volume | PIER Journals

Abstract

This study describes the techniques and signal properties of a large, powerful, and linear-scanning 1.5 MHz induction field scanner. The mechanical system is capable of quickly reading the volume of relative large objects, e.g., a test person. The general approach mirrors Magnetic Induction Tomography (MIT), but the details differ considerably from currently-described MIT systems: the setup is asymmetrical, and it operates in gradiometric modalities, either with coaxial excitation with destructive interference or with a single excitation loop and tilted receivers. Following this approach, the primary signals were almost completely nulled, and test objects' real or imaginary imprint was obtained directly. The coaxial gradiometer appeared advantageous: exposure to strong fields was reduced due to destructive interference. Meanwhile, the signals included enhanced components at higher spatial frequencies, thereby obtaining a gradually improved capability for localization. For robust signals, the excitation field can be powered towards the rated limits of human exposure to time-varying magnetic fields. Repeated measurements assessed the important signal integrity, which is affected by the scanner´s imperfections, particularly any motions or respiratory changes in living beings during or between repeated scans. The currently achieved and overall figure of merit for artifacts was 58 dB for inanimate test objects and 44 dB for a test person. Both numbers should be understood as worst case levels: a repeated scan with intermediate breathing and drift/dislocations requires 50 seconds, whereas a single measurement (with respiratory arrest) takes only about 5 seconds.

1. Wei, H. and M. Soleimani, "Electromagnetic tomography for medical and industrial applications: Challenges and opportunities [Point of view]," Proceedings of the IEEE, Vol. 101, No. 3, 559-565, 2013.
doi:10.1109/JPROC.2012.2237072 Google Scholar

2. Dekdouk, B., C. Ktistis, D. Armitage, and A. Peyton, "Absolute imaging of low conductivity material distributions using nonlinear reconstruction methods in magnetic induction tomography," Progress In Electromagnetics Research, Vol. 155, 1-18, 2016.
doi:10.2528/PIER15071705 Google Scholar

3. Wei, H. and M. Soleimani, "Hardware and software design for a national instrument-based magnetic induction tomography system for prospective biomedical applications," Physiological Measurement, Vol. 33, No. 5, 863-879, 2012.
doi:10.1088/0967-3334/33/5/863 Google Scholar

4. Scharfetter, H., S. Issa, and D. Gursoy, "Tracking of object movements for artefact suppression in Magnetic Induction Tomography (MIT)," Journal of Physics: Conference Series, Vol. 224, 012040, 2010.
doi:10.1088/1742-6596/224/1/012040 Google Scholar

5. Zolgharni, M., H. Griffiths, and P. Ledger, "Frequency-difference MIT imaging of cerebral haemorrhage with a hemispherical coil array: Numerical modelling," Physiological Measurement, Vol. 31, No. 8, S111-S125, 2010.
doi:10.1088/0967-3334/31/8/S09 Google Scholar

6. Gursoy, D. and H. Scharfetter, "Reconstruction artefacts in magnetic induction tomography due to patient’s movement during data acquisition," Physiological Measurement, Vol. 30, No. 6, S165-S174, 2009.
doi:10.1088/0967-3334/30/6/S11 Google Scholar

7. Watson, S., R. Williams, W. Gough, and H. Griffiths, "A magnetic induction tomography system for samples with conductivities below 10 Sm⁻¹," Measurement Science and Technology, Vol. 19, No. 4, 045501, 2008.
doi:10.1088/0957-0233/19/4/045501 Google Scholar

8. Rosell-Ferrer, J., R. Merwa, P. Brunner, and H. Scharfetter, "A multifrequency magnetic induction tomography system using planar gradiometers: Data collection and calibration," Physiological Measurement, Vol. 27, No. 5, S271-S280, 2006.
doi:10.1088/0967-3334/27/5/S23 Google Scholar

9. Vauhkonen, M., M. Hamsch, and C. Igney, "A measurement system and image reconstruction in magnetic induction tomography," Physiological Measurement, Vol. 29, No. 6, S445-S454, 2008.
doi:10.1088/0967-3334/29/6/S37 Google Scholar

10. Wei, H. and M. Soleimani, "Three-dimensional magnetic induction tomography imaging using a matrix free krylov subspace inversion algorithm," Progress In Electromagnetics Research, Vol. 122, 29-45, 2012.
doi:10.2528/PIER11091513 Google Scholar

11. Wei, H. and M. Soleimani, "Four dimensional reconstruction using magnetic induction tomography: Experimental study," Progress In Electromagnetics Research, Vol. 129, 17-32, 2012.
doi:10.2528/PIER12032403 Google Scholar

12. Wei, H., L. Ma, and M. Soleimani, "Volumetric magnetic induction tomography," Measurement Science and Technology, Vol. 23, No. 5, 055401, 2012.
doi:10.1088/0957-0233/23/5/055401 Google Scholar

13. Wei, H. and M. Soleimani, "Two-phase low conductivity flow imaging using magnetic induction tomography," Progress In Electromagnetics Research, Vol. 131, 99-115, 2012.
doi:10.2528/PIER12070615 Google Scholar

14. Ma, L., H. Wei, and M. Soleimani, "Planar magnetic induction tomography for 3D near subsurface imaging," Progress In Electromagnetics Research, Vol. 138, 65-82, 2013.
doi:10.2528/PIER12110711 Google Scholar

15. Wei, H. and M. Soleimani, "Theoretical and experimental evaluation of rotational magnetic induction tomography," IEEE Transactions on Instrumentation and Measurement, Vol. 61, No. 12, 3324-3331, 2012.
doi:10.1109/TIM.2012.2205516 Google Scholar

16. Dekdouk, B., C. Ktistis, W. Yin, D. Armitage, and A. Peyton, "The application of a priori structural information based regularization in image reconstruction in magnetic induction tomography," Journal of Physics: Conference Series, Vol. 224, 012048, 2010.
doi:10.1088/1742-6596/224/1/012048 Google Scholar

17. Ktistis, C., D. Armitage, and A. Peyton, "Calculation of the forward problem for absolute image reconstruction in MIT," Physiological Measurement, Vol. 29, No. 6, S455-S464, 2008.
doi:10.1088/0967-3334/29/6/S38 Google Scholar

18. Rosell, J., R. Casanas, and H. Scharfetter, "Sensitivity maps and system requirements for magnetic induction tomography using a planar gradiometer," Physiological Measurement, Vol. 22, No. 1, 121-130, 2001.
doi:10.1088/0967-3334/22/1/316 Google Scholar

19. Morris, A., H. Griffiths, and W. Gough, "A numerical model for magnetic induction tomographic measurements in biological tissues," Physiological Measurement, Vol. 22, No. 1, 113-119, 2001.
doi:10.1088/0967-3334/22/1/315 Google Scholar

20. Scharfetter, H., P. Riu, M. Populo, and J. Rosell, "Sensitivity maps for low-contrast perturbations within conducting background in magnetic induction tomography," Physiological Measurement, Vol. 23, No. 1, 195-201, 2002.
doi:10.1088/0967-3334/23/1/320 Google Scholar

21. International commission on non-ionizing radiation protection (ICNIRP): Guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields (up to 300 GHz), published at www.icnirp.org. Google Scholar

22. IFA Report 3/2017, Grenzwerteliste 2017, , Sicherheit und Gesundheitsschutz am Arbeitsplatz, published at www.dguv.de. Google Scholar

23. HeidaryDastjerdi, M., D. Ruter, O. Kanoun, and J. Himmel, "Induktionsfelder mit vorteilhaften Topologien in der Magnetischen-Induktions-Tomografie," TM --- Technisches Messen, Vol. 80, No. 11, 2013. Google Scholar

24. Good, R., "Elliptic integrals, the forgotten functions," European Journal of Physics, Vol. 22, No. 2, 119-126, 2001.
doi:10.1088/0143-0807/22/2/303 Google Scholar

25. Scharfetter, H., R. Merwa, and K. Pilz, "A new type of gradiometer for the receiving circuit of Magnetic Induction Tomography (MIT)," Physiological Measurement, Vol. 26, No. 2, S307-S318, 2005.
doi:10.1088/0967-3334/26/2/028 Google Scholar

26. Hollaus, K. J., C. Magele, R. Merwa, and H. Scharfetter, "Fast calculation of the sensitivity matrix in magnetic induction tomography by tetrahedral edge finite elements and the reciprocity theorem," Physiological Measurement, Vol. 25, No. 1, 159-168, 2004.
doi:10.1088/0967-3334/25/1/023 Google Scholar

27. Griffith, H., W. Gough, S. Watson, and R. J. Williams, "Residual capacitive coupling and the measurement of permittivity in magnetic induction tomography," Physiological Measurement, Vol. 28, No. 7, S301-311, 2007.
doi:10.1088/0967-3334/28/7/S23 Google Scholar

28. Faes, T. J. C., H. A. van der Meij, J. C. de Munck, and R. M. Heethaar, "The electric resistivity of human tissues (100 Hz–10 MHz): A meta-analysis of review studies," Physiological Measurement, Vol. 20, No. 4, R1-10, 1999.
doi:10.1088/0967-3334/20/4/201 Google Scholar

29. Rueter, D., H. P. Hauber, D. Droemann, P. Zabel, and S. Uhlig, "Low frequency ultrasound permeates the human lung in situ: A novel method for lung testing," Ultraschall in Med., Vol. 31, No. 1, 53-62, 2010.
doi:10.1055/s-0028-1109482 Google Scholar

30. Gursoy, D. and H. Scharfetter, "Imaging artifacts in magnetic induction tomography caused by the structural incorrectness of the sensor model," Measurement Science and Technology, Vol. 22, No. 1, 1-10, 2011.
doi:10.1088/0957-0233/22/1/015502 Google Scholar

Dr. Martin Klein

Dr. Dirk Rueter