Purpose Develop a deflectable intracardiac MR imaging (ICMRI) guiding‐sheath to accelerate imaging during MR‐guided electrophysiological (EP) interventions for radiofrequency (500 kHz) ablation (RFA) of arrythmia. Requirements include imaging at three to five times surface‐coil SNR in cardiac chambers, vascular insertion, steerable‐active‐navigation into cardiac chambers, operation with ablation catheters, and safe levels of MR‐induced heating. Methods ICMRI’s 6 mm outer‐diameter (OD) metallic‐braided shaft had a 2.6 mm OD internal lumen for ablation‐catheter insertion. Miniature‐Baluns (MBaluns) on ICMRI’s 1 m shaft reduced body‐coil‐induced heating. Distal section was a folded “star”‐shaped imaging‐coil mounted on an expandable frame, with an integrated miniature low‐noise‐amplifier overcoming cable losses. A handle‐activated movable‐shaft expanded imaging‐coil to 35 mm OD for imaging within cardiac‐chambers. Four MR‐tracking micro‐coils enabled navigation and motion‐compensation, assuming a tetrahedron‐shape when expanded. A second handle‐lever enabled distal‐tip deflection. ICMRI with a protruding deflectable EP catheter were used for MR‐tracked navigation and RFA using a dedicated 3D‐slicer user‐interface. ICMRI was tested at 3T and 1.5T in swine to evaluate (a) heating, (b) cardiac‐chamber access, (c) imaging field‐of‐view and SNR, and (d) intraprocedural RFA lesion monitoring. Results The 3T and 1.5T imaging SNR demonstrated >400% SNR boost over a 4 × 4 × 4 cm 3 FOV in the heart, relative to body and spine arrays. ICMRI with MBaluns met ASTM/IEC heating limits during navigation. Tip‐deflection allowed navigating ICMRI and EP catheter into atria and ventricles. Acute‐lesion long‐inversion‐time‐T1‐weighted 3D‐imaging (TWILITE) ablation‐monitoring using ICMRI required 5:30 min, half the time needed with surface arrays alone. Conclusion ICMRI assisted EP‐catheter navigation to difficult targets and accelerated RFA monitoring.

Objective: Cardiovascular interventional devices typically have long metallic braids or backbones to aid in steerability and pushability. However, electromagnetic coupling of metallic-based cardiovascular interventional devices with the radiofrequency (RF) fields present during Magnetic Resonance Imaging (MRI) can make a device unsafe for use in an MRI scanner. We aimed to develop MRI conditional actively-tracked cardiovascular interventional devices by sufficiently attenuating induced currents on the metallic braid/tube and internal-cabling using miniaturized resonant floating RF traps (MBaluns). Method: MBaluns were designed for placement at multiple locations along a conducting cardiovascular device to prevent the establishment of standing waves and to dissipate RF-induced energy. The MBaluns were constructed with loosely-wound solenoids to be sensitive to transverse magnetic fields created by both surface currents on the device's metallic backbone and common-mode currents on internal cables. Electromagnetic simulations were used to optimize MBalun parameters. Following optimization, two different MBalun designs were applied to MR-actively-tracked metallic guidewires and metallic-braided electrophysiology ablation catheters. Control-devices were constructed without MBaluns. MBalun performance was validated using network-analyzer quantification of current attenuation, electromagnetic Specific-Absorption-Rate (SAR) analysis, thermal tests during high SAR pulse sequences, and MRI-guided cardiovascular navigation in swine. Results: Electromagnetic SAR simulations resulted in ≈20 dB attenuation at the tip of the wire using six successive MBaluns. Network-analyzer tests confirmed ∼17 dB/MBalun surface-current attenuation. Thermal tests indicated temperature decreases of 5.9 °C in the MBalun-equipped guidewire tip. Both devices allowed rapid vascular navigation resulting from good torquability and MR-Tracking visibility. Conclusion: MBaluns increased device diameter by 20%, relative to conventional devices, providing a spatially-efficient means to prevent heating during MRI. Significance: MBaluns allow use of long metallic components, which improves mechanical performance in active MR-guided interventional devices.

Introduction: We previously demonstrated MBalun radio-frequency (RF) traps [1] that rendered metallic-backbone interventional devices MRI-conditional with only a 20% diameter increase, while preser...