Validation of Thermometric Cardiac Imaging by MRI

Resumo breve

Radiofrequency ablation is the primary treatment for atrial and ventricular arrhythmias resistant to medication. However, the absence of assessment of injury creation during radiofrequency application is an important issue. One of the objectives of the Institut Hospitalo-Universitaire (IHU) Liryc (l'Institut de Rythmologie et Modélisation Cardiaque) is to improve ablation procedures by radiofrequency of cardiac arrhythmias. This is based on thermometric imaging by Magnetic Resonance Imaging (MRI) which allows a real time visualization of tissue temperature in all the myocardium with sufficient spatial and temporal resolution to characterize the induced thermal lesion. Today, investigators have developed and validated a new method for cardiac thermometry, associating rapid MRI acquisition technique (4 to 5 slices per heart beat) with online image reconstruction and correction algorithms against residual motion, magnetic susceptibility, drift of the magnetic field, etc... Recent preclinical studies showed a precision of 1°Celsius in the myocardium, largely sufficient to characterize a thermal treatment induced by radiofrequency where typical temperature rises of 40°C are observed during ablation. Temporal evolution of the temperature in each pixel provides access to calculation of the accumulated thermal dose that is a relevant indicator of the induced necrosis. This imaging method must now be evaluated in humans in order to test its robustness under real conditions (presence of arrhythmias, corpulent patients, etc…) and to optimize acquisition parameters and image processing. The aim of this research is thus to obtain specific MRI sequence of images of patients, on which will be evaluated the different algorithms of reconstruction and processing for temperature imaging. This study is a mandatory step in the perspective of future clinical treatments of cardiac arrhythmia under MRI.