title: On the heating of inductively coupled resonators (stents) during MRI examinations.
abstract: Stents that have been implanted to preserve the results of vascular dilatation are frequently affected by in-stent restenosis, which ideally should be followed up by a noninvasive diagnostic modality. Active MRI stents can enable this kind of follow-up, while normal metallic stents can not. The prototype stents investigated in this study were designed as electric resonating circuits without a direct connection to the MR imager, and function as inductively coupled transmit coils. The model of a long solenoid coil is used to describe the additional power loss caused by such resonators. The theoretically estimated temperature increase is verified by measurements for different resonators and discussed for worst-case conditions. The RF power absorption of an active resonator is negligible compared to the total power absorbed during MRI. The local temperature increase observed for prototypes embedded in phantoms is in a range that excludes direct tissue damage. However, ruptures in the conducting structure of a resonator can cause hot spots, which may establish a high local temperature. This hazard can be reduced by designing resonators with a low quality (Q) factor or by setting the circuit slightly off resonance; however, this would lower the nominal amplification for which the resonator was designed.
authors.affiliation: Grönemeyer Institut für Mikrotherapie, Universität Witten/Herdecke, Bochum, Germany. busch@microtherapy.de
authors.forename: Martin
authors.initials: M
authors.lastname: Busch
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Vollmann
authors.forename: Thomas
authors.initials: T
authors.lastname: Bertsch
authors.forename: Rainer
authors.initials: R
authors.lastname: Wetzler
authors.forename: Axel
authors.initials: A
authors.lastname: Bornstedt
authors.forename: Bernhard
authors.initials: B
authors.lastname: Schnackenburg
authors.forename: Jörg
authors.initials: J
authors.lastname: Schnorr
authors.forename: Dietmar
authors.initials: D
authors.lastname: Kivelitz
authors.forename: Matthias
authors.initials: M
authors.lastname: Taupitz
authors.forename: Dietrich
authors.initials: D
authors.lastname: Grönemeyer
mesh_terms: D001807:Blood Vessel Prosthesis / Q000009:adverse effects*; D002056:Burns / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control; D003198:Computer Simulation; D004574:Electromagnetic Fields / Q000009:adverse effects; D004735:Energy Transfer; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000009:adverse effects*; D008955:Models, Cardiovascular; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000209:etiology* / Q000503:physiopathology* / Q000517:prevention & control; D011874:Radiometry; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D015607:Stents / Q000009:adverse effects*