High resolution CARdiac MRI-thermometry on a clinical scanner using intracardiac COils – CARCOI

Software has been developed to simulate 3D magnetic field maps generated by a coil of any shape. The electronic circuits and their frequency response have been modeled using open source software. These two tools make it possible to test and predict the operation of several sensor configurations in order to optimize their design before they are built. Safety aspects were integrated into this phase, in particular to deactivate/reactivate the sensor synchronously with the energy emissions from the MRI system during each MRI measurement. With this in mind, a theoretical analysis of the behavior of MRI antennas was carried out. Each prototype designed was characterized on an electronic test bench and then interfaced with a 1.5T clinical MRI. The signal-to-noise ratio was quantified on test samples and compared to that of commercial antennas under the same experimental conditions to determine the gain.

Several MRI acquisition methods were implemented, along with the associated image reconstruction algorithms, and then integrated into a real-time image processing chain dedicated to MRI thermometry. An original thermometry method was implemented to map any undesirable heating of medical devices during MRI image acquisition, enabling the safety of a device inserted into the body to be assessed under real conditions. A final catheter demonstrator incorporating a deployable MRI detector was built using the technical capabilities offered by the Bioengineering platform at the IHU liryc. The imaging capabilities were evaluated in the final phase of the project.

The results of the prototype characterizations performed on an electrical test bench are in very good agreement with the numerical simulations and theoretical analysis. A new system for synchronously deactivating/reactivating the sensor with the energy emissions from the MRI system during each MRI measurement has been developed and patented. It is located remotely from the deployable MRI sensor so that it can be positioned outside the body, thereby ensuring the patient's electrical safety. This reduces the number of electronic components and lowers manufacturing costs (multiple reuse). A sensitivity gain of approximately 35 has been achieved compared to the manufacturer's detectors. The spatial resolution of fast MRI thermometry has been improved by a factor of 8, while also improving its accuracy by a factor of 5. We obtained anatomical images of the beating heart with a spatial resolution of 0.17x0.17x1.5 mm, a performance unattainable with the manufacturer's antennas in clinical settings, allowing visualization of the vascular microarchitecture of the myocardium.

We have developed an original method of rapid MRI thermometry incorporating an RF transmission module with adjustable power to simulate any MRI acquisition sequence and measure potential heating around the catheter. Several catheter prototypes incorporating a deployable MRI antenna have been designed, requiring optimization of materials (shape memory, dimensions, MRI compatibility, etc.) to produce a final functional demonstrator (active decoupling, no heating) with excellent performance (sensitivity, spatial selectivity). Several high-resolution 3D anatomical imaging and thermometry methods have been implemented, improving measurement reliability and treatment safety. These methods have not been evaluated with an intracardiac catheter because the demonstrator was finalized after the development of these imaging methods.

The prospects for this project are to resolve a few remaining technological obstacles and ensure the device is watertight before considering a possible industrial transfer of the technologies developed. Once these stages have been completed, the temperature and anatomical imaging methods developed in this project will need to be evaluated pre-clinically.

Atrial Fibrillation (AF) affects 750 000 people in France and is expected to increase 2.5 fold by 2050. In patients presenting persistent AF, the extent and locations of the arrhythmogenic substrate are highly variable. The success rate of catheter-based radiofrequency ablation procedures is in this population lower than in paroxysmal AF patients. If Magnetic Resonance Imaging (MRI) helps delivering the appropriate amount of energy to the tissue and thereby reduces arrhythmia recurrence and redo ablation procedures by 20%, this will translate into an improved patient treatment and several millions euros savings every year for the healthcare system.

To achieve these goals, the consortium will develop expandable intra-cardiac MRI receiver coils embedded into a catheter in order to increase the signal to noise ratio in the region of interest and preserve or increase image quality. The spatial selectivity of local detector will be exploited to produce ultra-high resolution anatomical and temperature images of the heart in vivo on a clinical MRI scanner (1.5T). This project also requires the development of specific 2D/3D rapid MRI thermometry acquisition methods and associated real-time reconstruction algorithms (including motion compensation) to reach such a spatial resolution and to improve precision of temperature measurement. The instrumentation and imaging methods developed will also benefit to imaging the cardiac substrate underlying arrhythmias with unparalleled spatial resolution.

This project is a breakthrough in improving the catheter-based treatment of cardiac arrhythmias by developing innovative instrumentation and optimized magnetic resonance imaging methods. It has a strong potential of major technology improvements (unexampled performances of MRI as compared to current state of-the-art) and industrial valorization (to open new medical applications of mini invasive therapies and their associated markets), together with a high societal impact (more efficient treatment, reduction of healthcare costs) and reinforced visibility and attractivity for the members of the consortium.