Bruno Quesson

A gradient in the density of SR-Ca ²⁺ pumps appears from the center to the periphery of Purkinje cells (Pcells) after MI. We found that this post-MI rearrangement could result from the peripheral expression of SERCA2b pump, which is absent in healthy hearts. The additional expression of SERCA2b to the existing cardiac pump SERCA2a, and possibly more efficient Ca ²⁺ -transport properties of SERCA2b, are consistent with the proarrhythmic elevation of SR-Ca ²⁺ uptake previously proposed in Pcells after MI.

Purpose: Real‐time monitoring of microwave liver ablation (MWA) using MRI thermometry can be hindered by boiling‐induced susceptibility artifacts. These artifacts cause large temperature measurement errors that prevent accurate lesion size prediction. This study proposes a correction methodology based on removing the contribution of this susceptibility artifact using subvoxel sources of susceptibility. Methods: In vivo microwave ablations ( N = 23) were performed on seven pig livers and the temperature was monitored using the proton resonance frequency shift (PRFS) method. The boiling‐induced artifacts were observed in 11 ablation cases. To validate the proposed methodology, the thermal dose was computed from the corrected temperature maps, and the resulting lesion estimates were compared in three dimensions with ground‐truth lesion segmentations derived from post‐ablation T1w images. A numerical simulation was also conducted to emphasize the need for a finer spatial discretization. Results: After correction, a better agreement was noticed between thermal dose prediction and lesion size. Over the 11 cases observed with boiling‐induced susceptibility artifacts, the median volumetric Dice, Total Overlap, and False Negative rates changed by 4.8%, 6.2%, and −11.4%. Conclusion: Comparison with T1w imaging showed improvements in prediction of lesion volume. The proposed methodology takes into account partial volume effects and the contribution of adjacent slices. It was able to simulate a diverse range of deformed dipole‐like artifacts observed in experimental data.

Introduction: Interventional cardiac MRI in the context of the treatment of cardiac arrhythmia requires submillimeter image resolution to precisely characterize the cardiac substrate and guide the catheter-based ablation procedure in real-time. Conventional MRI receiver coils positioned on the thorax provide insufficient signal-to-noise ratio (SNR) and spatial selectivity to satisfy these constraints.Methods: A small circular MRI receiver coil was developed and evaluated under different experimental conditions, including high-resolution MRI anatomical and thermometric imaging at 1.5 T. From the perspective of developing a therapeutic MR-compatible catheter equipped with a receiver coil, we also propose alternative remote active detuning techniques of the receiver coil using one or two cables. Theoretical details are presented, as well as simulations and experimental validation.Results: Anatomical images of the left ventricle at 170 µm in-plane resolution are provided on ex vivo beating heart from swine using a 2 cm circular receiver coil. Taking advantage of the increase of SNR at its vicinity (up to 35 fold compared to conventional receiver coils), real-time MR-temperature imaging can reach an uncertainty below 0.1°C at the submillimetric spatial resolution. Remote active detuning using two cables has similar decoupling efficiency to conventional on-site decoupling, at the cost of an acceptable decrease in the resulting SNR.Discussion: This study shows the potential of small dimension surface coils for minimally invasive therapy of cardiac arrhythmia intraoperatively guided by MRI. The proposed remote decoupling approaches may simplify the construction process and reduce the cost of such single-use devices.

The tremendous advancement of cardiac imaging methods, the substantial progress in predictive modelling, along with the amount of new investigative multimodalities, challenge the current technologies in the cardiology field. Innovative, robust and multimodal tools need to be created in order to fuse imaging data (e.g., MR, CT) with mapped electrical activity and to integrate those into 3D biophysical models. In the past years, several cross-platform toolkits have been developed to provide image analysis tools to help build such software. The aim of this study is to introduce a novel multimodality software platform dedicated to cardiovascular diagnosis and therapy guidance: MUSIC. This platform was created to improve the image-guided cardiovascular interventional procedures and is a robust platform for AI/Deep Learning, image analysis and modelling in a newly created consortium with international hospitals. It also helps our researchers develop new techniques and have a better understanding of the cardiac tissue properties and physiological signals. Thus, this extraction of quantitative information from medical data leads to more repeatable and reliable medical diagnoses.

This work presents an integrated technology for assessing in vivo anticancer treatments in mice, based on various heating conditions. Bioluminescence imaging (BLI) is used to assess the physiological response of tumor and tumor microenvironment (TME) to heat treatment induced by magnetic resonance‐guided high‐intensity focused ultrasound (MRgHIFU). Transgenic tumor cells and mouse models with either constitutive or thermo‐induced luciferase expressions are combined to monitor cell viability and heat‐induced processes in the tumor and TME. BLI performed after MRgHIFU heating shows that a moderate increase in temperature (45 °C) over 5 min can be exploited to promote heat‐activable treatments in the tumor and its TME, without inducing direct cell death. A higher temperature rise over a shorter exposure time can induce cell death in the tumor, as revealed by a reduction in the BLI signal after treatment. Under these conditions, BLI also reveals that the TME can be stimulated by heat without inducing necrosis. These integrated technologies and models are useful to assess, in vivo in mice, the efficacy of various anticancer strategies exploiting local heat deposition by noninvasive MRgHIFU, including those combining tumor ablation with local drug administration using thermosensitive nanovehicles.

Characterizing myocardial activation is of major interest for understanding the underlying mechanism of cardiac arrhythmias. Electromechanical wave imaging (EWI) is an ultrafast ultrasound-based method used to map the propagation of the local contraction triggered by electrical activation of the heart. This study introduces a novel way to characterize cardiac activation based on the time evolution of the instantaneous frequency content of the cardiac tissue displacement curves. The first validation of this method was performed on an ex vivo dataset of 36 acquisitions acquired from two working heart models in paced rhythms. It was shown that the activation mapping described by spectral analysis of interframe displacement is similar to the standard EWI method based on zero-crossing of interframe strain. An average median error of 3.3 ms was found in the ex vivo dataset between the activation maps obtained with the two methods. The feasibility of mapping cardiac activation by EWI was then investigated on two open-chest pigs during sinus and paced rhythms in a pilot trial of cardiac mapping with an intracardiac probe. Seventy-five acquisitions were performed with reasonable stability and analyzed with the novel algorithm to map cardiac contraction propagation in the left ventricle (LV). Sixty-one qualitatively continuous isochrones were successfully computed based on this method. The region of contraction onset was coherently described while pacing in the imaging plane. These findings highlight the potential of implementing EWI acquisition on intracardiac probes and emphasize the benefit of performing short time-frequency analysis of displacement data to characterize cardiac activation in vivo .

Funding Acknowledgements: Type of funding sources: Other. Main funding source(s): National Research Agency (ANR) French Federation of Cardiology : “Aide à la recherche par équipe 2018, Cardiopathies de l’enfant” Introduction: After percutaneous implantation of an atrial septal defect (ASD) occluder device, a complex healing process leads to the device coverage within several months. However, an unexplained incomplete device coverage is at risk of complications such as thrombosis or infectious endocarditis. Purpose: The aim of the study was to assess the device coverage process of ASD occluder devices in a chronic sheep model using micro-CT technology. Methods: After percutaneous creation of an ASD by catheterization, 8 ewes (mean age 5.4 ± 0.7 yo and mean weight 55.6 ± 7.9 kg) were implanted with a 16-mm Nit-Occlud ASD-R occluder (PFM medical, Cologne, Germany) and were followed for 1 month (N = 3) and 3 months (N =5). After heart explantation, a iodine contrast agent was used to enhance the tissue signal. The device coverage was then assessed by micro-CT and the results were compared to histology, used as the gold standard for healing evaluation. The micro-CT image resolution was 41.7 µm. Reconstruction was performed in 2D and 3D with Amira® software, allowing to obtain images that were exploited by a code to measure the surface for each disk of the analyzed devices. Histological study was performed after resin embedding and Richardson blue staining was used. The pathologist was blinded to the duration of animals’ follow-up and micro-CT results. Results: ASD creation and device closure was successful in 100% animals without complications. Following heart explantation, macroscopic assessment of devices showed that the coverage was complete for the left-side disk regardless of the duration of the follow-up and variable for the right-side disk, depending of the protrusion of this disk. 2D and 3D micro-CT analysis allowed an accurate evaluation of device coverage of each disk and was overall well correlated to histology slices (cf Figure). Surface calculation from micro-CT images showed that the median surface of coverage was 93 ± 8% for the left-side disk and 55 ± 31% for the right-side disk. Conclusion: This preliminary study made the proof of concept that micro-CT is a reliable tool to assess the coverage of intra-cardiac occluders in vitro. The translation to clinical practice is challenging but would allow an individual follow-up, to avoid thrombotic or infective complications. Abstract Figure.