Patent No. 5170119 Process and apparatus for determining the biocurrent distribution of a living body when the exact number of field sources is not known

 

Patent No. 5170119

Process and apparatus for determining the biocurrent distribution of a living body when the exact number of field sources is not known (Sekihara, et al., Dec 8, 1992)

Abstract

A process and an apparatus for measuring the biocurrent distribution call for initially assuming a number of multiple currents which is more than the number of isolated currents possibly existing in a living body and calculating the virtual magnetic field created by the assumed currents at actual measuring points. The estimated location and current vectors of said assumed currents are consecutively changed to decrease the difference between said virtual and actual magnetic fields so that the estimated location and current vectors of the assumed currents having the number corresponding to the true isolated currents substantially approximate the true values and the estimates of the other assumed currents approximate zero. This enables the biocurrent distribution to be exactly determined even when the number of isolated currents is not preliminarily known.

Notes:

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process and an apparatus for measuring the biocurrent distribution of a living body to obtain a solution exactly showing the biocurrent distribution even if the number of the magnetic field sources, that is, the exact number of the current dipoles in a living body to be measured is not known.

In order to accomplish the above-mentioned object, in accordance with the present invention, multiple currents larger in number than the numbers of the isolated currents which are expected to exist in a living body are assumed, and a virtual magnetic field created by each assumed current at an actually measured point is calculated. The estimated location and current vectors of the assumed currents are changed to reduce the difference between the virtual magnetic field and the actual magnetic field for determining the optimum estimates. In this case, the absolute values of the excess assumed current vectors are approximated to zero.

If multiple isolated currents, for example, current dipoles larger in number than the number of currents actually existing are assumed and the estimates ar changed so that the matching between the distribution of the magnetic field calculated from the assumed current dipoles and the distribution of the actually measured magnetic field is enhanced, an excessive degree of freedom would be introduced. Accordingly, there is the high possibility that a solution,, different from the actual current distribution will be obtained. In other words, it is presumed that the magnetic field formed at the measuring point may be substantially equal to the magnetic field formed by the current dipole assumed as a true current dipole (refer to equation (1)), if the current vector of the current dipole which is assumed to be located at a position closer to the measuring point than the position of the true current dipole is smaller than the true current dipole.

Hence, in accordance with the present invention, a fact is considered that the assumed current dipoles are more than the true current dipoles in magnitude by the number of the assumed current dipoles over the number of true current vectors of the assumed current dipoles if the assumed current dipoles are compared with the true current dipoles in only the magnitude or the energy (for example, magnetic field) which they give.

That is, when optimum values of the estimated locations and current vectors of the currents are determined so that the difference between the magnetic field calculated from the assumed currents and the actual magnetic field becomes smaller, the excessive degree of freedom of the optimum values is restricted by decreasing the magnitude of the current dipoles or the energy that they give so that the optimum values of the current vectors of the assumed currents which are an excess over the number of the true currents approximate to zero.

In accordance with the present invention, an excessive freedom degree of freedom is restricted by using the total sum or the total sum of the .alpha.-th power of the absolute values of the current vectors of the assumed current dipoles, or the total sum of the magnitudes of the magnetic fields, each formed solely by each assumed current dipole or the total sum of the .alpha.-th power of the magnitudes thereof.