Analysis of the RF Excitation of Endovascular Stents in Small Gap and Overlap Scenarios Using an Electro-Optical E-field Sensor
Simon Reissa b, Thomas Lottnera c, Ali Çağlar Özena d e, Stefan Poleif, Andreas Bitzerg, Michael Bocka c
- aDepartment of Radiology, Medical Physics, Medical Center – University of Freiburg
- bFaculty of Medicine, University of Freiburg, Freiburg, Germany
- cFaculty of Medicine, University of Freiburg
- dGerman Consortium for Translational Cancer Research Partner Site Freiburg, German Cancer Research Center (DKFZ)
- ewith the Faculty of Medicine, University of Freiburg
- fCORTRONIK GmbH, Rostock-Warnemünde
- gInstitute of Photonics and ICT (IPI), University of Applied Sciences FHGR
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Abstract
OBJECTIVE: To assess the effect of the electro-magnetic coupling of endovascular stents on their RF heating potential in MRI. METHODS: A custom-built electro-optic E-field probe is used to perform measurements of the scattered E-field at a distance of 2 mm to stent samples with submillimeter resolution. Various combinations of stent lengths are measured at 124 MHz (3T MRI Larmor frequency) with varying gap and overlap between the stents, with and without stent coating, and with distilled water and saline solution as surrounding media. The results are compared to theoretically derived E-field distributions. RESULTS: At an overlap of 10 mm the E-field pattern of two stents collapses to a single dipole indicating excellent coupling between the stents. E-field intensities substantially increase/decrease up to 5-fold/2.5-fold if the total length of the two combined stents is closer/further away from the resonance length of the single stents. Stent coating and conductivity of the surrounding medium strongly influence the E-field patterns of overlapping stents. Measured and calculated E-field patterns are in good agreement. CONCLUSION: Electro-optic E-field measurements are a valuable tool for RF safety assessments in both single as well as coupled stents. SIGNIFICANCE: RF induced heating of single stents during MRI has been extensively studied. However, in clinical practice often two or more stents are implanted in close proximity which can substantially change the pattern of the scattered electric fields and the localization and intensity of hot spots. In this study a detailed assessment of the coupling of stents during RF excitation is given.