Magnetic based micro-indentation catheter for soft tissue characterization in minimally invasive surgery

Abstract

During the last ten years, open heart surgery has increasingly been replaced by minimally invasive surgery (MIS), which has three main advantages. There is reduced blood loss, small scars to reduce infections, and a shorter recovery time. However, MIS still lacks full surgical capabilities such as tool dexterity, tool-tissue contact force determination and tissue characterization. Tissue characterization in open heart surgery is performed by palpation, but during MIS artificial tactile sensing in a catheter tip needs to be used to determine tissue abnormalities and the effectiveness of thermal ablation. Thermal ablation in the heart is used to treat atrial fibrillation (heart rhythm disease) by destroying tissue and therefore blocking an electrical pathway. The treatment effectiveness is determined by measuring the resulting increase in stiffness of the lesion, which directly relates to the size of tissue that has been burned. There are currently no solutions available for this artificial sensing. Therefore the main goal of this research is to develop a catheter tip capable of force and soft tissue stiffness measurement in the human heart. During this research, such a catheter tip has been designed. Stiffness sensing is performed based on load-displacement determination, where the catheter is actuated ex vivo by a concentric tube mechanism in a displacement-controlled mode. Contact force measurement, between the catheter tip and tissue, is performed with a 3D magnetic Hall sensor and a permanent magnet, each attached to one end of a spring (resilient structure). The design has been prototyped and tested, and is able to discriminate between different stiffness values with high repeatability.