Vascular Image Guidance to Aid Endovascular Treatments

Schwalbe, Marius (2018). Vascular Image Guidance to Aid Endovascular Treatments. (Dissertation, University of Bern, Faculty of Medicine)

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Endovascular procedures have become an important minimal invasive treatment option for various pathologies. They range from the percutaneous transluminal angioplasty, to the treatment of malformations, all the way to the transarterial embolization of liver tumors. However, endovascular procedures require extensive training and sufficient experience to minimize complications and associated morbidity. As they are typically carried out using 2D fluoroscopy for orientation and guidance within the vascular system, the loss of the depth dimension hinders the spatial perception and thus further increases the mental workload for the interventionalist. Moreover, accurate needle and catheter placement involves multiple procedural steps, which are performed under constant fluoroscopic guidance by means of ionizing radiation and high doses of contrast agent to visualize the target vessels.
The aim of this thesis is the integration of stereotactic image guidance into the clinical workflow for vascular treatments to reduce the radiation dose as well as the amount of contrast agent, the former not only for the patient but also for the interventionalist. We are mainly interested in understanding how a navigation system can be seamlessly integrated into the clinical workflow of endovascular treatments, without adding supplemental complexity due to the navigation itself (e.g. due to explicit registration or calibration steps). Various approaches based on different imaging modalities, as well as different tracking technologies (optical and electromagnetic) are investigated.
For the treatment of congenital vascular malformations two navigation approaches based on electromagnetic and optical tracking respectively were investigated. During a pre-clinical validation, a MRI-based image guidance approach using optical tracking was compared to the conventional approach in a technical phantom. The results suggested that stereotactic navigation may lead to a reduction in overall intervention time and radiation dose (n = 90 targeting attempts carried out by three interventionalists).
Additionally, an approach for the targeting of liver tumors based on an endovascular intrahepatic electromagnetic reference were studied. Instead of an explicit registration process, it utilizes a simple 3D offset measurement from 2D fluoroscopy images. During preliminary experiments a major influence of the C-arm on the electromagnetic tracking accuracy was revealed, while the proposed offset measurement was confirmed to be feasible (mean error 0.76 mm). In an ex vivo porcine liver evaluation, the overall feasibility was confirmed (mean target positioning error of 2.0 mm). Furthermore, the evaluation of the proposed technique for a combined ablation and transarterial chemoembolization treatment of HCCs in a single session in an animal study (6 pics, n = 512 targeting attempts) confirmed the approach to be accurate (mean target positioning error of 2.9 ± 1.6 mm) and efficient (14 ± 8 seconds mean time for tumor targeting).
Currently a clinical pilot study for the evaluation of the MRI-based image guidance approach for congenital vascular malformation treatment is ongoing (6 patients enrolled until the end of October 2017) at the University Hospital of Bern. A preliminary analysis of the data shows successful targeting of the malformation in a single attempt in 75% during 16 punctures.

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