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Inductively coupled stent antennas in MRI
Author(s) -
Quick Harald H.,
Kuehl Hilmar,
Kaiser Gernot,
Bosk Silke,
Debatin Jörg F.,
Ladd Mark E.
Publication year - 2002
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.10269
Subject(s) - stent , lumen (anatomy) , biomedical engineering , radiofrequency coil , imaging phantom , electromagnetic coil , radiology , materials science , magnetic resonance imaging , medicine , surgery , physics , quantum mechanics
The development of intimal hyperplasia following stent deployment can lead to narrowing or even occlusion of the stent lumen. The underlying mechanisms leading to neointimal proliferation within stents remain largely unknown. Long‐term evaluation of stent patency requires a noninvasive means for assessing the stent lumen. MR angiography (MRA) has shown potential to provide noninvasive assessment of the vascular system. However, a detailed assessment of the stent lumen with MRI is often hampered by material‐dependent susceptibility artifacts, as well as by radiofrequency (RF) eddy currents generated inside the electrically conducting stent mesh. In this study, stent prototypes were designed to act as active resonant structures at the Larmor frequency of the MR system. Employing the principle of inductive coupling, the B 1 fields of the stents were coupled to that of an outside surface coil. The stents thus acted as local RF signal amplifiers. Various stent designs were investigated regarding their coupling to an external coil, signal homogeneity, and suitability for mechanical expansion for implantation purposes. The dependency of flip angle amplification on the quality factor Q of the stents was systematically investigated. Phantom experiments revealed signal amplification in all stent prototypes. Signal enhancement inside and close to the surface of the stents enabled their localization with high contrast in MR images. In vivo imaging experiments in the iliac, renal, and splenic arteries of two pigs confirmed the in vitro findings. Wireless active visualization of stents allows for detailed analysis of the stent lumen with high contrast and spatial resolution. The proposed method could thus provide a powerful diagnostic means for the noninvasive long‐term follow‐up of stent patency, thereby enhancing our understanding of the mechanisms of restenosis. Magn Reson Med 48:781–790, 2002. © 2002 Wiley‐Liss, Inc.