Rotational magnetic induction tomography

Abstract

In magnetic induction tomography (MIT), an array of excitation coils is typically used to apply time-varying magnetic fields to induce eddy currents in the material to be studied. The magnetic fields from the eddy currents are then detected by an array of sensing coils to form an image of passive electromagnetic properties (i.e. conductivity, permittivity and permeability). Increasing the number of transmitters and receivers can provide a better image quality at the expense of a larger and more expensive MIT system. Instead of increasing the number of coils, this study investigates the possibility of rotating a single transmit-receive coil to image the electrical properties of the sample, by emulating an array of 200 transmit-receive coils by time-division multiplexing. Engineering details on the electromechanical design and development of a rotating MIT system are presented. The experimental results indicate that representative images of conductive samples can be obtained at 5 MHz by rotating a single transmit-receive coil.

Three-Dimensional Magnetic Induction Tomography: Practical Implementation for Imaging throughout the Depth of a Low Conductive and Voluminous Body

“…For this reason, the practical implementation of 3D MIT has been considered here for the first time, to detect and localize perturbations throughout the depth of a weakly conductive ("biomedical") test body. With the exciter and receiver geometries previously used [3][4][5][6][7][13][14][15][16][17][18][19][20][21][22][23], the sensitivity in the central areas of a weakly conductive body is critically low [3][4][5][6][7]. In addition to the attenuation and blurring of the induction field over distance, there is another effect that further reduces the sensitivity at the center of the body: the induced eddy currents run in closed loops within the body, and the current density thus tends to be strongest near the surface, but decreases toward the center region (and along the axis of the coils), where it vanishes and no longer provides any information [8].…”

“…The perturbations were either placed close to the surface of the test body; were centered but breaking through the lower and upper surface of a shallow bath (a quasi-2D setup) while being partly isolated from the conductive background by plastic containers; were not immersed in a conductive background; or were not weakly conductive, but instead metallic. Usually, the perturbations had a relative volume (RV) from 3% to 8% of the total volume of the body [6,15,18], which corresponds to a rather poor resolution. In addition, the measurement sequence typically required more than a few seconds, thus causing the method to be uncomfortable or even unfeasible for living beings, especially because of the high susceptibility of MIT to motion artifacts [26].…”

A Special Phase Detector for Magnetic Inductive Measurement of Cerebral Hemorrhage

“…By adopting the LabVIEW quadrature demodulator, the phase noise of the system can reach 7.5 m°, whereas its phase drift is no more than 120 m° within 6 hours. In Trakic’s rotational MIT system [15] , the data collection and phase calculation were completed in an FPGA development board. Wuliang Yin et al [16] , [17] used an FPGA-based digital phase measurement method in all of their studies and obtained favorable results.…”

Comparing and improving techniques for conductivity image reconstruction in MIT: A simulation study

“…Some MIT research groups have used other forms of the induced voltage. 8,[18][19][20][21][22][23][24] Some of them [18][19][20] have used the quadrature component (imaginary part) of an induced voltage ratio, and some other groups 8,[21][22][23][24] have used the phase shift of the induced voltage in low-contrast conductivity applications, especially in biomedical applications. Yazdanian and Jafari 25 have shown these forms fall in the first above category, that is, utilizing the imaginary part of an induced voltage ratio and the phase shift of the induced voltage are equivalent to using the in-phase component (real part) of the induced voltage.…”

“…In References 42 and 43, both real and imaginary parts of the induced voltage have been applied while permeability, permittivity, or both together with conductivity have been used in the forward model and they have been estimated in the inverse problem. Some MIT research groups have used other forms of the induced voltage 8,18‐24 . Some of them 18‐20 have used the quadrature component (imaginary part) of an induced voltage ratio, and some other groups 8,21‐24 have used the phase shift of the induced voltage in low‐contrast conductivity applications, especially in biomedical applications.…”