This thesis describes the electrical and physiological characterization of cardiac tissue with myocardial infarction (MI) responsible for abnormal cardiac rhythms such as ventricular tachycardia (VT), using a newly-developed magnetic resonance imaging (MRI) electrophysiology system. In electrophysiology (EP), radiofrequency (RF) catheter ablation combined with cardioverter-defibrillator implantation is a first-line action to manage ventricular VT. Unfortunately, this therapy is known to have sub-optimal success rates in a large number of patients because of difficulties to accurately identifying the arrhythmic target regions. Currently, characterization of post-MI scars is performed by using catheters to measure electrical signals of the endocardial tissue (electroanatomical mapping), under x-ray fluoroscopy guidance. Prolonged radiation exposure to both the cardiologist and the patient have made the use of MRI extremely attractive; further, unlike x-ray imaging, MRI provides post-MI scars with direct visualization, characterization in three dimensions and the ability to visualize ablation lesions. Although recent research has focused on registration between pre-acquired MR images and electroanatomical maps, a potentially more useful approach is to use real-time MRI to directly locate and characterize potential arrhythmogenic regions during the EP procedure. A real-time MR-guided EP system was developed and validated to perform EP diagnostic procedures, such as mapping and pacing. In a series of animal studies, the system demonstrated the ability to use active catheter tracking and intra-procedural MR imaging to navigate to specific regions in the left ventricle and record intracardiac electrical signals. A study correlating myocardial fibrotic scar detected by multicontrast late enhancement (MCLE) MRI and electroanatomical voltage mapping demonstrated that MRI information (transmurality, tissue classification, and relaxation rate) can accurately predict areas of myocardial fibrosis identified with bipolar voltage mapping. Finally, MCLE-derived gray zone was shown to have a high correspondence to regions with a high proportion of abnormal intracardiac signals. The methods described in this thesis help advance the understanding of infarcted tissue responsible for ventricular tachycardia. Further studies are proposed to perform RF ablation lesions and correlate pre- and post-ablation tissue electrophysiological properties with MRI.

This thesis describes the electrical and physiological characterization of cardiac tissue with myocardial infarction (MI) responsible for abnormal cardiac rhythms such as ventricular tachycardia (VT), using a newly-developed magnetic resonance imaging (MRI) electrophysiology system. In electrophysiology (EP), radiofrequency (RF) catheter ablation combined with cardioverter-defibrillator implantation is a first-line action to manage ventricular VT. Unfortunately, this therapy is known to have sub-optimal success rates in a large number of patients because of difficulties to accurately identifying the arrhythmic target regions. Currently, characterization of post-MI scars is performed by using catheters to measure electrical signals of the endocardial tissue (electroanatomical mapping), under x-ray fluoroscopy guidance. Prolonged radiation exposure to both the cardiologist and the patient have made the use of MRI extremely attractive; further, unlike x-ray imaging, MRI provides post-MI scars with direct visualization, characterization in three dimensions and the ability to visualize ablation lesions. Although recent research has focused on registration between pre-acquired MR images and electroanatomical maps, a potentially more useful approach is to use real-time MRI to directly locate and characterize potential arrhythmogenic regions during the EP procedure. A real-time MR-guided EP system was developed and validated to perform EP diagnostic procedures, such as mapping and pacing. In a series of animal studies, the system demonstrated the ability to use active catheter tracking and intra-procedural MR imaging to navigate to specific regions in the left ventricle and record intracardiac electrical signals. A study correlating myocardial fibrotic scar detected by multicontrast late enhancement (MCLE) MRI and electroanatomical voltage mapping demonstrated that MRI information (transmurality, tissue classification, and relaxation rate) can accurately predict areas of myocardial fibrosis identified with bipolar voltage mapping. Finally, MCLE-derived gray zone was shown to have a high correspondence to regions with a high proportion of abnormal intracardiac signals. The methods described in this thesis help advance the understanding of infarcted tissue responsible for ventricular tachycardia. Further studies are proposed to perform RF ablation lesions and correlate pre- and post-ablation tissue electrophysiological properties with MRI.

Thermoablationsverfahren werden in der klinischen Routine zur Therapie bei Patienten mit primären Lebertumoren und Lebermetastasen eingesetzt, bei denen von einer Operation abgesehen wird. Die laserinduzierte Thermotherapie (LITT) ist ein minimal invasives radiologisches Verfahren zur perkutanen Tumorablation. Mit der Magnetresonanztomographie (MRT) am Hochfeldtomographen (1.5 Tesla) steht eine radiologische Methode mit der Option einer präzisen Prozesskontrolle der Thermoablation und einer suffizienten Erfolgskontrolle zur Verfügung. Ziel dieser Arbeit war es, im Tierexperiment die Anwendung der LITT zur Ablation von Pankreasgewebe zu erproben, das Potenzial der MRT für die Prozesskontrolle der LITT am Pankreas zu bestimmen und neue MRT-Sequenzen mit neuen Kontrastmitteln für die Optimierung der Erfolgskontrolle zu erforschen. Die LITT am Pankreas im Rahmen einer Pilotstudie an 15 Läuferschweinen war perkutan komplikationsarm durchführbar, generalisierte Pankreatitiden oder Blutungen traten nicht auf. Die qualitative Prozessbeobachtung mittels thermosensitiver Sequenzen zeigte eine hohe Übereinstimmung zwischen magnetresonanztomographisch dokumentierten Thermoeffekten und histopathologisch verifizierten thermisch induzierten Nekrosen. Die Untersuchung und invasive Kalibrierung verschiedener Messmethoden in vivo zur quantitativen MRT-Thermometrie ergab Vorteile für den Einsatz der Protonenresonanzfrequenz-Methode. Zur Optimierung der Erfolgskontrolle nach LITT von Lebergewebe im Tierexperiment sowie klinisch bei Lebermetastasen wurden die MRT-Kontrastmittel Gadomesoporphyrin, Eisenoxid und Gadobutrol erprobt. Mittels Spätaufnahmen 6 - 18 h post injectionem wurden mit Gadobutrol thermisch induzierte Nekrosen präzise visualisiert. / Thermoablation of primary liver tumors and liver metastases is widely used in patients without surgical options. The laser-induced thermotherapy (LITT) is a minimal invasive radiologic procedure for percutaneous tumor ablation. With high field magnetic resonance imaging at 1.5, monitoring of thermoablation and visualization of thermal induced ablation zones can be performed precisely. Aim of this work was to investigate the feasibility of MR-guided LITT of pancreatic tissue and to optimise the contrast between thermal induced lesions, residual tumor and normal tissue after LITT procedure. MR-guided LITT was feasible in 15 female pigs, generalized pancreatitis or bleeding did not occur. MR monitoring by thermosensitive sequences precisely visualized thermal induced ablation zones verified by histopathologic examination. Best results of MR thermometry (thermo-mapping) were obtained by proton resonance frequency method. Gadolinum- mesoporphyrine, superparamagnetic iron oxides (SPIO) and gadobutrol were used to optimise ablation control. Late enhanced imaging 6 - 18 hours after injection of gadobutrol precisely visualized thermal induced necrosis. In conclusion, percutaneous MR guided LITT of pancreatic tissue of female pigs was feasible and monitoring of thermoablation could be performed accurately. In contrast to other imaging methods, MR using new contrast agents enables accurate visualization of thermal induced necrosis.