A radiofrequency field (RF) field exists inside body tissue during magnetic resonance imaging (MRI). If any implanted medical device is present, there can be a very intense concentration of the scattered RF field in the tissue surrounding certain parts of the implant. This causes tissue heating that can reach dangerous levels. Scattered field considerations show that it is possible to neglect the loading effect of the implant on the MR RF source. This leads to an incident field simplification. The presence of the implant in nonhomogeneous tissue increases the complexity of the scattering problem. An approach is presented that makes the computational problem considerably smaller. A method of moments (MoM) formulation of the electromagnetic model is presented. The relevant issues that arise during a finite element method (FEM) formulation are also discussed. The methods are illustrated by solving the problem for a typical implant using MoM as well as FEM.
2. Jin, J. M., J. Chen, W. C. Chew, H. Gan, R. L. Magin, and P. J. Dimbylow, "Computation of electromagnetic fields for high-frequency magnetic resonance imaging applications," Phys. Med. Biol., Vol. 41, 2719-2738, 1996.
3. Mohsin, S. A., N. M. Sheikh, and W. Abbas, "MRI induced heating of artificial bone implants," Journal of Electromagnetic Waves and Applications, Vol. 23, No. 5--6, 799-808, 2009.
4. Mohsin, S. A., N. M. Sheikh, and U. Saeed, "MRI-induced heating of deep brain stimulation leads," Phys. Med. Biol., 5745-5756, 2008.
5. Mohsin, S. A., U. Saeed, J. Nyenhuis, and N. M. Sheikh, "Interaction of the RF field with stent devices during diagnostic and interventional magnetic resonance imaging," USNC/URSI National Radio Science Meeting, San Diego, CA, USA, Jul. 5--12, 2008.
6. Nyenhuis, J. A., S. M. Park, R. Kamondetdacha, A. Amjad, F. G. Shellock, and A. Rezai, "MRI and implanted medical devices: Basic interactions with an emphasis on heating," IEEE Trans. Device and Materials Reliability, Vol. 5, No. 3, Sep. 2005.
7. Yeung, C. J., R. C. Susil, and E. Atalar, "RF safety of wires in interventional MRI: Using a safety index," Magnetic Resonance in Medicine, Vol. 47, 187-193, 2002.
8. Shellock, F. G., "Magnetic resonance safety update 2002: Implants and devices," Journal of Magnetic Resonance Imaging, Vol. 16, 485-496, 2002.
9. Mohsin, S. A., N. M. Sheikh, and U. Saeed, "MRI induced heating of deep brain stimulation leads: Effect of the air-tissue interface," Progress In Electromagnetics Research, Vol. 83, 81-91, 2008.
10. Amjad, A., "Specific absorption rate during magnetic resonance imaging,", Ph.D. Thesis, Purdue University, 2007.
11. Park, S.-M., R. Kamondetdacha, and J. A. Nyenhuis, "Calculation of MRI-induced heating of an implanted medical lead wire with an electric field transfer function," Journal of Magnetic Resonance Imaging, Vol. 26, 1278-1285, 2007.
12. Balanis, C. A., Advanced Engineering Electromagnetics, John Wiley & Sons, ,N.Y., 1989.
13. Harrington, R. F., Field Computation by Moment Methods, Wiley-Interscience and IEEE Press Series on Electromagnetic Wave Theory, 1993.
14. Harrington, R. F., Time-harmonic Electromagnetic Fields, No. 3, New York, McGraw-Hill, 1961.
15. Rumsey, V. H., "Reaction concept in electromagnetic theory," Phys. Rev., Vol. 94, No. 6, 1483-1491, 1954.
16. Volakis, J. L., A. Chatterjee, and L. C. Kempel, Finite Element Method for Electromagnetics, The IEEE/OUP Series on Electromagnetic Wave Theory, 1998.
17. Jin, J. M., The Finite Element Method in Electromagnetics, 2nd Ed., John Wiley and Sons, 2002.
18. Mohsin, S. A., N. M. Sheikh, F. Mahmood, and W. Abbas, "General considerations regarding scattering of the MRI RF field by implanted medical devices," Pakistan Journal of Engineering and Applied Sciences, Vol. 6, 17-25, Jan. 2010.
19. Khalatbari, S., D. Sardari, A. A. Mirzaee, and H. A. Sadafi, "Calculating SAR in two models of the human head exposed to mobile phones radiations at 900 and 1800 MHz," PIERS Online, Vol. 2, No. 1, 104-109, 2006.
20. Ibrahiem, A., C. Dale, W. Tabbara, and J. Wiart, "Analysis of the temperature increase linked to the power induced by RF source," Progress In Electromagnetics Research, Vol. 52, 23-46, 2005.
21. Kouveliotis, K. and C. N. Capsalis, "Prediction of the SAR level induced in a dielectric sphere by a thin wire dipole antenna," Progress In Electromagnetics Research, Vol. 80, 321-336, 2008.
22. Kuo, L.-C., Y.-C. Kan, and H.-R. Chuang, "Analusis of a 900/1800-MHz dual-band gap loop antenna on a handset with proximate head and hand model," Journal of Electromagnetic Waves and Applications, Vol. 21, No. 1, 107-122, 2007.