Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2002-10-21
2004-04-13
Imam, Ali M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S447000, C128S916000
Reexamination Certificate
active
06719696
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of ultrasound imaging systems. In particular, the present invention relates to field deployable 3D ultrasound imaging systems providing high resolution images in real time.
BACKGROUND OF THE INVENTION
Ultrasound sensing and imaging technology provides a powerful tool for non-invasive imaging for treatment assessment and for minimally invasive surgery. Unlike CT scanners and MRI ultrasound imaging systems are compact and much cheaper to manufacture. These advantages allow use of ultrasound imaging systems in mobile units such as an ambulance or a helicopter. In general, victims of accidents, disasters or wars need immediate assessment and treatment in order to save their lives. For example, deployment of compact ultrasound imaging systems in mobile units allows on site imaging for treatment assessment during transportation providing live saving information for later surgery in a hospital or even providing information for minimally invasive surgery within the mobile unit. Therefore, it would be highly advantageous to provide a compact field-deployable 3D ultrasound imaging system for mobile units and field hospitals for immediate imaging of victims on accident sites, in disaster areas or in war zones.
However, state of the art ultrasound imaging systems suffer from very poor image resolution due to the very small size of sensor arrays of compact systems. Therefore, such systems do not provide images having a satisfying resolution for treatment assessment or surgery. In order to improve image quality it is necessary to deploy a large number of sensors in a compact multidimensional array to provide significant improvements in array gain for signals embedded in partially correlated noise fields. Partially correlated noise fields are caused, for example, by non-linear propagation characteristics of the human body and result in aberration effects and fuzziness in reconstructed images. The improvements in array gain result in image resolution improvements and minimization of the aberration effects.
An overview of the state of the art in adaptive and synthetic aperture beamformers is given in “Implementation of Adaptive and Synthetic Aperture Processing Schemes in Integrated Active-Passive Sonar Systems”, Proceedings of the IEEE, 86(2), pp. 358-397, February, 1998 by S. Stergiopoulos. These algorithms have been designed to increase the signal-to-noise ratio for improved target detection and to provide simultaneously parameter estimates such as frequency, time delay, Doppler shift and bearing for incorporation into algorithms localising, classifying and tracking acoustic signals.
To optimize the beam forming process, beamforming filter coefficients have to be chosen based on data received from a sensor array of the sonar system. In particular, the coefficients have to be chosen based on the statistical properties of the received data. Algorithms using characteristics of noise received from the sensor array for optimizing the beamforming process are called adaptive beamformers. The adaptive beamformers require knowledge of a correlated noise's covariance matrix. However, if the knowledge of the noise's characteristic is inaccurate, performance of the adaptive beamformer will degrade significantly and may even result in cancellation of a desired signal. Therefore, it is very difficult to implement useful adaptive beamformers in real time operational systems. Numerous articles on adaptive beamformers and the difficulties concerning their implementation have been published. Various adaptive beamformers such as the Generalized Sidelobe Cancellers (GSC), the Linearly Constrained Minimum Variance Beamformers (LCMV) and the Minimum Variance Distortionless Response (MVDR) are discussed in the following references, which are hereby incorporated by reference:
B. Windrow et al.: “Adaptive Antenna Systems”, Proceedings IEEE, 55(12), pp. 2143-2159, 1967;
N. L. Owsley: “Sonar Array Processing”, S. Haykin, Editor, Prentice-Hall Signal Processing Series, A. V. Oppenheim Series Editor, pp. 123, 1985;
B. Van Veen and K. Buckley: “Beamforming: a Versatile Approach to Spatial Filtering”, IEEE ASSP Mag., pp. 4-24, 1988;
J. Capon: “High Resolution Frequency Wavenumber Spectral Analysis”, Proc. IEEE, 57, pp. 1408-1418, 1969;
S. Haykin: “Adaptive Filter Theory”, Prentice-Hall, Englewood Cliffs, N.J., 1986;
T. L. Marzetta: “A New Interpretation for Capon's Maximum Likelihood Method of Frequency-Wavenumber Spectra Estimation”, IEEE-Trans. Acoustic Speech Signal Proc., ASSP-31(2), pp. 445-449, 1983;
A. H. Sayed and T. Kailath: “A State-Space Approach to Adaptive RLS Filtering”, IEEE SP Mag., pp. 18-60, July, 1994;
A. B. Baggeroer, W. A. Kuperman and P. N. Mikhalevsky: “An Overview of Matched Field Methods in Ocean Acoustics”, IEEE J. Oceanic Eng., 18(4), pp. 401-424, 1993;
H. Wang and M. Kaveh: “Coherent Signal-Subspace Processing for the Detection and Estimation of angles of Arrival of Multiple Wideband Sources”, IEEE Trans. Acoust. Speech, Signal Proc., ASSP-33, pp. 823-831, 1985;
J. Krolik and D. N. Swingler: “Bearing Estimation of Multiple Brodband Sources using Steered Covariance Matrices”, IEEE Trans. Acoust. Speech, Signal Proc., ASSP-37, pp. 1481-1494, 1989;
S. D. Peters: “Near-Instantaneous Convergence for Memoryless Narrowband GSC/NLMS Adaptive Beamformers”, submitted to IEEE Trans. Acoust. Speech, Signal Proc., January 1995;
L. J. Griffiths and C. W. Jim: “An Alternative Approach to Linearly Constrained Adaptive Beamforming”, IEEE Trans. on Antennas and Propagation, AP-30, pp. 27-34, 1982; and,
D. T. M. Slock: “On the Convergence Behavior of the LMS and the Normalized LMS Algorithms”, IEEE Trans. Acoust. Speech, Signal Proc., ASSP-31, pp. 2811-2825, 1993.
Unfortunately, implementation of adaptive beamformers in modern ultrasound systems comprising multi-dimensional arrays with hundreds of sensors requires very large amounts of memory and very large processing capabilities for real time data processing making their application for field-deployable systems impossible. To implement adaptive beamformers using current computer technology, the concept of partially adaptive beamformer design has been developed. The partially adaptive beamformer reduces the number of degrees of freedom, associated with the beamforming process, lowering the computational requirements and improving response time. Unfortunately, due to the reduction of the number of degrees of freedom the partially adaptive beamformers cannot converge to an optimum solution as fully adaptive beamformers. Therefore, the partially adaptive beamformers cannot make substantial use of multidimensional arrays deployed in ultrasound systems in order to improve array gain and to provide images with high resolution.
It is, therefore, an object of the invention to overcome the problems associated with the implementation of adaptive beamformers in modem ultrasound imaging systems comprising multidimensional sensor arrays.
It is further an object of the invention to provide adaptive beamformers with near-instantaneous convergence for ultrasound imaging systems deploying line arrays, circular arrays, spherical arrays of sensors or any superposition of these types of arrays.
It is yet another object of the invention to provide a 3D ultrasound imaging system comprising a multidimensional sensor array for generating high resolution images in real time using an adaptive beamforming process that is field-deployable.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided, an adaptive multidimensional beamformer having near-instantaneous convergence for ultrasound imaging systems. Implementation of the multidimensional beamformer according to the present invention provides the basis for a 3D ultrasound imaging system according to the present invention comprising a compact multidimensional sensor array and a compact processing unit that is field deployable and generates high resolution images in real time or near real time.
In accordance with the present invention t
Dhanantwari Amar C.
Stergiopoulos Stergios
Freedman & Associates
Her Majesty the Queen in right of Canada as represented by the M
Imam Ali M.
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