Magnetic induction tomography systems of coil configuration

FIELD: electricity.

SUBSTANCE: invention is related to systems of magnetic impedance tomography. The system comprises an excitation system having several exciting coils to generate a magnetic excitation field intended to induce eddy currents in a surveyed volume, a measurement system with several measuring coils to measure the fields generated by the induced eddy currents, at that the measuring coils are placed in a volumetric (3D) geometrical assembly and a reconstruction device intended for the receipt of measurement data from the measurement system and for the reconstruction of the object imaging in the surveyed volume against the measured data. Each measuring coil covers an area and is oriented in essence transversely to the magnetic field power lines in the exciting coils, separate measuring coils cover jointly the area corresponding to the volumetric (3D) geometrical assembly, at that the exciting coils cover the area where the measuring coils are placed. The area covered by each of the separate measuring coils is oriented perpendicular to the area covered by the exciting coils.

EFFECT: usage of the invention allows improving the quality of imaging for volumetric objects.

8 cl, 2 dwg

 

The technical FIELD

The invention relates to a system of magnetic impedance tomography (MIT) with coil excitation system and coil measurement system. The excitation coil and the measuring coil is placed around the analyzed volume (VOI). In the General case, when the excitation coil is activated, in the conductive object in VOI-the amount of generated eddy currents. Using the measuring coils is measured magnetic field generated by these eddy currents. On the collected measurement data can be reconstructed conductivity characteristics of the object (such as images).

PRIOR art

Such a system of magnetic impedance tomography mentioned in the patent application U.S. 2008/0246472 as a system for the inductive measurement of bioimpedance conductive fabric.

In known magnetic impedance tomography is provided by generating coil for generating a primary magnetic field that passes through the conductive material (such as cloth). This flux induces in the tissue of the eddy currents. Only touch the coil measures the secondary magnetic field generated by the induced eddy currents. Generating coil and sensor coil is oriented perpendicularly. Thus, the resulting flow of genera the respective coils through the sensor coil, no. A known system of magnetic impedance tomography includes additional regulatory coil to "redeem" the primary magnetic field in the sensor coil. In the sensor coil detects only the secondary magnetic field.

A BRIEF STATEMENT of the substance of the INVENTION

The present invention is to create a magnetic impedance tomography, providing improved image quality, particularly for three-dimensional objects.

This task is solved by using the magnetic impedance tomography according to the invention, containing:

the excitation system with multiple excitation coils for generating a magnetic field excitation order to induce eddy currents in the test volume,

measuring system with multiple measuring coils to measure the fields generated by the induced eddy currents,

while measuring coils are three-dimensional (3D) geometric pattern, and

separate measuring coil is oriented essentially transverse to the magnetic field lines of the excitation of the exciting coils, and

the device for the renovation, designed for receiving measuring data from the measuring system and the reconstruction of the object image in the investigated volume change is sustained fashion data.

The measuring coil is located at the 3D-surround arrangement, so that the measuring coil surrounds or partially covers surround the study area. Thus, three-dimensional object, such as the patient's head, you want to examine, may be placed in the bulk region, and eddy currents induced in the object can be measured. Measurements for the respective measuring coils can be performed simultaneously, i.e. in parallel, so to obtain data on the volume of the object in VOI-volume requires only a short period of time of measurement equal to several seconds or less. In an alternative embodiment, may be carried out serial control coils, so that the activated volumes (e.g., pairs) of coils located in different, for example, opposite positions around the investigated volume. When a large number of measurements that contain independent information, the quality of the reconstructed image increases due to higher content of total measurement information, and therefore, due to noise reduction and maintenance of the artifacts.

In addition, the excitation coil arranged to surround the analyzed volume. Separate measuring coil is oriented essentially transverse to the magnetic field lines, Shine the new coil excitation. For example, if the excitation coil generates a uniform magnetic field in which the lines of force of the field are parallel measuring coils are arranged transversely to the exciting coils. Thus, the measuring coil is little or no grasp of the flow of the magnetic field of the excitation generated by the exciting coils. When a uniform magnetic field excitation is generated by the excitation coils in the volume under study. Therefore, the dynamic range of signals received by the measuring coils, substantially reduced compared with the signals generated by the magnetic field excitation, the sensitivity to induced magnetic field caused by the eddy currents increases. In addition, the small dynamic range allows use in the measuring system, ultra low noise amplifier with a constant gain.

Measuring data from the measuring coils are fed into the device for the reconstruction, which reconstructs the image, namely the three-dimensional image of the object in the volume under study.

These and other aspects of the invention will further be explained with reference to embodiments of defined in the dependent claims.

There are various ways of configuring the exciting coils izmeritelnaya coils, thus, the measuring coil are oriented transversely to the magnetic field excitation. A simple arrangement is to provide a pair of exciting coils are oriented in parallel. Standard Helmholtz allows to obtain good results for the excitation coils. For a pair of Helmholtz coils requires only one power source. The solenoid coil has a very high homogeneity of the magnetic field excitation and also requires only one power source. Additionally, many of coil pairs of Helmholtz can be controlled in parallel, in connection with a single power source, or for the respective pairs of coils may be provided with a separate power supply. In each of these configurations of the measuring coil can be oriented transversely to the exciting coils.

In one embodiment of the invention, the excitation coil are located in a configuration that is similar to the scheme Helmholtz, for excitation of a uniform magnetic field. A uniform field is distributed in the region between the coils of each coil pair of Helmholtz. A pair of Helmholtz coils has two identical circular magnetic coils located symmetrically one on each side of the investigated volume along a common axis, being separated by distance h, while for the classical Helmholtz coils, the value of h is equal to the radius R of the coil. In the process of working on each coil passes the same electric current flowing in one direction. Setting h=R, which defines a pair of Helmholtz coils, it is possible to minimize the inhomogeneity of the field (B) in the center of the coils.

In another example, the excitation coil is made in the form of a solenoid that generates a magnetic field that is uniform in the Central region of the solenoid. The Central region of a uniform magnetic field increases (along the longitudinal axis of the solenoid) with increasing length of the solenoid.

In one aspect of the invention, the system of magnetic impedance tomography has a measuring coil, located at the geometric arrangement of the hemisphere. Namely, the centers of the measuring coils are located on the surface of the hemisphere, while the area of the loop coil is oriented transverse to the magnetic field lines generated by the exciting coils. This layout of the measuring coil are close, i.e., at a small distance from the volumetric object. Object distance should be as small as possible to ensure high sensitivity, it is limited only by practical constraints, such as suitability for different volumes or production considerations. For objects like the human head, the allowable distance from 1 to 4 see Poem is this, the sensitivity of the measuring system has a more uniform spatial distribution compared to the MIT systems in which the excitation coil and the measuring coil are on the same level.

In an additional aspect of the invention, the excitation coil electrically connected to opposite ends of the investigated volume. Thus, the data of the excitation coil are activated simultaneously in order to create a homogeneous magnetic field in the investigational volume.

In an additional aspect of the invention, the excitation coil is located on the surface of metallic or non-metallic cylinder transversely to the longitudinal axis of the cylinder. Metal cylinder provides a very reliable protection against electromagnetic disturbances coming from the outside. Can also be used a simple non-metallic, such as plastic, cylindrical media. Thus, in the investigated volume is generated by a uniform magnetic field. The excitation coil may be activated simultaneously or sequentially in combination with the corresponding parts of the exciting coils. For example, the excitation coil can be activated in a sequential pairs of Helmholtz coils.

In another aspect of the invention, the measuring coil is slightly tilted. Thus, it can be compensated for the minor is entrusted to the inhomogeneity of the magnetic field excitation. System magnetic impedance tomography according to the invention, for example, has a magnetic field sensors, for example in the form of coils of the reference signal for measuring the local magnetic field. Based on the orientation of the measured local field of the measuring coil can be tilted so as to be precisely perpendicular to the local direction of the magnetic field excitation.

In an additional aspect of the invention, the measuring coils are located on a non-metallic medium such as a plastic holder. Separate measuring coil on a non-metallic carrier located transverse to separate the excitation coils located on the cylinder. These and other aspects of the invention will be discussed with reference to the embodiments of described below and with reference to the accompanying drawings.

BRIEF DESCRIPTION of DRAWINGS

The invention is further explained in the description of the preferred variants of the embodiment with reference to the accompanying drawings, in which:

Fig.1 schematically depicts a system of magnetic impedance tomography according to the invention.

Fig.2 schematically depicts the scheme for two Helmholtz coils.

DESCRIPTION of the PREFERRED EMBODIMENT VARIANTS of the INVENTION

In Fig.1 is a schematic representation of a system of magnetic impedance tomography according to image ateneu. The excitation system 10 includes a coil 11 of the excitation and the excitation circuit 13. The coil 11 of the excitation is located on the cylindrical surface of cylinder 12. The excitation circuit 13 is provided for the selective excitation of the exciting coils. The excitation circuit 13 includes current sources of excitation coils. For example, the circuit delivers electric current to the pair of coils 11 excitation, located under the scheme Helmholtz (see Fig.2). The excitation circuit 13 is controlled by computer system 30. The computer system 30 may be a generic computer with appropriate software. Alternative computer system 30 is a specialized processor.

The measuring system 20 includes a measuring coil 21 and the measuring circuit 22. The centers of the measuring coils 21 are located on the surface of the hemisphere. Thus, the measuring coils 21 are arranged around the investigated volume 3. Additionally, the area covered by their respective turns of the measuring coil 21, is oriented perpendicularly to the areas covered by the coils 11 of the excitation. Namely, the field coils of the measuring coils 22 are parallel to the surface of the cylinder 12, which pass through the coils of the coil excitation. Additionally, the measuring circuit 22 is connected to measure the elegance coils for receiving voltage signals, induced in the measuring coil by eddy currents in the object located in the monitored volume 3. The measuring circuit is controlled by computer system 30. For example, the measurement results receive sequentially or simultaneously from the respective sets of the measuring coils located in the same longitudinal position around the cylinder walls, when the excitation of pairs of Helmholtz coils located near this longitudinal position. Under alternative a few pairs of exciting coils Helmholtz can be activated by the excitation circuit 13 in parallel, and the measurements are performed in parallel on multiple measuring coils. The measuring circuit includes one or more ultra-low noise amplifiers. These amplifiers have a very low noise level which is less than lnV/√Hz at a constant gain of 20 dB or more and, thus, due to the restriction in the supply voltage have a limited input voltage range. The output signals of the measuring circuit are received in the device 4 reconstruction, which reconstructs image data from the output signals. The reconstructed image is displayed on the display 31. The reconstruction device may be incorporated, for example, software in the computer system 30.

The measuring circuit may also receive reference signals from the magnetic field sensors, such as coil reference signals close to the exciting coils to measure the excited magnetic field. One or more coils of the reference signals are arranged in parallel to the exciting coils. It is also possible to measure the current flowing in the coil excitation, in order to obtain the reference data. The measuring circuit delivers these reference signals in an electronic system, in which the reference data is used in conjunction with measured data for the calculation of the data phase for the measured data.

The measuring coil may also be formed in the magnetic field excitation to compensate for the inhomogeneities of the field. This is achieved by tilting the measuring coils so that the measured part of the magnetic field excitation was as low as possible (if there is no conductive object in VOI-volume, eddy currents are not generated).

In Fig.2 is a schematic representation scheme for two Helmholtz coils. Scheme Helmholtz creates a uniform magnetic field excitation in the region between the coils of the individual coil pairs schemes Helmholtz. A pair of Helmholtz coils has two identical circular magnetic coils located symmetrically one on each side of the investigated volume of the Dol common axis and separated by distance h, equal to the radius R of the coil. In the process of working on each coil passes the same electric current flowing in one direction. Setting h=R, which defines a pair of Helmholtz coils, it is possible to minimize the inhomogeneity of the field (B) in the center of the coils by the condition d2B/dx2=0 (where x is taken along the direction of separation of the two coils), and the field strength can vary by about 6% between the center and the planes of the coils. A slight increase in h leads to a decrease of the difference in field strength between the center and the planes of the coils by reducing the field uniformity in the area close to the center, as measured by the value of d2B/dx2. The more exciting coils operate in parallel under the scheme Helmholtz (i.e., parallel electric currents flow in opposite coils spaced at a distance equal to the radius of the coils), the higher the homogeneity of the field excitation.

1. System magnetic impedance tomography, containing
the excitation system with multiple excitation coils for generating a magnetic field excitation order to induce eddy currents in the test volume,
measuring system with multiple measuring coils to measure the fields generated by the induced eddy currents,
while measuring coils are about jemni (3D) geometric layout, and
each of the separate measuring coils, covers the area and is oriented essentially transverse to the magnetic field lines of the excitation of the exciting coils, a separate measuring coils together cover an area corresponding to three-dimensional (3D) geometric layout, and coil excitation cover the area in which are located the measuring coil, and the area covered by each of the separate measuring coils are oriented perpendicular to the area covered by the exciting coils, and
the reconstruction device designed for receiving measuring data from the measuring system and the reconstruction of the image of the object in the test volume from the measured data.

2. The system under item 1, in which the excitation system includes a pair of exciting coils are configured in parallel, in particular, located under the scheme Helmholtz, or arranged in the form of a solenoid.

3. The system under item 1, in which the measuring coil have centers located on the surface of the hemisphere.

4. The system under item 1, in which the two coil excitation at opposite ends of the investigated volume electrically connected.

5. The system under item 1, in which the excitation coil is located on the surface of the cylinder, while the measuring coils are arranged transversely ol the longitudinal axis of the cylinder.

6. The system under item 1, in which the excitation system is made with the possibility of excitation of the exciting coils in pairs.

7. The system under item 1, in which a separate measuring coil is oriented with a slight incline relative to the axis in the diagram Helmholtz, so as to intersect the local magnetic field generated by the exciting coils.

8. The system under item 1, in which the measuring coils are located on a non-metallic media.



 

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