Intracardiac MR imaging (ICMRI) guiding‐sheath with amplified expandable‐tip imaging and MR‐tracking for navigation and arrythmia ablation monitoring: Swine testing at 1.5 and 3T

Abstract

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 cm3 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.

Real-time cardiovascular magnetic resonance-guided radiofrequency ablation: A comprehensive review

“…Custom-made actively tracked needles (incorporated a receiver antenna) have been described to enable transseptal puncture under real-time CMR guidance[ 55 ]. Recently, a deflectable intracardiac MRI-compatible guiding-sheath was developed to accelerate imaging during CMR-guided electrophysiological interventions while real-time CMR-guided pericardiocentesis using commercially available passive access titanium needles has also been described[ 56 , 57 ].…”

Imaging of the Atria in Atrial Fibrillation Patients Using Cardiac MRI

“…41 An example of such T1w-imaging sequence is TWILITE (T1w long inversion time), which is a promising method for the acute detection of ablation lesions without the need for a contrast agent (Figure 1D). 42,43 Given the high resolution imaging that is required to visualize the thin atrial wall, techniques to enhance the signal to noise ratio of non-CAE T1w-images will be paramount for utility in clinical practice.…”

“…Schmidt and colleagues successfully executed a real-time MRI-guided ablation in the RA-and LA roof of a swine model, and subsequently performed TWILITE imaging and histological examination. 43 Visual comparison revealed that the ablation procedure created both continuous and spaced lesions. However, since lesion size was not assessed quantitatively, the reliability of TWILITE in real-time lesion evaluation could not be confirmed.…”