First clinical evaluation of real-time cardiac MR thermometry
Valéry Ozenne1, Solenn Toupin1,2, Pierre Bour1, Baudouin Denis de Senneville3, Alexis Vaussy2, Matthieu Matthieu Lepetit-Coiffé2, Pierre Jaïs1,4, Hubert Cochet1,4, and Bruno Quesson1

1Institut Hospitalier Universitaire : LIRYC Institut de Rythmologie et Modélisation Cardiaque, Bordeaux, France, 2Siemens France, Saint Denis, France, 3Mathematical Institute of Bordeaux, Bordeaux, France, 4Centre Hospitalier Universitaire de Bordeaux, Bordeaux, France

Synopsis

Catheter ablation using radiofrequency is commonly used to treat cardiac arrhythmia. However, direct assessment of lesion formation with MRI thermometry during RF delivery may improve safety and efficiency of the therapeutic procedure. Despite recent studies demonstrating the feasibility on volunteers or animal models, there are no reports regarding the possibility of doing cardiac thermometry on patient in the context of arrhythmias. The purpose of the present study was to evaluate the uncertainty of temperature estimate on patients depicting potential arrhythmic episodes, which may alter the precision of the method relying on an ECG-triggered acquisition.

Target audience

Researchers in interventional MRI and physicians with interest in temperature imaging and MR guided cardiovascular catheterization

Background:

Catheter ablation using radiofrequency (RF) is commonly used to treat cardiac arrhythmia. However, direct assessment of lesion formation with MRI thermometry during RF delivery may improve safety and efficiency of the therapeutic procedure. A recent study reported reliable thermometry on the heart of healthy volunteers and on large animal model during RF ablation by combining ECG-triggered rapid imaging (EPI with GRAPPA) and online correction of respiratory motion and associated susceptibility artifacts1. The purpose of the present study was to evaluate the uncertainty of temperature estimate on patients depicting potential arrhythmic episodes, which may alter the precision of the method relying on an ECG-triggered acquisition.

Method:

Patients: the study was approved by the Institutional Review Board and all subjects (N=5, 63.2 +/- 13 years old and 80.0% male) gave written informed consent. 3 subjects were in sinus rhythm and did not show substantial variations of the RR duration during scanning, whereas 2 patients displayed irregular rhythm. MR Imaging: 4 to 5 temperature slices in coronal orientation were acquired sequentially at each heart beat during approximately 3’30 minutes on a 1.5 T clinical imaging system (Avanto, Siemens Healthcare) while patients were under free breathing. The sequence was a single shot gradient echo planar imaging (TE=20ms, TR=85ms) with 110x110 voxels corresponding to a 1.6x1.6x3mm3 voxel size. Image reconstruction, correction of residual in-plane respiratory motion and associated susceptibility variations, compensation of spatial-temporal drift and low pass temporal filtering (Butterworth filter) were implemented in the Gadgetron framework2, as previously described1,3, ensuring online visualization of temperature images. To assess the precision of cardiac MR-thermometry, the temporal standard deviation of temperature (TSD) was computed in each pixel from all slices during the interventional procedure. The distribution of TSD values was analyzed on a manually drawn ROI surrounding the ventricle (Fig. 1).

Results:

Example of temperature maps are shown for subject #3 (Fig.1). For all slices, most of the pixels within the ROI surrounding the left ventricle displayed a TSD below 2°C, with a mean value of 1.18°C. Table 1 summarizes the preliminary results obtained on the 5 patients. Similar TSD (spatial mean ± standard deviation over the ROIs) values were observed for all patients, irrespective of their cycle duration variations during the acquisition period. Similar dimensions of the volumes covered by this MR thermometry sequence was obtained for each patient.

Discussion and Conclusion:

This study presents the first evaluation of cardiac MR-thermometry on patients during free-breathing. Under the tested conditions on a limited number of patients, the precision of temperature estimate was found of sufficient quality to monitor catheter-based RF ablation procedures using ECG-gated multi-slice fast thermometry acquisition and dedicated real-time image processing pipeline.

Acknowledgements

No acknowledgement found.

References

1 Ozenne V et al. Proc. ISMRM. 2014; Toronto. 2 Hansen MS, Sørensen TS. MRM 2013;69:1768–1776. 3 de Senneville B.D et al. IEEE Transactions on Medical Imaging, 2015;34:974-982

Figures

Figure 1: Magnitude images (top row) and corresponding color-coded TSD maps (bottom row). Dotted lines on magnitude images show contours of the ROI surrounding the left ventricle used for statistical analysis of temperature data (see table 1).

Table 1: Results obtained from patients indicating the RR duration and TSD measured over the ROI surrounding the myocardium covering all slices. The last two columns indicate the volume in mm3 covered by this ROI and the number of slices acquired during each RR intervals.



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
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