Method and apparatus for elastographic measurement and imaging

• US 5,178,147 A
• Filed: 05/10/1991
• Issued: 01/12/1993
• Est. Priority Date: 11/17/1989
• Status: Expired due to Term

• Current Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Original Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Inventors: Ponnekanti, Hari, Ophir, Jonathan, Cespedes, Ignacio
• Primary Examiner(s): JAWORSKI, FRANCIS J
• Application Number:
  US07/699,391
• Time in Patent Office: 613 Days
• Field of Search: 73/597, 73/599, 128/660.01, 128/660.07, 128/661.07, 128/661.03
• US Class Current: 600/437
• CPC Class Codes: A61B 5/0051 by applying vibrations
• CPC Class Codes: A61B 5/441 Skin evaluation, e.g. for skin disorder diagnosis
• CPC Class Codes: A61B 8/4272 involving the acoustic interface between the transducer and the tissue
• CPC Class Codes: G01N 2203/0089 Biorheological properties
• CPC Class Codes: G01N 2291/02827 Elastic parameters, strength or force
• CPC Class Codes: G01N 2291/101 one transducer
• CPC Class Codes: G01N 29/07 by measuring propagation velocity or propagation time of acoustic waves
• CPC Class Codes: G01N 29/223 Supports, positioning or alignment in fixed situation mounting transducers per se G10K11/004
• CPC Class Codes: G01N 29/30 Arrangements for calibrating or comparing, e.g. with standard objects
• CPC Class Codes: G01N 29/38 by time filtering, e.g. using time gates
• CPC Class Codes: G01N 29/50 using auto-correlation techniques or cross-correlation techniques
• CPC Class Codes: G01S 15/8945 using transducers mounted for linear mechanical movement
• 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 improved ultrasonic pulse-echo method and apparatus that has particular application in making precision measurements of compressibility in any backscattering material, in particular organic tissue, is disclosed. The method employs a standard transducer or transducer containing device which is translated transaxially, thereby compressing or displacing a proximal region of a target body in small known increments. At each increment, a pulse is emitted and an echo sequence (A-line) is detected from regions within the target along the sonic travel path or beam of the transducer. Resulting time shifts in echo segments corresponding to features in the target, corrected for regions of varying sonic speed along the sonic path, provide relative and quantitative information concerning the strain caused by the compressions. The stress imparted by the transducer and containing device is also determined, corrected for depth along the sonic path. The appropriate values for stress are divided into the respective values for strain along each path to yield an elastogram, or array of compressibility values, of the target.

Claims

1. A method of estimating compressibility of a target body, the method including the steps of:

(a) sonically coupling an ultrasonic source to said target body;

(b) emitting a first pulse of ultrasonic energy from the source along an axis in said target body;

(c) detecting the arrival time of a first echo sequence having at least one echo segment arriving in response to said first pulse of ultrasonic energy;

(d) transaxially moving the ultrasonic source so as to compress said target body;

(e) emitting a second pulse of ultrasonic energy from the source along said axis in the target body following said movement;

(f) detecting the arrival time of a second echo sequence having at least one echo segment, being congruent with at least one said echo segment having arrived in response to said first pulse, arriving in response to said second pulse of ultrasonic energy;

(g) measuring the differential displacement of a plurality of said congruent echo segments;

(h) calculating the strain along said axis following said movement;

(i) measuring the stress imparted along said axis as a result of said movement by;

(1) measuring the shape and area of the ultrasonic source, including any compressor attachments, compressing against the target body;

(2) determining a profile of variations in stress along said axis from the position along said axis and said shape and area of the source; and

(3) calculating a corrected stress along said axis by applying said profile to said measured stress; and

(j) dividing the strain along said axis by the stress along said axis.

2. The method of claim 1 wherein in steps (b) and (e) a plurality of said first and second pulses are emitted along a corresponding plurality of axes into the target body, and steps (c), (d), and (f) through (j) are performed for each said first and second pulses.

3. The method of claim 2 further comprising the steps of

(a) identifying regions along said axes having different sonic speeds from the determined values of compressibility;

(b) determining the time required for said pulses and echo sequences to traverse said regions along said axes;

(c) determining correction time delay factors for correcting variations in echo sequence travel time arising from variations in sonic speed in the target body; and

(d) applying said time delay factors to said echo sequences for correcting said substantial variations.