Open AccessA THREE-PHASE INDUCTIVE SENSOR FOR IN VIVO MEASUREMENT OF ELECTRICAL ANISOTROPY OF BIOLOGICAL TISSUES
Author(s) -
Yukio Kosugi,
Toshiki Takemae,
Hiroki Takeshima,
Atsushi Kudo,
Kazuyuki Kojima,
Naofumi Tanaka
Publication year - 2014
Publication title -
contemporary materials
Language(s) - English
Resource type - Journals
eISSN - 1986-8677
pISSN - 1986-8669
DOI - 10.7251/comen1401001k
Subject(s) - anisotropy , materials science , electrical resistivity and conductivity , signal (programming language) , nuclear magnetic resonance , phase (matter) , magnetic field , current (fluid) , amplifier , biomedical engineering , acoustics , physics , optoelectronics , optics , computer science , medicine , cmos , quantum mechanics , thermodynamics , programming language
Biological tissue will have anisotropy in electrical conductivity, due to the orientation of muscular fibers or neural axons as well as the distribution of large size blood vessels. Thus, the in vivo measurement of electrical conductivity anisotropy can be used to detect deep-seated vessels in large organs such as the liver during surgeries. For diagnostic applications, decrease of anisotropy may indicate the existence of cancer in anisotropic tissues such as the white matter of the brain or the mammary gland in the breast. In this paper, we will introduce a new tri-phase induction method to drive rotating high-frequency electrical current in the tissue for the measurement of electrical conductivity anisotropy. In the measurement, three electromagnets are symmetrically placed on the tissue surface and driven by high-frequency alternative currents of 0 kHz, modulated with 1 kHz 3-phase signals. In the center area of three magnets, magnetic fields are superimposed to produce a rotating induction current. This current produces electrical potentials among circularly arranged electrodes to be used to find the conductivity in each direction determined by the electrode pairs. To find the horizontal and vertical signal components, the measured potentials are amplified by a 2ch lock-in amplifier phase-locked with the 1 kHz reference signal. The superimposed current in the tissue was typically 45 micro Amperes when we applied 150 micro Tesla of magnetic field. We showed the validity of our method by conducting in vitro measurements with respect to artificially formed anisotropic materials and preliminary in vivo measurements on the pig’s liver. Compared to diffusion tensor MRI method, our anisotropy sensor is compact and advantageous for use during surgical operations because our method does not require strong magnetic field that may disturb ongoing surgical operations.