Electromagnetic Tomography in IRE RAS

Electrical Impedance Tomography (EIT)

EIT is the technique enabling to visualize spatial distribution of electrical impedance (or conductivity) inside the object, such as human body. The device uses voltage measurements on the object's surface when the electric current passes through the volume, as initial data for the image reconstruction. A suitable operation of the device requires both fast and effective reconstruction algorithms and high accuracy of electrical measurements. As the measurements in electrical impedance tomography can be made rather fast, high processing speed of the facilities enables to visualize many processes (such as heart pulsation) in real time. We are developing both the measurement equipment for EIT and methods of inverse problem solving.

The experimental electrical impedance tomograph and software are created, which are used now in medical researches, mainly in pulmonology. Main advantages of the developed approach are: the possibility of absolute conductivity visualization in a human body cross-section, high measurement rate up to 12 frames per second. As essential parts of the tomography system, there are the data processing system and database. According to the first clinical results, the new device is capable to diagnose number of pulmonary diseases including cancer, and therefore impedance tomography could substitute x-ray investigations in many cases as harmless and accessible method. The system is tested also currently as mean for lungs monitoring at premature babies. See the photos of EIT measuring equipment and reconstructed images of the human chest.

Visualization of absolute conductivity distribution inside the body (i.e. real anatomy) is still intriguing problem in EIT. During a few years our research group develops fast and robust static EIT imaging method, which is used currently with the experimental EIT systems. We develop this server to enable researchers from EIT community to try our algorithms with the data collected by different instruments and to estimate advantages of static in vivo EIT imaging. Examples of static images reconstructed with this server are presented in the EIT gallery.

The system enables to obtain images of the 3-D conductivity distribution in regions below the skin surface up to several centimeters deep. The 256-electrode measuring system and image reconstruction algorithm are used for breast tissues imaging and diagnostics, in particular, for malignant tumors detection. See the photo of the multifrequency electrical impedance mammograph MEM and examples of tomographic images obtained during clinical tests.

Magnetic Induction Tomography (MIT)

MIT unlike EIT doesn't requires electrical contacts with the body and uses interaction of oscillating magnetic field with conductive media. The field, which can be excited and registered by small coils arranged around the object, is perturbed by eddy currents in the object. The conductivity (and permittivity) can be reconstructed from the measurements of perturbed field outside the objects. We have developed theoretical base of induction tomography, reconstruction algorithm and forward problem solver for the simulation of measurements. Although the approximated equation for vector potential in case of MIT is very similar to the equation for scalar potential in case of EIT, there are important differences in solving corresponding inverse problems. The first experimental measuring system for MIT with 16 transmitting and receiving coils has been built and tested recently in the laboratory. First images are reconstructed successfully from the data measured on phantom with this system. Of course, the MIT approach can be used in many applications besides medicine due to contact-free operation and possibility to choose optimal frequency of magnetic field for given conductivity and size of the object under investigation.
See the illustrations of MIT basics, photo of the first measuring system and images reconstructed from the experimental data. The result of image reconstruction from the simulated data is also demonstrated.

Electric Field Tomography (EFT)

The EFT method exploits interaction of high-frequency electric field with inhomogeneous conductive medium without contact with the electrodes. Unlike an electrical impedance tomography no electric current is injected into the medium from the outside. The interaction is accompanied with high frequency redistribution of free charges inside the medium and leads to small and regular phase shifts of the field in the area surrounding an object. Such kind of phenomena is referred as the Maxwell-Wagner relaxation. Measuring the perturbations of the field using the set of electrodes placed around the object enables to reconstruct internal structure of the medium. Electric field of course can be used for imaging of dielectric (nonconducting) objects, this technique is known as electrical capacitance tomography (ECT). See the results of EFT imaging simulation.


Alexander Korjenevsky
E-mail:  korjenevsky@cplire.ru

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