Bioelectrical Strategies for Image-Guided Therapies

Many novel strategies now exist for the diagnosis and treatment of medical conditions from cancer to cardiac arrhythmias, however the range of guidance systems is much more limited. Therefore, the aim of this thesis is to develop two mutually-beneficial methods for guiding ablative therapy and other minimally-invasive surgeries or diagnostic tools. The first method is based on a single equivalent moving dipole model of cardiac activity, for the non-invasive and rapid detection of the site of origin of an arrhythmia from body-surface ECG signals. It provides 3-D co-ordinates of the catheter tip relative to the site of origin of the arrhythmia. The algorithm will be substantially developed to enable the guidance of an RF ablation catheter to the site of origin of the arrhythmia in an anisotropic, inhomogeneous torso. Testing will be conducted in computer simulations and in a phantom torso. These tests will examine the ability of the algorithm to accurately guide the catheter tip towards a simulated bioelectric source dipole and then to detect superposition of the catheter tip with this dipole, in the presence of systematic error. This work will serve as the foundation for the development and in-vivo testing of a full prototype guidance system.
The second guidance method develops a novel algorithm for real-time, 3-D surgical image guidance, based on the application of a finite element algorithm to an impedance map derived from MRI images. The algorithm provides 3-D absolute co-ordinates of the catheter tip. We aim to first test our method using computer simulations to assess the resolution of the algorithm and to examine the effects of anisotropy. We will then conduct phantom experiments in which the phantom?s impedance map is already known. Lastly, we will acquire MRI data of tissue phantoms and generate an impedance map from these images; this map will then be used in the guidance of an electrode through the tissue phantom.