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Towards MR-guided EP interventions using an RF-safe approach

Introduction

Various cardiac arrhythmias, e.g. atrial fibrillation and ventricular tachycardia, can be treated by electrophysiological (EP) interventions [1]. Applying MR for guiding these interventions offers advantages like 3D visualization of the cardiac soft tissue in relation to the catheter and absence of ionizing radiation [2]. In this work, a prototype MR-EP system and catheter for diagnostic EP-interventions is described, which integrates concepts for RF-safe MR-tracking [3] and EP diagnostics [4]. The operation of the system is demonstrated in MR-guided EP experiments in pigs including mapping and pacing. RF-safety of the diagnostic MR-EP catheter prototype is shown and signal quality is compared to conventional EP catheters.

Materials and methods

System setup

All experiments were performed on a clinical whole-body 1.5 T MR scanner (Achieva I/T, Philips Healthcare, Netherlands) equipped with an in-room display and an additional MR-EP-workstation (MR-EP-WS) including a standard EP-recorder (EP Tracer, CardioTek, Netherlands). This workstation, located next to the scanner, combines and displays incoming real-time 2D and 3D images and real-time tracking positions from the MR scanner as well as real-time EP-data from the EP-recorder.

A 7F diagnostic EP catheter (Fig. 1) with two ring electrodes and a tracking coil was used. Intracardiac and tracking signals are transferred via RF-safe high resistance wires [2] and a transformer-based transmission line [3], respectively.

Figure 1
figure1

Diagnostic RF-safe MR-EP catheter.

Comparison MR-EP/conventional EP catheter

Conventional diagnostic EP catheters (Supreme Quad, JSN, 5F, St Jude, MN) and MR-EP catheters were compared under X-ray. Bipolar intracardiac electrograms (IEGM) were acquired with both catheters at corresponding locations (RA lateral wall, RV apex, TV ring, and HIS).

In-vivo proof of RF-safety

Temperature recordings during a typical real-time bFFE sequence (TR 2.4 ms, flip 65°, global SAR 4 W/kg) were performed for the MR-EP and the conventional EP catheter. The catheters were equipped with fiber optic temperature probes and were inserted into the RA.

EP-Mapping procedure

The RA and RV were mapped using the MR-EP system and catheters. 3D bFFE and 3D CE-MRA datasets were acquired prior to catheterization of the animals. All MR and EP data can be combined and displayed on the MR-EP-WS for guidance, including a surface model of the cardiac vessels, reformatted slices at the catheter position either manually angulated or using the real-time MR imaging geometry.

Results

Comparison with conventional EP catheter

IEGMs acquired with the MR-EP catheter were equivalent in quality to those acquired with the conventional EP catheter (Fig. 2).

Figure 2
figure2

EP signals acquired in the RV (a) with the MR-EP catheter equipped with highly resistive wires and (b) with the conventional catheter.

In-vivo proof of RF-safety

The MR-EP catheter's maximal temperature increase after 10 min of RF transmission at 4 W/kg was 0.7 K (Fig. 3a) almost corresponding to the expected increase in global body temperature (0.6 K). Hence, device-related local heating effects are negligible.

Figure 3
figure3

In-vivo temperature increase (a) with the MR-EP catheter and (b) with the conventional catheter.

In contrast, an increase of up to 7.5 K in only 80 s was observed at the tip of the conventional catheter (Fig. 3b).

EP recording under MRI

The MR-EP-WS enabled a fast mapping, e.g. 40 points in RV in 20 min. The in-bore IEGM recordings were comparable to those under X-ray (Fig. 4).

Figure 4
figure4

Top : Roadmap-based real-time 3D-visualization of the catheter position during recording (red dot) on the MR-EP workstation. The yellow dots in the 3D rendering of the heart indicate previous mapping positions. Bottom: In-bore EP recordings at two selected positions showing an atrial signal (left) and a ventricular signal (right).

Furthermore, atrial and ventricular pacing was achieved via the MR-EP catheters. Successful stimulation was confirmed by a second MR-EP catheter and was also clearly visible in the surface ECG.

Conclusion

Recording of intracardiac electrograms is feasible with the MR-EP catheter. EP data quality is equivalent to conventional EP catheters. The combined use of highly resistive wires and a transformer-based transmission line for active tip tracking effectively suppresses RF-heating even during high SAR MRI.

The prototype setup of the MR-EP system provided excellent guidance and an efficient workflow for diagnostic MR-EP interventions.

References

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Correspondence to Sascha Krueger.

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Open Access This article is published under license to BioMed Central Ltd. This is an Open Access article is distributed under the terms of the Creative Commons Attribution 2.0 International License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Krueger, S., Lips, O., David, B. et al. Towards MR-guided EP interventions using an RF-safe approach. J Cardiovasc Magn Reson 11, O84 (2009). https://doi.org/10.1186/1532-429X-11-S1-O84

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Keywords

  • Catheter
  • Fiber Optic Temperature
  • Intracardiac Electrogram
  • Prototype Setup
  • Tracking Coil