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Electrophysiological simulations of the atria could improve diagnosis and treatment of cardiac arrhythmia, like atrial fibrillation or flutter. For this purpose, a precise segmentation of both atria is needed. However, the atrial epicardium and the electrophysiological structures needed for electrophysiological simulations are barely or not at all detectable in CT-images. Therefore, a model based segmentation of only the atrial endocardium was developed as a landmark generator to facilitate the registration of a finite wall thickness model of the right and left atrial myocardium. It further incorporates atlas information about tissue structures relevant for simulation purposes like Bachmann’s bundle, terminal crest, sinus node and the pectinate muscles. The correct model based segmentation of the atrial endocardium was achieved with a mean vertex to surface error of 0.53 mm for the left and 0.18 mm for the right atrium respectively. The atlas based myocardium segmentation yields physiologically correct results well suited for electrophysiological simulations.

The delineation of anatomical structures in medical images can be achieved in an efficient and robust manner using statistical anatomical organ models, which has been demonstrated for an already considerable set of organs, including the heart. While it is possible to provide models with sufficient shape variability to cope, to a large extent, with inter-patient variability, as long as object topology is conserved, it is a fundamental problem to cope with topological organvariability. We address this by creating a set of model variants and selecting the most appropriate model variant for the patient at hand. We propose a hybrid method combining model-based image analysiswith a guided region growing approach for automated anatomical variant selection and apply it to the left atrium in cardiac CT images. Concerning the human heart, the left atrium is the most variable sub-structure with a variable number of pulmonary veins drainng into it.It is of large clinical interest in the context of atrial fibrillation and related interventions.

Background: Percutaneous cardiac interventions are currently performed under X-ray guidance. Magnetic resonance imaging has been employed to guide intravascular interventions in the past, but mainly in animals. Translation of MR-guided interventions into humans has been limited by the lack of fully MR-compatible and safe devices, such as MR guidewires with mechanical characteristics similar to standard guidewires. The aim of the present study was to evaluate the safety and efficacy of a newly developed MR-safe and compatible passive guidewire in aiding MR-guided cardiac interventions in a swine model and describe the two first-in-man solely MR-guided interventions. Methods and Results: In the preclinical trial, the new MR compatible wire aided the performance of 20 interventions in 5 swine. These consisted of balloon dilation of nondiseased pulmonary and aortic valves, aortic arch and branch pulmonary arteries. Catheter manipulations were monitored with real time MRI sequence with interactive modification of imaging plane and slice position. Following ethics and regulatory authority approval the two first-in-man MR-guided interventions were performed in a child and an adult, both with elements of valvar pulmonary stenosis. Both patients had successful relief of the valvar stenosis and were discharged home a few hours later with no complications. Conclusions: The described pre-clinical study and case reports are encouraging that with the availability of the new MR compatible and safe guidewire, certain percutaneous cardiac interventions will become feasible to perform solely under MR-guidance. The benefits are clear with elimination of the use of ionising radiation and improvement of visualisation of the target lesions.