Imitation of radiofrequency ablation with fiber delivered laser system for magnetic resonance guided treatment of atrial fibrillation

Abstract

Atrial Fibrillation (AF) is among the most common cardiac arrhythmias with a high risk of mortality and morbidity. As a cure several minimally invasive catheter approaches are performed under imaging guidance. These treatments imitate linear and transmural cuts and sutures along the atrial walls similar to the widely accepted surgical Cox Maze procedure to block undesired currents. Catheter delivery of RF energy to the cardiac chamber is widely used and approved as safe and successful. The operation is commonly performed under X-Ray which is deprived of soft tissue contrast. Besides, combination of the image with ECG (electrocardiogram) data makes the operation technically difficult and time consuming. Due to the long exposure times, X-Ray burns may be seen on the patient. MR images can be taken during RF ablation with proper matching and tuning circuits, however, during the operation RF and ECG catheters may cause artifacts in the image for some orientations. On the other hand, fiber delivery of laser energy has no significant MR compatibility issues and can be used under MR guidance. Nevertheless, MR guided laser ablation is not in clinical practice as a minimally invasive technique for curing AF possibly because of the risk of perforating the myocardial wall. Excess light intensity at the end of the fiber tip causes rapid changes in the temperature gradients which may cause charring. This is an undesired effect and especially in cardiac ablations, light intensity should be diffused. There are several diffusing tip designs to emit light in cylindrical symmetry, but, due to their orientation with respect to the cardiac chamber, common RF delivery methods cannot be applied directly. In this thesis, we propose a novel multiple fiber laser energy delivery with catheter approach and a system that imitates the scars created with RF probes under MR guidance. The system closely imitates the ablation pattern of RF delivery and therefore is expected to have quick adaptation by physicians. As a proof of principle, we used 3 fibers oriented in different directions and obtained real time MR thermometry maps of the ex-vivo and in-vitro ablation zones during laser delivery. In addition, various light diffusion methods are considered for single fiber power delivery. We believe the combination of these methods will be the solution for the MR compatible RF laser ablation system.