MRI-Induced Tissue Heating at Metallic Sutures (Cerclages)

Norbert Leitgeb, Gerhard Loos, Franz Ebner

Institute of Health Care Engineering with European Notified Body of Medical Devices, Graz University of Technology, Graz, Austria.
University Clinic of Radiology, Medical University of Graz, Graz, Austria..

DOI: 10.4236/jemaa.2013.59056                

Abstract

Magnetic resonance imaging (MRI) has become an important diagnostic tool with an ongoing dynamic development towards application of increasing static magnetic flux densities and consequently, exposures to electromagnetic fields (EMF) of increasing radio frequencies (RF). This raises particular concern metallic implants could lead to excess tissue heating and consequently, to thermal tissue damage. In thorax surgery the intersected sternum is reconnected by metallic sutures (cerclages). To investigate whether patients with such implants can be accepted for MRI and whether there may be limitations with regard to static magnetic fields, by numerical anatomical and thermal modelling MRI induced tissue heating was assessed for magnetic flux densities 1.5 T, 3 T, 4 T and 7 T. Results show that overall tissue temperature increased with increasing RF EMF frequency. However, even for setting MRI exposure parameters at maximum permissible level partial body heating remained marginally affected and even at local level the additional contribution of the presence of the metallic cerclage remained below 1°C. This allows concluding that from a heating point of view metallic sutures as used to fix the sternum after thorax surgery are no contraindication for MRI with static magnetic flux densities up to 7 T.

Keywords

Metallic Implants; Health Risk; Tissue Damage; Safety; Radio Frequency Electromagnetic Fields

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	A. Gill and F. G. Shellock, “Assessment of MRI Issues at 3-Tesla for Metallic Surgical Implants: Findings Applied to 61 Additional Skin Closure Staples and Vessel Ligation Clips,” Journal of Cardiovascular Magnetic Resonance, Vol. 9, No. 14, 2012, p. 3.
[2]	H. Virtanen, J. Keshvari and R. Lappalainen, “Interaction of Radio Frequency Electromagnetic Fields and Passive Metallic Implants—A Brief Review,” Bioelectromagnetics, Vol. 27, No. 6, 2006, pp. 431-439. doi:10.1002/bem.20224
[3]	A. Watanabe, T. Seguchi, J. Aoyama, T. Miyahara, Y. Kakizawa and K. Hongo, “Investigation of Radiofrequency-Induced Temperature Elevation of Aneurysm Clips in a 3.0-Tesla Magnetic Resonance Environment,” Neurosurgery, Vol. 61, No. 5, 2007, pp. 1062-1065. doi:10.1227/01.neu.0000303202.69747.d2
[4]	H. Graf, G. Steidle and F. Schick, “Heating of Metallic Implants and Instruments Induced by Gradient Switching in a 1.5-Tesla Whole-Body Unit,” Journal of Magnetic Resonance Imaging, Vol. 26, No. 5, 2007, pp. 1328-1333. doi:10.1002/jmri.21157
[5]	R. W. Gray, W. T. Bibens and F. G. Shellock, “Simple Design Changes to Wires to Substantially Reduce MRIInduced Heating at 1.5 T: Implications for Implanted Leads,” Magnetic Resonance Imaging, Vol. 23, No. 8, 2005, pp. 887-891. doi:10.1016/j.mri.2005.07.005
[6]	H. Bassen, W. Kainz, G. Mendoza and T. Kellom, “MRIInduced Heating of Selected Thin Wire Metallic Implants—Laboratory and Computational Studies—Findings and New Questions Raised,” Minimally Invasive Therapy and Allied Technologies, Vol. 15, No. 2, 2006, pp. 76-84. doi:10.1080/13645700600640931
[7]	E. Mattei, M. Triventi, G. Calcagnini, F. Censi, W. Kainz, G. Mendoza, H. I. Bassen and P. Bartolini, “Complexity of MRI Induced Heating on Metallic Leads: Experimental Measurements of 374 Configurations,” BioMedical Engineering OnLine, Vol. 3, 2008, pp. 7-11.
[8]	F. G. Shellock, L. N. Meepos, M. R. Stapleton and S. Valencerina, “In Vitro Magnetic Resonance Imaging Evaluation of Ossicular Implants at 3 T,” Otology & Neurotology, Vol. 33, No. 5, 2012, pp. 871-877. doi:10.1097/MAO.0b013e318254ef13
[9]	H. Muranaka, T. Horiguchi, S. Usui, Y. Ueda, O. Nakamura and F. Ikeda, “Dependence of RF Heating on SAR and Implant Position in a 1.5 T MR System,” Magnetic Resonance in Medical Sciences, Vol. 6, No. 4, 2007, pp. 199-209. doi:10.2463/mrms.6.199
[10]	A. Christ, W. Kainz and E. G. Hahn, “The Virtual Family—Development of Surface-Based Anatomical Models of Two Adults and Two Children for Dosimetric Simulations,” Physics in Medicine and Biology, Vol. 55, No. 2, 2010, pp. N23-N38. doi:10.1088/0031-9155/55/2/N01
[11]	C. Gabriel, S. Gabriel and E. Corthout, “The Dielectric Properties of Biological Tissues: I. Literature Survey,” Physics in Medicine and Biology, Vol. 41, No. 11, 1996, pp. 2231-2249. doi:10.1088/0031-9155/41/11/001
[12]	S. Gabriel, R. Lau and C. Gabriel, “The Dielectric Properties of Biological Tissues: II. Measurements in the Frequency Range 10 Hz to 20 GHz,” Physics in Medicine and Biology, Vol. 41, No. 11, 1996, pp. 2251-2269. doi:10.1088/0031-9155/41/11/002
[13]	S. Gabriel, R. Lau and C. Gabriel, “The Dielectric Properties of Biological Tissues: III. Parametric Models for the Dielectric Spectrum of Tissues,” Physics in Medicine and Biology, Vol. 41, 1996, pp. 2271-2293. doi:10.1088/0031-9155/41/11/003
[14]	N. Leitgeb, “The Impact of Thermal Modeling on Limiting RF-EMF,” Journal of Electromagnetic Analysis and Applications, Vol. 5, No. 4, 2013, pp. 137-144. doi:10.4236/jemaa.2013.54022
[15]	H. H. Pennes, “Analysis of Tissue and Arterial Blood Temperatures in the Resting Human Forearm,” Journal of Applied Physiology, Vol. 1, No. 2, 1948, pp. 93-122.
[16]	CENELEC, “Medical Electrical Equipment. Part 2-33: Particular Requirements for Basic Safety and Essential Performance of Magnetic Resonance Equipment for Medical Diagnosis,” EN 60601-2-33, CENELEC, Brussels, 2008.
[17]	ICNIRP, “Amendment to the ICNIRP Statement on Medical Magnetic Resonance (MR) Procedures: Protection of Patients,” Health Physics, Vol. 97, No. 3, 2009, pp. 259-261. doi:10.1097/HP.0b013e3181aff9eb
[18]	ICNIRP, “Medical Magnetic Resonance (MR) Procedures: Protection of the Patient,” Health Physics, Vol. 87, No. 2, 2004, pp. 197-216. doi:10.1097/00004032-200408000-00008
[19]	B. N. Taylor and C. E. Kuyatt, “Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results,” NIST Technical Note 1297, US Department of Commerce, Washington, 1994.
[20]	R. Findlay and P. Dimbylow, “Variations in Calculated SAR with Distance to Perfectly Matched Layer Boundary for a Human Voxel Model,” Physics in Medicine and Biology, 2006, Vol. 51, No. 23, pp. 411-415. doi:10.1088/0031-9155/51/23/N02
[21]	CST Studio Suite 2009, “CST GmbH, Bad Nauheimer-Straße 19, D-64289,” Darmstadt, 2013. www.cst.com