Surgery – Truss – Pad
Patent
1995-06-08
1997-08-12
Smith, Ruth S.
Surgery
Truss
Pad
128696, 128731, A61B 500
Patent
active
056555342
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and apparatus for separating the different components of evoked electric and magnetic responses, spontaneous activity of the brain, as well as signals measured from the heart, said components being generated by different sources, said separation of signal components from each other taking place by virtue of subtracting linear combinations of signals obtained from a number of or all measurement channels from the signals obtained from a number of or all measurement channels.
The function of the body can be studied by measuring the electric field E and the magnetic field B. Electric field is ordinarily measured by placing electrodes on the skin and then recording the differential potentials between these. Magnetic field is customarily measured with the help of superconducting SQUID magnetometers. The external measurement of electric brain waves is conventionally called electroencephalography, or EEG; analogously, the measurement of magnetic fields generated by the brain is called MEG, while the measurement of electric potentials resulting from the activity of the heart is called electrocardiography, or ECG, and the measurement of magnetic fields generated by the heart is respectively called magnetocardiography, or MCG [Cf., e.g., J. Nenonen and T. Katila, "Noninvasive Functional Localization by Biomagnetic Methods", J. Clin. Eng. 16, 423-434 and 495-503 (1991)]. In both electrical and magnetic measurements the measurement signal is a weighted sum of the active current flowing in the tissue, herein called the primary current J.sup.p (r,f). If the output signal of a given measurement channel (denoted by the subindex i) is denoted by the symbol X.sub.i, the output signal can be expressed: (1) is, the volume of the primary current origin and where the sensitivity function of the measurement channel i for the primary current density at point r is L.sub.i (r). This sensitivity function is ordinarily called the lead field of the measurement channel, because it expresses the weight at which the primary current distribution is coupled to the measurement signal in question. The term n.sub.i (t) in Eq. (1) represents the effect of noise on the output signal of channel i. The signals of the different channels define a time-varying signal vector vector can be visualized as a vector of a space whose dimensionality and number of base vectors is equal to the number of measurement channels. Such a space is called the signal space. Typically, the number of measurement channels in the EEG measurements which the present invention relates to is 16-128, in MEG measurement 19-122, and in MCG measurements roughly on the same order of magnitude, while with the evolving techniques, the numbers of channels tend to grow.
Frequently, the primary current distribution intriguing the researcher is composed of a multitude of separate components evolving from primary current densifications at different locations. The term "component" in this context refers to a source whose location and orientation are constant, while its amplitude is time-varying. Such a component has identical time-varying behavior in all measurement channels; however, it is represented in each channel multiplied with a different weight factor depending on the fashion the channel in question is coupled to said source component as expressed in Eq. (1), in other words, depending on the lead field of the channel or sensitivity function L.sub.i (r) at the location of the contributing source. Owing to the temporal coincidence of these components and their weighted summation in the different measurement channels, the measurement results frequently fail to provide sufficient information on the original location of each source, or even on the number and type of components contributing to the measured signals. The impediment arises from the complex summation of several different sources in the different measurement channels according to Eq. (1), thus making it difficult to resolve the contribution of an individual component in the total resp
REFERENCES:
patent: 5269325 (1993-12-01), Robinson et al.
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