Abstract
The sensitivity gain of ultrahigh field Magnetic Resonance (UHF-MR) holds the promise to enhance spatial and temporal resolution. Such improvements could be beneficial for cardiovascular MR. However, intracoronary stents used for treatment of coronary artery disease are currently considered to be contra-indications for UHF-MR. The antenna effect induced by a stent together with RF wavelength shortening could increase local radiofrequency (RF) power deposition at 7.0 T and bears the potential to induce local heating, which might cause tissue damage. Realizing these constraints, this work examines RF heating effects of stents using electro-magnetic field (EMF) simulations and phantoms with properties that mimic myocardium. For this purpose, RF power deposition that exceeds the clinical limits was induced by a dedicated birdcage coil. Fiber optic probes and MR thermometry were applied for temperature monitoring using agarose phantoms containing copper tubes or coronary stents. The results demonstrate an agreement between RF heating induced temperature changes derived from EMF simulations versus MR thermometry. The birdcage coil tailored for RF heating was capable of irradiating power exceeding the specific-absorption rate (SAR) limits defined by the IEC guidelines by a factor of three. This setup afforded RF induced temperature changes up to +27 K in a reference phantom. The maximum extra temperature increase, induced by a copper tube or a coronary stent was less than 3 K. The coronary stents examined showed an RF heating behavior similar to a copper tube. Our results suggest that, if IEC guidelines for local/global SAR are followed, the extra RF heating induced in myocardial tissue by stents may not be significant versus the baseline heating induced by the energy deposited by a tailored cardiac transmit RF coil at 7.0 T, and may be smaller if not insignificant than the extra RF heating observed under the circumstances used in this study.
Highlights
The sensitivity gain and signal-to-noise ratio (SNR) advantages inherent to ultrahigh field (B07.0 Tesla) Magnetic Resonance (MR) hold the promise to enhance spatial and temporal resolution in MR imaging (MRI) [1,2]
Intracoronary stents commonly used in percutaneous interventions – a revascularization procedure for treatment of acute and chronic coronary artery disease (CAD) [10,11,12] - are currently considered to be contraindications for MRI using magnetic field strengths of 7.0 T and higher
The results demonstrate an agreement between RF heating induced temperature changes derived from electro-magnetic field (EMF) simulations versus temperature maps deduced from MR thermometry at 7.0 T and the measurements with the fiber optic system
Summary
The sensitivity gain and signal-to-noise ratio (SNR) advantages inherent to ultrahigh field (B07.0 Tesla) Magnetic Resonance (MR) hold the promise to enhance spatial and temporal resolution in MR imaging (MRI) [1,2] Such improvements could fuel a number of cardiovascular MR (CMR) applications, including the characterization of ischemic and inflammatory disorders on the myocardial tissue level, mapping myocardial microstructure and parametric imaging [3,4,5,6,7,8,9]. The antenna effect due to the presence of implants with high conductance in conjunction with the decrease in RF wave lengths and the increase in RF energy may cause RF power deposition at ultrahigh fields that may induce local heating [22,23] and may potentially cause myocardial tissue damage, influence coagulation or affect endothelial function
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
