Interventional CMR Course
SCMR 22nd Annual Scientific Sessions
Background: Real-time MRI is a promising alternative guidance method to fluoroscopy by providing excellent soft-tissue contrast of cardiovascular anatomy without radiation exposure . However, the lack of guidewires that are compatible with the MRI environment, do not induce heating, and can be reliably visualized is a major challenge. Preclinical evaluations of new guidewire designs have been conducted at 1.5 and 3T . Here we further evaluate 3T MRI-guided cardiovascular catheterization using a novel glass-fiber based MR guidewire in phantoms and porcine models in terms of safety, device visualization, and procedural time.
Experiments were performed in a 3T MRI scanner (Prisma, Siemens) using a 0.035” glass-fiber based guidewire (MaRVis Interventional GmbH)  and a 7Fr Arrow Balloon Wedge Pressure Catheter without MR artifact. First, to evaluate safety, lead tip heating (LTH) induced by the guidewire was measured in an ASTM torso phantom . Fluoroptic thermal probes (Lumasense Technologies) were placed within 2mm of the guidewire tip in 3 locations (Fig. 1a). To ensure maximum RF-induced LTH, we used level 1 operating mode (whole body SAR ≤ 4W/kg) with a turbo spin echo sequence (TR:137ms, FA:180°) for 5 minutes. Maximum temperature change near the guidewire was compared with background temperature change.
Real-time MRI-guided catheterization from the femoral artery to the left ventricle (LV) was performed in 5 swine. Imaging parameters are specified in Table 1. Operator 1 (O1) performed the catheterization in the MRI room using an in-room projector displaying real-time images. Operator 2 (O2) interactively selected the imaging plane during the scan. In step 1, O1 introduced the guidewire up to the catheter tip and placed them 2-5cm into the right femoral artery. In step 2, O1 pushed the guidewire into the descending aorta (Fig.1b) and O2 started the imaging. In step 3, O1 steered the guidewire across the aortic arch (Fig.1c). In step 4, O1 advanced the guidewire and the catheter across the aortic valve into the LV (Fig.1d). Procedure times for step 2-3 and step 4 (Figs.1b-c and 1d)were recorded separately. Guidewire visualization was assessed by measuring the dimensions of the signal void (Fig.1e) and CNR between the signal void and blood.
Results: In the phantom experiments, no LTH over 0.5°C was observed (Table 2a), showing the guidewire safety at 3T. The catheter was successfully placed in the LV under real-time MRI for all swine. The procedure times are shown in Table 2b. A learning curve was observed and time stabilized in the last 3 experiments. The CNR and signal void dimensions are shown in Table 2b. No significant image distortion was observed.
Conclusion: This pilot swine study shows that real-time 3T MRI-guided cardiovascular catheterization using a new glass-fiber based MR guidewire is feasible and has favorable safety. We acknowledge the funding from NIH K25 HL135408 and the Radiological Sciences Department at UCLA.