Advances in Real-Time MRI–Guided Electrophysiology

Fig. 1. Interventional MRI (iCMR) set-up to perform electrophysiology (EP) procedures. An example set-up for an animal (porcine) study is shown here. The electrophysiologist can view both electrical and imaging data on dedicated displays. A foot switch can be used to start/stop MRI scanning in the same way as during fluoroscopy-guided procedures. Subject monitoring (Invivo, Gainesville, Florida): four-lead surface ECG, arterial blood pressure monitoring and oxygen saturation assessment are available and can be viewed both inside the scanner room and control room. MR-compatible electrophysiology catheters are connected to a tracking interface which can transmit tracking data to the image guidance platform. Radiofrequency (RF) generator, irrigation pump and EP recording system are located within the control room

Fig. 2. Recording surface ECG and intra-cardiac EGMs inside a MRI scanner. Significant distortions inside a MRI scanner can occur on both the surface ECG and during intra-cardiac EGM acquisition due to (1) time-varying MR gradient fields, (2) RF pulses during MR scanning that couple to conductive material (a) and (3) magneto-hydrodynamic (MHD) voltages due to the static magnetic field (b). Noise filtering technologies are required to improve intra-cardiac EGM fidelity and reduce baseline noise (c, d)

Fig. 3. Passive catheter tracking with negative contrast using a spoiled gradient echo sequence in coronal orientation with a water-selective excitation pulse as a catheter is advanced through the aorta (a, b). Arrows show location of electrodes on a hexa-polar catheter

Fig. 4. Active catheter tracking using a MR-compatible catheter with gold-tip electrodes and two 2.5-mm solenoid receive coils (a). Using a dedicated tracking sequence, the X, Y and Z coordinates of the catheter micro-coils can be determined in 3D space (b) whilst the catheter tip can be displayed as a red icon in three orthogonal MRI projections to guide a MR-EP procedure (c)

Fig. 5. Image guidance software platforms for procedure visualisation have been developed by several MRI vendors that are capable of displaying 3D volume roadmaps, real-time imaging planes, cardiac chamber segmentations, electroanatomical maps and actively tracked catheters. Shown here are example screenshots from the Siemens iCMR platform (a) during MRI-guided electroanatomical mapping of the left ventricle in a porcine infarct model and Philips iSuite platform (b) during MRI-guided catheter ablation of the cavotricuspid isthmus in a patient with atrial flutter. (Panel b adapted from Chubb et al. JACC Clinical Electrophysiology 2017: 3; 89–103, with permission from Elsevier) [20••]. LV left ventricle, IVC inferior vena cava, MPR multi-plane reconstruction

Fig. 6. Real-time assessment of ablation lesions using MR-thermometry (a) with corresponding temperature profiles (b). (Reproduced with permission from Mukherjee et al. Europace 2018 Sep 1;20(FI2):f254-f262. doi: 10.1093/europace/eux341; Creative Commons user license https://creativecommons.org/licenses/by/4.0/) [32].