Three-Dimensional Magnetic Induction Tomography: Practical Implementation for Imaging throughout the Depth of a Low Conductive and Voluminous Body
Abstract
:1. Introduction
2. Materials and Methods
2.1. Applied Techniques for 3D MIT Imaging
- Virtually perfect gradiometry was established. The receivers were aligned gradiometrically with the transmitter field; thus, almost all received signals originated in the measurement object itself [2,3]. This means that the full dynamic range of the receiver can be used for the secondary field, that is, the imprint of the test body of interest.
- Measurements were made using transmission geometry, which means that the test body was mainly located between the excitation coil and the receiver coils. Thus, the fields always passed through the entire body. This technique increased the amount of information about the interior of the body.
- Due to the rapidly blurring and decaying induction fields over distance, the geometric gap between the excitation and receiver coils was kept as small as possible. Consequently, the smallest dimension of the test body ultimately determined the required gap [8]. Preferred directions can, and should, therefore be used to facilitate MIT challenges. For example, the human torso is not normally spherical in shape.
- A Weak coupling approach was considered. The operating frequency was chosen to be so low (here: 1.5 MHz) that the induction fields would not experience significant attenuation or distortion in the weakly conducting test body. This allowed the assumption that the primary field was not affected or altered inside the body, which considerably simplified the calculation [28].
- A single, planar exciter (undulator) provided the wave-shaped primary field, which enhanced the central area sensitivity (>20 dB) together with the lateral scan procedure.
- The lateral and linear movement of the test object between the excitation coil (undulator) and the opposing receivers provided a considerable amount of independent data within 10 s. The mechanical scan was subjected to low mechanical vibration and motion artifacts.
- In forward modeling, the eddy currents in the object have to be recalculated for each position of the lateral scan method (here, 200 x-positions). However, the frequently performed, computationally expensive forward problem was significantly reduced using a sinusoidal field topology. Only two eddy current solutions had to be calculated, and the total MIT computation was accelerated by one order of magnitude [8]. This advantage required an extended undulator for only one significant spatial frequency in the x-direction. The previously applied and more compact excitation with only five strips could not provide a sufficiently clean sinusoidal field topology.
- Butterfly receivers were used instead of circular receiver coils. In comparison to a circular receiver coil, this geometry further increased the sensitivity of the dipole-shaped current fields typically originating from local perturbations in a conductive background (by about 6 dB).
- As a practical simplification, a restriction was initially made to use only voluminous cuboids with torso-like dimensions. The general functionality of the system was, however, not restricted to voluminous cuboids. Although possible, the acquisition and modeling of arbitrarily shaped bodies is more complex and initially more prone to errors.
2.2. Electro-Mechanical MIT Scanner Setup
2.3. Conductive Body Phantom
2.4. Reconstruction in the Computer
3. Experimental Results
3.1. Measurement Signal Validation
3.2. Reconstruction in 3D
4. Discussion
5. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
Appendix A
Appendix B
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Klein, M.; Erni, D.; Rueter, D. Three-Dimensional Magnetic Induction Tomography: Practical Implementation for Imaging throughout the Depth of a Low Conductive and Voluminous Body. Sensors 2021, 21, 7725. https://doi.org/10.3390/s21227725
Klein M, Erni D, Rueter D. Three-Dimensional Magnetic Induction Tomography: Practical Implementation for Imaging throughout the Depth of a Low Conductive and Voluminous Body. Sensors. 2021; 21(22):7725. https://doi.org/10.3390/s21227725
Chicago/Turabian StyleKlein, Martin, Daniel Erni, and Dirk Rueter. 2021. "Three-Dimensional Magnetic Induction Tomography: Practical Implementation for Imaging throughout the Depth of a Low Conductive and Voluminous Body" Sensors 21, no. 22: 7725. https://doi.org/10.3390/s21227725
APA StyleKlein, M., Erni, D., & Rueter, D. (2021). Three-Dimensional Magnetic Induction Tomography: Practical Implementation for Imaging throughout the Depth of a Low Conductive and Voluminous Body. Sensors, 21(22), 7725. https://doi.org/10.3390/s21227725