers placed on an opposite side of said central tracking transducer forming a tracking transducer axis with said central tracking transducer, said tracking transducer axis being parallel to said aiming axis and said left and right outer tracking transducers oriented at angles P and -P, respectively, from an axis normal to the aiming axis toward said central tracking transducer;

(d) employing a means for measuring the energy and travel time of signals produced by said ultrasound transducers;

(e) generating a tracked beam from said tracked ultrasound transducer which is misdirected at an angle T from said aiming axis;

(f) receiving ultrasound energy scattered from scatterers along said tracked beam to each of said tracking transducers;

(g) measuring the travel time required for ultrasound energy to travel from the tracked transducer to each of said tracking transducers;

(h) recording each of said measured travel times;

(i) relocating each of said tracking transducers a distance Δ

x from its present location in the same direction along said tracking transducer axis;

(j) repeating steps (d)-(i) to obtain a plurality of data sets for travel time at each location for each of said tracking transducers;

(k) plotting the plurality of data sets obtained in step (j) for each of said tracking transducers;

(l) fitting a line to each of the plots made in step (k);

(m) estimating the speed of sound along the tracked beam by calculating the slope of each of the fitted lines obtained in step (l);

(n) solving the following two equations, labeled (1) and (2), for the speed of sound, C;

##EQU8## where CE=the speed of sound obtained in step (m) for the central tracking transducer;

T=the angle of misdirection which the tracked beam undergoes in step (d);

P=the angle between the axis along which the left outer tracking transducers is aimed and an axis normal to the aiming axis;

CB=the speed of sound obtained in step (m) for one of said outer tracking transducers; and

CA=the speed of sound obtained in step (m) for the other outer tracking transducer.

2. The method of claim 1 wherein the plotting of the plurality of data sets obtained in step (j) for each of said tracking transducers is accomplished by plotting location on a vertical Y axis versus travel time on a horizontal X axis for each of said tracking transducers.

3. The method of claim 1 wherein the simultaneous solving of the two equations shown in step (n) is accomplished with a computer using an iterative numerical method.

4. The method of claim 1 wherein relocating each of said tracking transducers a distance Δ

x from its present location is accomplished by moving an attachment arm fastened to each of the tracking transducers a distance Δ

x.

5. A method for calculating the in vivo sound velocity in a target medium using multiple ultrasound transducers comprising the steps of:

(a) applying a tracked ultrasound transducer oriented along an aiming axis to the outer surface of a target medium;

(b) applying a central tracking transducer oriented along an axis normal to the aiming axis of said tracked transducer to the outer surface of a target medium;

(c) applying a right outer tracking transducer on the right side of said central tracking transducer, said right tracking transducer and said central tracking transducer forming a tracking transducer axis parallel to said aiming axis, said right tracking transducer being oriented at an angle -P toward said central tracking transducer from an axis normal to the aiming axis;

(d) applying a left outer tracking transducer on the left side of said central tracking transducer, said left outer tracking transducer, said right outer tracking transducer and said central tracking transducer forming a tracking transducer axis parallel to said aiming axis, said left tracking transducer being oriented at an angle P toward said central tracking transducer from an axis normal to tee aiming axis;

(e) connecting said tracked transducer and said tracking transducers electronically to an energy measuring and timing device;

(f) generating a tracked beam from said tracked ultrasound transducer which is misdirected at an angle T from said aiming axis;

(g) receiving ultrasound energy scattered from scatters along said tracked beam to each of said tracking transducers;

(h) recording the travel time required for ultrasound energy to travel from the tracked transducer to each of said tracking transducers;

(i) relocating each of said tracking transducers a distance Δ

x from its present location in the same direction along said tracking transducer axis;

(j) repeating steps (f)-(i) to obtain a plurality of data sets for travel time at each location for each of said tracking transducers;

(k) determining the functional relationship between travel time and location from the plurality of data sets obtained for each of said tracking transducers in step (j);

(l) estimating the speed of sound along the tracked beam from the functional relationship obtained in step (k) for each of said tracking transducers;

(m) solving the following two equations, labeled (1) and (2), for the speed of sound, C;

##EQU9## where CE=the speed of sound obtained in step (m) for the central tracking transducer;

T=the angle of misdirection which the tracked beam undergoes in step (d);

P=the angle between the axis along which the left outer tracking transducer is aimed and an axis normal to the aiming axis;

CB=the speed of sound obtained in step (l) for said right outer tracking transducer; and

CA=the speed of sound obtained in step (l) for said right outer tracking transducer.

6. The method of claim 5 wherein said tracked transducer and said tracking transducers are connected electronically to a computer.

7. The method of claim 5 wherein determining the functional relationship between travel time and location from the plurality of data sets obtained for each of the tracking transducers is accomplished by fitting a line to the data sets using a linear regression technique.

8. The method of claim 5 wherein said recording the travel time required for ultrasound energy to travel from the tracked transducer to each of the tracking transducers is accomplished for each tracking transducer by selecting a switch position on a switch electronically coupled to each of said tracking transducers and the pulse recording apparatus.

9. A method for calculating the in vivo sound velocity in a target medium using multiple ultrasound transducers comprising the steps of:

(a) applying a tracked transducer oriented along an aiming axis to the outer surface of a target medium;

(b) applying a multiplicity of tracking transducers aligned along a tracking transducer axis which is parallel to the aiming axis;

(c) electronically coupling each of said tracking transducers to a switch mechanism;

(d) electronically coupling the switch mechanism to a measuring and timing device;

(e) manipulating the switch mechanism to selectively couple three groups of tracking transducers to the measuring and timing device, said groups comprising a left outer tracking transducer oriented at an angle P from an axis normal to the aiming axis, a central tracking transducer oriented along an axis normal to the aiming axis, and a right outer tracking transducer oriented at an angle -P from an axis normal to the aiming axis;

(f) generating a tracked beam from the tracked ultrasound transducer, said tracked beam being misdirected at an angle T from the aiming axis;

(g) receiving ultrasound energy scattered from scatterers along said tracked beam to each of the tracking transducer groups coupled to the measuring and timing device;

(h) recording the travel time required for ultrasound energy to travel from the tracked transducer to each of the tracking transducer groups coupled to the measuring and timing device;

(i) manipulating the switch mechanism such that the measuring and timing device is coupled to three new groups of tracking transducers, each of said new groups of tracking transducers having shifted a distance Δ

x in the direction of translation from the position of the group of tracking transducers to which the measuring and timing device was coupled before the switch manipulation;

(j) repeating steps (f)-(i) to obtain a plurality of data sets for travel time at each location for each of the tracking transducer groups;

(k) determining the functional relationship between travel time and location from the plurality of data sets obtained for each of said tracking transducers in step (j);

(l) estimating the speed of sound along the tracked beam from the functional relationship obtained in step (k) for each of said tracking transducers;

(m) solving the following two equations, labeled (1) and (2), for the speed of sound, C;

##EQU10## where CE=the speed of sound obtained in step (m) for the central tracking transducer;

T=the angle of misdirection which the tracked beam undergoes in step (d);

P=the angle between the axis along which the left outer tracking transducer is aimed and an axis normal to the aiming axis;

CB=the speed of sound obtained in step (l) for said right outer tracking transducer; and

CA=the speed of sound obtained in step (l) for said right outer tracking transducer.

10. The method of claim 9 wherein each tracking transducer group comprises a single tracking transducer.

11. The method of claim 9 wherein each tracking transducer group comprises a phased array made up of a multiplicity of transducer elements.

12. The method of claim 9 wherein the multiplicity of tracking transducers are electronically coupled to a switch mechanism via a multiplexing module.

13. The method of claim 11 wherein phased array circuitry is used to orient the right and left outer tracking transducers at angles -P and P, respectively.

14. A method for calculating the in vivo sound velocity in a target medium using multiple ultrasound transducer elements comprising the steps of:

(a) applying a multiplicity of tracked ultrasound transducer elements oriented along an aiming axis to the outer surface of the target medium;

(b) applying a multiplicity of tracking transducer elements aligned along a tracking transducer axis which is parallel to the aiming axis;

(c) electronically coupling each of said tracked transducer elements to a first multiplexing module;

(d) electronically coupling each of said tracking transducer elements to a second multiplexing module;

(e) electronically coupling the first multiplexing module to at least one tracked transducer switch module;

(f) electronically coupling the second multiplexing module to three switch modules, said three switch modules to be known as the left switch module, the central switch module, and the right switch module;

(g) electronically coupling a beam forming and steering network to each of said switch modules;

(h) electronically coupling each beam forming and steering network to a computer.

(i) manipulating the central switch module such that a central group of tracking transducer elements operated in phased array are electronically coupled to the beam forming and steering network which is electronically coupled to the central switch module;

(j) manipulating the right switch module such that a group of transducer elements located to the right of the group of transducer elements electronically coupled to the central switch module are operated in phased array and electronically coupled to the beam forming and steering network which is electronically coupled to the right switch module;

(k) manipulating the left switch module such that a group of transducer elements located to the left of the group of transducer elements electronically coupled to the central switch module are operated in phased array and electronically coupled to the beam forming and steering network which is electronically coupled to the left switch module;

(l) operating the beam forming and steering network coupled to the left switch module such that the transducer elements operated in phased array and coupled to the left switch module transmit and receive ultrasound energy oriented at an angle P from an axis normal to the aiming axis;

(m) operating the beam forming and steering network coupled to the right switch module such that the transducer elements operated in phased array and coupled to the right switch module transmit and receive ultrasound energy oriented at an angle -P from an axis normal to the aiming axis;

(n) operating the beam forming and steering network coupled to the central switch module such that the transducer elements operated in phased array and coupled to the central switch module transmit and receive ultrasound energy oriented at an angle normal to the aiming axis;

(o) generating a tracked beam via the beam forming and steering network electronically coupled to the tracked transducer switch module, said tracked beam being misdirected at an angle T from the aiming axis;

(p) receiving ultrasound energy scattered from scatterers along said tracked beam to each of the transducer elements operated in phased array coupled to the beam forming and steering networks;

(q) recording the travel time required for ultrasound energy to travel from the tracked transducer elements operated in phased array to each of the tracking transducer elements operated in phased array and coupled to the computer;

(r) manipulating the left switch module, the central switch module and the right switch module such that the computer and the beam forming and steering networks electronically coupled to each of said switch modules is now coupled to a new group of transducer elements which has shifted a distance Δ

x in the direction of translation;

(s) repeating steps (o)-(r) to obtain a plurality of data sets for travel time at each location for each of the tracking transducer element phased arrays;

(t) determining the functional relationship between travel and location from the plurality of data sets obtained for each of said tracking transducers in step (s);

(u) estimating the speed of sound along the tracked beam from the functional relationship obtain in step (t) for each of said tracking transducers;

(v) solving the following two equations, labeled (1) and (2) for the speed of sound, C;

##EQU11## where CE=the speed of sound obtained in step (m) for the central tracking transducer;

T=the angle of misdirection which the tracked beam undergoes in step (d);

P=the angle between the axis along which the left outer tracking transducer is aimed and an axis normal to the aiming axis;

CB=the speed of sound obtained in step (l) for said right outer tracking transducer; and

CA=the speed of sound obtained in step (l) for said right outer tracking transducer.

15. The method of claim 14 further comprising:

(a) manipulating the tracked transducer switch module such that the group of transducer elements operated in phased array which is electronically coupled to this switch module is translated a distance Δ

x in the direction of translation from its prior location;

(b) repeating steps (o)-(v) of claim 14 for the new tracked beam axis;

(c) repeating steps (a)-(b) for a multiplicity of tracked beam axes;

(d) calculating the average sound velocity from the sound velocity calculated for each tracked beam axis.