Ultrasonic imaging system utilizing dynamic and pseudo-dynamic focusing

• US 4,241,610 A
• Filed: 02/05/1979
• Issued: 12/30/1980
• Est. Priority Date: 02/05/1979
• Status: Expired due to Term

• Current Assignee: Diasonics Delaware Incorporated
• Original Assignee: Varian Associates, Inc. (Siemens AG)
• Inventors: Anderson, Weston A.
• Primary Examiner(s): Ciarlante, Anthony V.
• Application Number:
  US06/009,721
• Time in Patent Office: 694 Days
• Field of Search: 73/626, 73/625, 73/628, 128/660
• US Class Current: 73/626
• CPC Class Codes: G01S 15/8918 the array being linear
• CPC Class Codes: G01S 7/52046 Techniques for image enhancement involving transmitter or receiver image enhancement by image data processing G06T5/00

Abstract

A phased array ultrasonic imaging system is disclosed which combines aspects of both dynamic and pseudo-dynamic focusing. The system includes a linearly arranged array of side-by-side transducers adapted for propagating ultrasonic energy into a body to be ultrasonically examined and for receiving reradiated sonic energy from points within the body. A signal channel is connected to each of the transducers for activating same to propagate the sonic energy and for receiving electrical signals from the transducers (which correspond to the reradiated energy). Controllable delay means are provided in each of the channels for introducing linear phase shifts in the electrical signals proceeding in the channels during both transmission and reception to thereby azimuthally steer the transducer array. Means are further provided for processing the received signals proceeding through the channels and for combining same to effect a visual display of the bodily portion being examined. Means synchronized with the activating of the transmitters periodically reduce the gain of one or more symmetric outer transducer pairs of the array, thereby effecting reducing the aperture of the array to enable improved response to reflected acoustic information reaching the array from the near field thereof. The outer elements are similarly restored to enlarge the effective array aperture for improved response to reflected acoustic information arising from the far field of the array. Pursuant to the improvement of the invention, means are provided for adjusting the focal length of the array coincident with the aforementioned change in gain of the one or more outer transducer pairs, i.e., coincident with a change in effective aperture of the array in order to thereby maintain or achieve a desired resolution within a specified focal range.

Claims

1. In a phased array ultrasonic imaging system of the type comprising:

a linear array of side-by-side transducers adapted for propagating ultrasonic energy into a body to be ultrasonically examined and for receiving reradiated sonic energy from points within said body;

a signal channel connected to each of said transducers, for activating said transducers to propagate said sonic energy, and for receiving electrical signals from said transducers corresponding to said reradiated energy;

delay means in each of said channels for introducing time delays in the electrical signals proceeding in said channels during said transmission and reception;

means controlling said delay means in each of said channels thereby to steer the acoustic beam from said transducer array over a desired azimuthal range to enable scanning of said body;

means for processing the received signals proceeding through said channels, and for combining said signals and effecting a visual display of the bodily portion being examined; and

means synchronized with the activation of said transmitters for periodically reducing the gain of one or more symmetrically disposed outer pairs of elements of said array, to thereby reduce the effective aperture of said array for improved response to reflected acoustic information near said array and for restoring the gain of said transducer pairs, thereby increasing the said effective aperture of said array for improved response to reflected acoustic information reaching said array from the far field of the object being examined;

the improvement comprising;

means for adjusting the focal length of said array coincidental with the said changes of gain of said pair of elements of said array whereby to maintain a desired resolution within a desired focal range.

2. A system in accordance with claim 1 wherein said adjustmemt of said focal length is effected by further adjusting the delays in each of said channels coincident with said change in gain of said pair of elements, to thereby superimpose the resultant change in focus on the said phase shift producing azimuthal steering of said acoustic beam.

3. A system in accordance with claim 1, wherein said means adjusting said focal length effects a plurality of said adjustments in accordance with a plurality of changes in said effective aperture of said array over the operating distance range of said system.

4. A system in accordance with claim 3, wherein the successive focal ranges encompassing the points of refocusing, are of constant length and of substantially constant resolution.

5. A system in accordance with claim 3 in which said means adjusting the focal length effects different adjustments in accordance with the number of symmetrically disposed outer pairs which are activated.

6. A system in accordance with claim 1 in which said means for reducing the gain periodically fully disables said one or more symmetrically disposed outer pairs of elements to effect said reduction of the effective aperture of said array.

7. A phased array acoustic beam scanning system comprising:

a linear array of side by side transducer elements for transmitting an acoustic beam into a region of interest, and receiving acoustic energy reflected from points within said region;

first means for applying repetitive electric pulses to said elements to form said acoustic beam, and to receive from said elements electrical signals corresponding to said reflected acoustic energy, said means including delay circuit means for introducing time delays between said electrical pulses during transmission, and between said electrical signals during reception, said beam thereby being steered over a desired angular range in a plane transverse to said transducers;

second means synchronized with the application of said pulses to said elements for reducing the gain of at least a symmetric outer pair of elements of said array to reduce the extent of the active elements of said array during the time period in which near field reflected acoustic information arrive at said array; and

third means synchronized with said second means for further adjusting said time delays applied to said electrical signals during reception of said reflected energy to effect changes in the focusing of said reflected energy in accordance with the changes in the active elements of said array introduced by said second means, whereby improved performance may be maintained over an extended focal range.

8. A scanning system as in claim 7, which further includes display means receiving said electrical signals as delayed by said first and third means, and corresponding to said reflected acoustic information, for supplying a visual representation of said region.

9. A system as in claim 7 in which said second means fully disables said one or more symmetrically disposed outer pairs of elements to effect said reduction in active elements.

10. In a phased array ultrasonic imaging system including a linear array of side by side transducer elements for transmitting an acoustic beam into a region of interest, and receiving acoustic energy reflected from points within said region,

first means for applying repetitive electric pulses to said elements to form said acoustic beam, and to receive from said elements electrical signals corresponding to said reflected acoustic energy, said means including delay circuit means for introducing time delays between said electrical pulses during transmission, and between said electrical signals during reception, said beam thereby being steered over a desired angular range in a plane transverse to said transducers,

second means synchronized with the application of said pulses for repeatedly further adjusting said time delays applied to said electrical signals during reception of said reflected acoustic energy to effect changes in the focal length of said array, and

display means for supplying from said electrical signals from reflected energy a visual representation of said region, the improvement which comprises:

third means for reducing the gain of at least one outer element of said array during the arrival of near-field reflected acoustic information, and for restoring said gain thereafter to thereby effect changes in the effective aperture of said array, and for controlling said changes in focal length in accordance with said changes in said effective array aperture, whereby resolution of said visual representation is improved over an extended focal range.

11. An imaging system as in claim 10, in which said second means effects said changes in focusing in discrete steps, the occurence of said steps varying under the control of said third means at least in part with said changes in effective aperture of said array.

12. An imaging system as in claim 10, in which said third means reduces the gain of at least one symmetric outer pair of elements of said array.

13. An imaging system as in claim 10, in which said third means reduces the gain of a succession of outer symmetric pairs of elements, and controls said second means to superimpose time delays on said electrical signals in synchromism with said successive changes of outer element pair gain.

14. An imaging system as in claim 13 in which said reduction of gain of said successive outer symmetric element pairs provides successively smaller effective array apertures, each said aperture having an optimal near-field focal range associated therewith, each said aperture being successively utilized for information arriving from the respective near-field focal range associated therewith, said second means refocusing by readjusting with each such successive aperture change said time delays of said received electrical signals to accord with said focal range associated therewith.

15. An imaging system as in claim 14, in which said second means readjusts said time delays for said electrical signals to provide with each successive aperture change a focal length approximating the midpoint of the focal range associated with each said aperture.

16. An imaging system as in claim 14 or 15, in which said focal ranges associated with each of said apertures are approximately equal.