Ultrasonic transducer and examination method

• US 4,205,686 A
• Filed: 09/09/1977
• Issued: 06/03/1980
• Est. Priority Date: 09/09/1977
• Status: Expired due to Term

• Current Assignee: Picker Corp.
• Original Assignee: Picker Corp.
• Inventors: Harris, Daniel J., Bernardi, Richard B.
• Primary Examiner(s): Michell, Robert W.
• Assistant Examiner(s): Jaworski, Francis J.
• Application Number:
  US05/831,779
• Time in Patent Office: 998 Days
• Field of Search: 128/2 V, 128/2.05 Z, 128/24 A, 128/660-663, 73/632-633, 73/642, 73/644, 73/643, 310/328, 310/336-337, 310/367, 310/371
• US Class Current: 600/459
• CPC Class Codes: A61B 8/4281 characterised by sound-transmitting media or devices for coupling the transducer to the tissue
• CPC Class Codes: G01N 29/221 Arrangements for directing or focusing the acoustical waves electronic orientation or focusing G01N29/262; sound directing or focusing G10K11/26; mechanical steering of sound transducers or their beams G10K11/35
• CPC Class Codes: G10K 11/32 characterised by the shape of the source

Abstract

An ultrasonic system and method for examining the structure of a subject body is disclosed. The system includes an improved ultrasonic transducer and power circuitry for electrically stimulating the transducer to produce an incident ultrasonic energy beam along a path extending into the subject. The incident beam produces echoes within the subject, some of which propagate back toward the transducer. The transducer, in response to received echoes, produces electrical signals bearing information about the structure of the subject. The system further includes circuitry for processing the electrical signals and a display apparatus responsive to the processed electrical signals for producing a visual display of subject structure.

The transducer includes a concavo-convex piezoelectric emitter for producing ultrasonic energy having a dominant frequency, an acoustical impedance matching transformer and a coupling element. The impedance matching transformer includes a concavo-convex portion of material having a radius of curvature similar to that of the emitter, and being nested in contact with the emitter. The transformer has a uniform thickness equal to one-fourth of the wave length of the dominant ultrasonic frequency within the transformer. The characteristic acoustic impedance of the transformer material is approximately the geometric mean of the characteristic acoustic impedance of the emitter and the subject. The coupling element is made of material having acoustic characteristics similar to that of the subject body and is acoustically couplable between the impedance matching transformer and the subject surface, having a generally flat surface for contacting the subject.

Claims

1. An ultrasonic transducer assembly for an ultrasonic system for examining an animal body by propagating ultrasonic energy through the body, said assembly comprising:

(a) housing structure;

(b) an emitter including a concavo-convex portion of piezoelectric material having concave and convex faces and being disposed within the housing structure for emitting acoustical energy having a frequency distribution about a dominant frequency in response to electrical stimulation of the emitter;

(c) damping material adjacent the convex emitter face;

(d) an impedance transformer including a portion of material having a concavo-convex curvature substantially matching that of said emitter and being nested adjacent the concave emitter face, said portion having a substantially uniform thickness of approximately one-fourth of a wave length of acoustical energy of said dominant frequency propagating through the portion, and

(e) coupling structure including a portion of solid tissue equivalent material having acoustical characteristics similar to those of the tissue of the examined animal body, said coupling structure having a convex face disposed adjacent the concave side of the impedance transformer opposite the emitter and having a generally flat face opposite its said convex face for efficiently contacting substantially flat portions of the animal body.

2. The ultrasonic transducer assembly of claim 1, wherein said coupling structure has a characteristic acoustical impedance similar to that of tissue of the subject animal body.

3. The ultrasonic transducer assembly of claim 1, wherein said coupling structure is made of elastomeric polyurethane.

4. The ultrasonic transducer assembly of claim 1, wherein said impedance transformer is constructed of an epoxy material.

5. The ultrasonic transducer assembly of claim 1, wherein said emitter comprises a portion of lead zirconate titanate ceramic material.

6. The ultrasonic transducer assembly of claim 1, further comprising:

electrically conductive structure connected to said emitter for facilitating its electrical stimulation.

7. An ultrasonic system for examining structure of a subject, said system comprising:

(a) a display apparatus for producing a visual image representing such structure;

(b) processing circuitry responsive to electrical signals for actuating the display apparatus;

(c) power actuation circuitry;

(d) an ultrasonic transducer comprising;

(i) housing structure;

(ii) a focusing emitter having a concavo-convex configuration responsive to actuation from the power actuation circuitry for producing ultrasonic energy having a dominant frequency;

(iii) damping material adjacent a convex face of the emitter;

(iv) an impedance transformer including a portion of material having a concavo-convex curvature similar to that of said emitter and nested adjacent a concave emitter face, said portion of material having a substantially uniform thickness over a substantial area of said material of approximately one-quarter of a wave length of acoustical energy of the dominant frequency within the transformer, and

(v) said emitter having a first characteristic acoustic impedance, and said transformer having a characteristic acoustic impedance of approximately the geometric mean of said first characteristic impedance and characteristic acoustic impedance of the subject, and

(vi) a portion of solid material having acoustical characteristics similar to that of the subject being examined, said solid material having convex face nested substantially adjacent the concave face of the impedance transformer and a substantially flat face opposite the convex face for facilitating acoustical contact with a substantially flat portion of the subject being examined.

8. An acoustical energy transducer assembly for examining a subject, the transducer assembly comprising:

(a) a curved concavo-convex emitter having a characteristic acoustic impedance and being responsive to the application of electrical energy thereto to emit substantially focused acoustical energy having a dominant frequency;

(b) a concavo-convex acoustical impedance transformer disposed in a path of said acoustical energy, said acoustical impedance transformer having a uniform thickness substantially equal to an odd multiple of one-quarter of the wave length within the transformer of acoustical energy of the dominant frequency, said acoustical impedance transformer being disposed with its convex face substantially adjacent the concave face of the emitter, and

(c) a plano-convex portion of solid material having acoustical velocity and impedance approximately equal to that of animal tissue having a high water content, said portion being positioned with its convex face substantially adjacent the concave face of the transformer element.

9. The acoustical energy transducer assembly of claim 8, wherein:

said transformer is made of a material whose characteristic acoustic impedance is approximately the geometric mean of the characteristic acoustic impedances of the emitter and the subject.