Surgery – Truss – Pad
Patent
1994-01-25
1995-11-14
Hindenburg, Max
Surgery
Truss
Pad
36441315, A61B 505
Patent
active
054657300
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to electrical impedance tomography (EIT). EIT is a relatively recently developed imaging technique which can be used for medical purposes and is capable of producing tomographic images of changes in the spatial distribution of conductivity within a body segment. This is clinically useful, since these variations are brought about by physiological changes occurring in the body, such as lung ventilation, blood flow and gastric emptying.
DESCRIPTION OF RELATED ART
In such medical use of the technique, an alternating current, typically of some 5 mA at a frequency of about 50 kHz, is injected via two or more of, say sixteen standard electrodes spaced around the body segment. The potential at the remaining electrodes is sampled and passed to a computer for further analysis. The technique offers several advantages such as a fast data collection rate and a relatively low cost of the equipment. It is also safe and non-invasive and can be used for continuous monitoring.
Developments in this field can be categorized broadly into instrumentation (hardware) and image reconstruction (software). The former addresses the problems associated with data collection and the latter is concerned with producing images from the data.
Although, strictly speaking, the problem of image reconstruction is non-linear, it is now well established that even linear methods of reconstruction are capable of producing clinically useful, although perhaps non-optimal, images.
The problem of reconstructing, from the measured date, an image representing the nonuniform distribution of conductivity over a body segment is, in effect, the inverse of the simpler problem of calculating what the measured data would be if the conductivity distribution were known, and various algorithms for treating the data to solve the inverse problems have already been proposed: for example a method based on the concept of back-projection, due to Barber and his collaborators at the University of Sheffield, England, is disclosed and discussed in U.S. Pat. No. 4617939 and in their paper (Imaging spatial distributions of resistivity using applied potential tomography: Barber D. C., Brown B. H. and Freeston I. L. in Electronic Letters (1983) 19 (22), 933-5), and an iterative method due to Kotre is described in another paper (A sensitivity coefficient method for the reconstruction of electrical impedance tomograms: Kotre C. J., in Clin. Phys. Physio. Meas. (1989) 10, 275-81).
In the wider mathematical context, a known method of approaching inverse problems of this general kind is the method of spectral expansion, and this method has indeed been applied to the solution of practical problems in the field of geophysics as described in a paper by Inman J. R., Ryu J. and Ward S. H. entitled "Resistivity Inversion" published in Geophysics (1973) 38 (6), 1088-108. Spectral expansion has also been used as a means of analyzing at least one of the known methods (Kotre's) of reconstructing an electrical impedance tomographic image, but it has not hitherto been proposed to employ spectral expansion directly in the process of reconstructing a tomographic image of an object by the method of electrical impedance tomography. However, it is now perceived that the technique of spectral expansion may be so employed with considerable advantage.
SUMMARY OF THE INVENTION
It is an object of the resent invention to provide an improvement in the reconstruction of images produced by the use of EIT, and this object is achieved according to the invention by the application of spectral expansion techniques in the reconstruction of EIT images.
According to the invention, therefore, a method of producing an electrical impedance tomographic image of an object is provided, comprising the steps of: positioning a plurality of electrodes peripherally of the object in electrical contact therewith, repeatedly applying an electrical signal between at least two selected ones of the electrodes and measuring the resulting electrical potentials at others of the elec
REFERENCES:
patent: 4617939 (1986-10-01), Brown et al.
patent: 5272624 (1993-12-01), Gisser et al.
Geophysics, vol. 38, No. 6, 1973, pp. 1088-1108, J. R. Inman et al. "Resistivity Inversion" cited in the application--see p. 2.
Medical Physics, vol. 16, No. 2, 1989, New-York (US), pp. 162-169, D. C. Barber "a review of image reconstruction techniques for electrical impedance tomography"* see section VI : "Reconstruction Algorithms"*.
G. H. Golub et al., "Handbook Series Linear Algebra", Singular Value Decomposition and Least Squares Solutions, Numer. Math 14, 1970, pp. 403-420.
C. C. Barber et al., "Imaging Spatial Distributions of Resistivity Using Applied Potential Tomography", Electronics Letters, 27 Oct. 1983, vol. 19 No. 2, pp. 933-935.
M. Zadehkoochak et al., "A Transputer Implemented Algorithm for Electrical Impedance Tomography", Institute of Physical Sciences in Medicine, 1990 vol. 11 No. 3, pp. 223-230.
C. J. Korre, "A Sensitivity Coefficient Method for the Reconstruction of Electrical Impedance Tomograms", Clin. Phys. Physiol. Med., 1989, vol. 10 No. 3, pp. 275-281.
T. J. Yorkey, "Comparing Reconstruction Methods for EIT", Ph.D. Thesis, University of Wisconsin (Madison) 1986, pp. 104-123.
Blott Barry H.
Daniell Geoffrey J.
Zadehkoochak Mohsen
British Technology Group Ltd.
Hindenburg Max
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