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On the heating of inductively coupled resonators (stents) during MRI examinations
Author(s) -
Busch Martin,
Vollmann Wolfgang,
Bertsch Thomas,
Wetzler Rainer,
Bornstedt Axel,
Schnackenburg Bernhard,
Schnorr Jörg,
Kivelitz Dietmar,
Taupitz Matthias,
Grönemeyer Dietrich
Publication year - 2005
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.20618
Subject(s) - resonator , materials science , electromagnetic coil , specific absorption rate , radiofrequency coil , q factor , restenosis , biomedical engineering , optoelectronics , stent , computer science , radiology , antenna (radio) , physics , medicine , telecommunications , quantum mechanics
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. Magn Reson Med, 2005. © 2005 Wiley‐Liss, Inc.