Guidance of medical instruments based on tracking systems

CURRENTLY two-dimensional (2D) fluoroscopy and conventional digital subtraction
angiography are the gold standard for the navigation of medical instruments in many
minimal-invasive interventions like the endovascular aneurysm repair (EVAR) proce-
dures. However, this imaging-based guidance has several drawbacks: It relies on X-rays, contrast agent is used to visualize the current vessel volume and no depth information is available. A three-dimensional (3D) guidance method without these disadvantages would be ideal for the physicians. For these reasons, tracking systems as fiber optical sensors (FOS) and electromagnetic (EM) tracker are promising technologies [149, 46].
The key hypothesis of the PhD work is that a tracking-based guidance of medical instruments is possible and that it facilitates the navigation in minimal invasive interventions. Different approaches for a 3D guidance based on tracking systems will be presented in this work. The evaluated use case will be the navigation of a stent graft during an EVAR procedure.
First, an analysis and optimization of a fiber optical shape sensing (FOSS) model is conducted: The usage of an optical fiber with fiber Bragg gratings (FBGs) allows measuring the shape of a medical tool. Here, methods from literature are introduced, analyzed, compared, improved and evaluated in different experiments. The accuracy of the obtained optimized shape sensing model is evaluated with different 3D measurements. Then, novel tracking-based guidance methods are introduced: The combination of an optical fiber with FBGs and EM sensors allows determining the located shape of medical instruments. For this purpose, a spatial calibration method for an optical fiber and EM sensors is introduced. Moreover, the methods for obtaining the located shape using three or two EM sensors are described. Also utilizing additional information from preoperative data allows a guidance approach with an optical fiber and only one EM sensor. The guidance methods have been evaluated in different experiments and compared with an image-based 3D shape localization approach.
In addition, the developed approaches are applied in order to guide a stent graft in EVAR procedures. A spatial calibration between stent graft and tracking system and a suitable visualization of the guidance information are described. This stent graft guidance method is evaluated by conducting an EVAR procedure on a torso phantom. The accuracy of the stent graft was evaluated and the stent graft guidance was used for navigating, placing and correctly implanting a stent graft.