25 March 2016 Effects of tissue heterogeneity on single-coil, scanning MIT imaging
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Abstract
We recently reported on the use of a single induction coil to accomplish imaging of the electrical conductivity in human tissues via magnetic induction tomography (MIT). A key to the method was the development of a mapping equation that quantitatively relates an arbitrary electrical conductivity distribution to ohmic loss in a coil consisting of concentric circular loops in a plane. By making multiple coil loss measurements at a number of locations in the vicinity of the target (scan), this mapping equation can be used to build an algorithm for 3D image construction of electrical conductivity. Important assumptions behind the mathematical formula included uniform relative permittivity throughout all space and continuous variation in conductivity. In this paper, these two assumptions were tested in a series of experiments involving the use of human tissue phantoms created from agarose, doped with sufficient sodium chloride to yield physiological conductivities. Inclusions of doped agarose were scanned both while isolated and also while embedded in a matrix of agarose gel having lowered conductivity - to help evaluate the effects of abrupt permittivity change. The effects of discontinuous conductivity change were simulated by filling 5 cm diameter petri dishes with 1.4% aqueous KCl and placing them in a much larger, 14 cm diameter petri dish - gap distance varied from about 3 mm to 30 mm. In either case, we will show that these effects are minimal on resultant images, helping to further validate the mapping equation used to construct MIT images. Because of their simplicity, scans reported here did not include coil rotation. To acknowledge the importance of rotation, however, we have devoted a section of this work to illustrate the profound benefits of coil rotation during a scan – though virtual data are used, where coil rotation is more easily specified.
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J. R. Feldkamp, J. R. Feldkamp, S. Quirk, S. Quirk, "Effects of tissue heterogeneity on single-coil, scanning MIT imaging", Proc. SPIE 9783, Medical Imaging 2016: Physics of Medical Imaging, 978359 (25 March 2016); doi: 10.1117/12.2216805; https://doi.org/10.1117/12.2216805
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