Patent No. 6374131 Biomagnetism measuring method and apparatus

 

Patent No. 6374131

Biomagnetism measuring method and apparatus (Tomita, et al., Apr 16, 2002)

Abstract

A technique for accurately determining states of bioelectric currents occurring in particular positions in a site of interest of a patient. Transfer functions between the particular positions and each magnetic sensor are derived from a positional relationship between the site of interest and each magnetic sensor. Weight coefficients are computed from an inverse matrix obtained by adding a predetermined value to a matrix of the transfer functions, and virtual biomagnetism information obtained virtually by bioelectric currents set to the particular positions. Enhanced biomagnetism information with only the biomagnetism from the particular positions enhanced is acquired by superposing the weight coefficients of measured biomagnetism information. Based on this enhanced biomagnetism information, states of bioelectric currents occurring in the particular positions are determined accurately.

Notes:

SUMMARY OF THE INVENTION

This invention has been made having regard to the state of the art noted above, and its object is to provide a biomagnetism measuring method and apparatus for accurately determining bioelectric currents occurring in particular positions in a patient's site of interest, without being affected by noise included in measured biomagnetism information.

This above object is fulfilled, according to this invention, by a biomagnetism measuring method for measuring, with a plurality of magnetic sensors arranged adjacent a site of interest of a patient, biomagnetism generated from bioelectric currents flowing in the site of interest, and determining the bioelectric currents based on measured biomagnetism information acquired through the measurement, the method comprising the steps of:

computing transfer constants indicating degrees by which the biomagnetism is transferred from each particular position in the site of interest to each of the magnetic sensors;

regulating a matrix of the transfer constants;

computing a weight coefficient for each of the magnetic sensors to enhance biomagnetism generated from the particular position, based on virtual biomagnetism information virtually measured by the magnetic sensors and an inverse matrix of the regulated matrix, when a known bioelectric current is set to the particular position;

collecting measured biomagnetism information acquired by measuring the biomagnetism generated from the site of interest with the magnetic sensors;

computing enhanced biomagnetism information having the biomagnetism generated from the particular position enhanced by applying the weight coefficient to the measured biomagnetism information measured by each of the magnetic sensors; and

determining a bioelectric current in the particular position based on the enhanced biomagnetism information.

According to this invention set out above, a transfer function indicating a degree of transfer of biomagnetism in space is determined based on Biot-Savart's law, for example. Transfer constants are obtained by substituting, for the transfer function, particular positions in the site of interest of the patient and positional relationships thereof with the respective magnetic sensors. A matrix formed of the transfer constants is regulated, whereby a solution of the matrix has a value remote from zero. This lessens the unstable condition of the matrix occurring when the solution of the matrix is very close to zero. Further, a weight coefficient is computed for each of the magnetic sensors to enhance biomagnetism generated from each particular position, based on virtual biomagnetism information virtually measured by the magnetic sensors and an inverse matrix of the regulated matrix, when a known bioelectric current is set to the particular position. These weight coefficients, which are based on an inverse matrix in a stabilized condition, enhance only the biomagnetism from the particular positions. Then, enhanced biomagnetism information is computed by applying the weight coefficients to the measured biomagnetism information obtained by measuring, with the magnetic sensors, the biomagnetism generated from the site of interest of the patient. The bioelectric currents in the particular positions are determined based on the enhanced biomagnetism information. Thus, this invention can avoid the inconvenience encountered in the prior art in which weight coefficients based on the inverse of a matrix whose solution is close to zero are applied to the measured biomagnetism information, thereby enhancing even noise included in the measured biomagnetism information. As a result, the invention enables a correct determination of the states of bioelectric currents, e.g. current sizes, directions and locations, in particular positions in a patient's site of interest.

Preferably, the method according to this invention further comprises the step of outputting an arrow map showing the bioelectric current in each particular position in form of an arrow, the step of outputting an arrow map showing the bioelectric current in each particular position in form of an arrow, as superposed on a tomographic image including the particular position, the step of outputting an intensity distribution chart of the bioelectric currents generated in the site of interest, or the step of outputting a waveform chart of biomagnetism measured by each of the magnetic sensors. This method will then facilitate a visual recognition of the states of bioelectric currents in the particular positions in the patient's site of interest or the states of biomagnetism measured. This feature is of advantage to diagnostic situations and the like.

It is preferred that the matrix regulating step is executed to add a predetermined value for a solution of the matrix of the transfer constants to be remote from zero. The predetermined value, preferably, is at least one of a unit matrix or a penalty matrix having a predetermined size. It is also preferred that the predetermined value is at least one of a unit matrix or a penalty matrix having a size corresponding to noise included in the measured biomagnetism information.

In another aspect of this invention, a biomagnetism measuring apparatus is provided for measuring, with a plurality of magnetic sensors arranged adjacent a site of interest of a patient, biomagnetism generated from bioelectric currents flowing in the site of interest, and determining the bioelectric currents based on measured biomagnetism information acquired through the measurement, the apparatus comprising:

a plurality of magnetic sensors arranged adjacent the site of interest;

a transfer constant computing device for computing transfer constants indicating degrees by which the biomagnetism is transferred from each particular position in the site of interest to each of the magnetic sensors;

a regulating device for regulating a matrix of the transfer constants;

a weight coefficient computing device for computing a weight coefficient for each of the magnetic sensors to enhance biomagnetism generated from the particular position, based on virtual biomagnetism information virtually measured by the magnetic sensors and an inverse matrix of the regulated matrix, when a known bioelectric current is set to the particular position;

a measured information collecting device for collecting measured biomagnetism information acquired by measuring the biomagnetism generated from the site of interest with the magnetic sensors;

an enhanced biomagnetism information computing device for computing enhanced biomagnetism information having the biomagnetism generated from the particular position enhanced by applying the weight coefficient to the measured biomagnetism information measured by each of the magnetic sensors; and

a bioelectric current computing device for determining a bioelectric current in the particular position based on the enhanced biomagnetism information.

With this apparatus, the weight coefficient computing device computes a weight coefficient for each of the magnetic sensors to enhance biomagnetism generated from the particular positions in the site of interest, based on an inverse matrix of the matrix regulated by the regulating device, and on virtual biomagnetism information. The bioelectric current computing device determines bioelectric currents in the particular positions based on the enhanced biomagnetism information obtained by applying the weight coefficients to the measured biomagnetism information.

Preferably, the apparatus according to this invention further comprises an output device for outputting an arrow map showing the bioelectric current in each particular position in form of an arrow, an arrow map showing the bioelectric current in each particular position in form of an arrow, as superposed on a tomographic image including the particular position, an intensity distribution chart of the bioelectric currents generated in the site of interest, or a waveform chart of biomagnetism measured by each of the magnetic sensors.

Preferably, each of the magnetic sensors employed in the apparatus according to this invention is a high-sensitivity magnetic sensor including, for example, a coil, and a super-conducting quantum interference device connected to the coil.

The regulating device of the above apparatus may, for example, add a predetermined value for a solution of the matrix of the transfer constants to be remote from zero. Preferably, the predetermined value is at least one of a unit matrix or a penalty matrix having a predetermined size. It is also preferred that the predetermined value is at least one of a unit matrix or a penalty matrix having a size corresponding to noise included in the measured biomagnetism information.

The apparatus according to this invention may further comprise a stimulating device for applying at least one of an electric stimulation, an acoustic stimulation and an optical stimulation.

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The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.