Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Utility Patent
1998-10-02
2001-01-02
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S463000, C600S467000
Utility Patent
active
06168564
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to intracardial ultrasonic imaging, particularly to a one-dimensional linear transducer array useful for detecting ultrasonic signals in real time in an intracardial environment, i.e., within the heart chambers, wherein a transducer array is employed.
Transducer arrays are employed to provide transmit ultrasonic signals and to collect data for reconstruction of an image from the ultrasonic artifacts reflecting off of features.
Scanning transducer arrays are known such as those described an article by Gattzke et al., “Electronic Scanner of a Phased-Array Ultrasound Transducer,” Hewlett-Packard Journal, December 1983, pp. 13-20., and in a text by Prof. Albert Macovski, Medical Imaging Systems, Chapter 10, “Utrasonic Imaging Using Arrays,” Prentice-Hall, 1983. A phased array acoustic imaging system with an active aperture has been described in U.S. Pat. No. 4,550,607 issued to Maslak et al. Nov. 5, 1985.
Two parameters are important in phased array transducers: beam steering and beam focussing. The current state of the art requires that transducer elements be spaced at about one-half wavelength of the center frequency of excitation along an axis in order for the resultant beam to be steerable off normal from the axis. It is known that undesired grating lobes manifest in directions other than the steered direction, especially where the steered direction is away from the normal axis and where the spacing exceeds one-half wavelength.
As is known in the art, such as Chapter 10 of the Macovski text, the field pattern of a linear array in the near field has a linear phase factor and a quadratic phase factor. Structures have been suggested to eliminate the quadratic term to simplify processing. Heretofore, structures have not been satisfactory, because of difficulties in maintaining control of the beam formation, steering and scanning.
In some applications, it is not necessary to steer a beam. For example, a linear array on a straight, flat axis does not require steering if the regions of investigation are normal to the array. Thus, an image may be generated by translating an active aperture between the array and the target along the axis of the array so that all radiated and received ultrasonic signals are normal to the array. In these cases, the spacing of the elements can typically be as large as one wavelength or more and still not have unacceptable grating lobes. On the other hand, the disadvantage of such a linear array is that a rectangular image size is governed by the transducer aperture which is built from the image lines, where the active aperture defines a beam width. To allow for larger image size while retaining a small transducer aperture, the transducer array is typically curved such that a convex surface directs the ultrasound beam in a divergent fashion to over a larger field of view. Requiring that the array be curved limits the flexibility of a transducer array. There are circumstances where bending of a transducer array, particularly in an enclosed chamber such as the heart cavity, is undesirable. What is needed is a mechanism whereby a transducer array can be used both to steer and to focus with minimal interaction between steering control and focus control so that real-time imaging can be achieved.
SUMMARY OF THE INVENTION
According to the invention, in an ultrasonic imaging system, a transducer array structure, preferably a linear one-dimensional array on a catheter, is provided wherein the beam steering is controlled by a preselected delay profile implementing a linear portion of a beam forming equation so that the array is effectively curved electronically, thus avoiding the need to curve the transducer array physically, as may be undesirable in such an application as intra-cardial imaging. An active aperture is provided for beam-steering, the aperture comprising selected adjacent subsets of transducer elements of the array structure. The preselected delay profile may be implemented by delay lines to each transducer element or by any preselected delay pattern selected to match the desired flatness or curvature of the array structure. The beam translation and steering can be implemented by simple activation of that portion of the array forming the active aperture, with the delay profile across the entire transducer array invoking the steering of the beam. The pitch or separation between the transducer elements may be uniform or varied. Varied pitch permits sparser spacing of transducer elements along portions of the array structure. A quadratic portion of the beam forming equation is implemented in a beam former to control focus of the elements of the active aperture at each position of the active aperture.
One of the advantages of this invention is that a phased array beam former can be implemented like a simple linear array beam former. A delay profile implements the linear portion of the beam forming equation for steering, while focussing is effected substantially independently by control of the quadratic portion of the beam forming equation. Because of relaxed requirements on the phased array, fewer elements are needed in the array, particularly in the center, since beams need only be steered using the linear portion of the beam-forming equation at the edges of the array.
The invention will be better understood by reference to the following detailed description in conjunction with the accompanying drawings.
REFERENCES:
patent: 4180790 (1979-12-01), Thomas
patent: 4334432 (1982-06-01), Gill
patent: 4542653 (1985-09-01), Liu
patent: 4550607 (1985-11-01), Maslak et al.
patent: 4699099 (1987-10-01), Maslak et al.
patent: 5651366 (1997-07-01), Liang et al.
patent: 5680863 (1997-10-01), Hossach et al.
patent: 5784336 (1998-07-01), Gopinathan et al.
patent: WO 97/01768 (1997-01-01), None
Gattzke et al., “Electronic Scanner of a Phased-Array Ultrasound Transducer,” Hewlett-Packard Journal, Dec. 1983, pp. 13-20.
Prof. Albert Macovski, Medical Imaging Systems, Chapter 10, “Ultrasonic Imaging Using Arrays,” Prentice-Hall, 1983.
Jaworski Francis J.
Sci-Med Life Systems, Inc.
Townsend and Townsend / and Crew LLP
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