HOW DO INTERVENTIONISTS NAVIGATE TO THE TUMOURS

T.Studeli(1), D.kalkofen(2) and A.Freudenthal(1)

Faculty Industrial Design Engineering Delft University of Technology, Landbergstraat 15, 2628 CE Delft, The Netherlands

Institute fo Computer graphics and Vision, Graz University of Technology, A-8010, Graz, Austria

e-mail: t.p.studelil@tudelft.nl

www.ariser.info and www.io.tudelft.nl/

Abstract

During percutaneous radiofrequency ablation of tumours in liver (RFA procedure), interventionists place a needle with an electrode into the abdomen and directly in the tumour. Once the needle is placed in the tumour, an electrode in the needle dissipates radiofrequency waves and destroys the surrounding tissues. An importnat success factor of this minimally invasive medical procedure is the accuracy of the needle placement. Placement and insertion o the needle into the tumour are executed with the aid of medical imaging (image-guided surgery or inerventional radiology). For image guidance real-time ultra sonography (US) technology and more recently intra-operative computer tomography (CT) are commonly used. Future medical mixed-reality systems will combine those two technologies and will also allow new image modalities for intra-operative use. Th eEuropean research training network "Augmented Reality in Surgery" aims to support interventionists with "super vision" (e.g. combined US-CT) and "super sense" (e.g. haptic support for the needle insertion). herefore a prototype of a mixed-reality system running on a liver phantom has been developed The prototype presents fused US- and CT-technology. To support the design of the system the selection and use of information out of the different image modalities is investigated (user-medical imaging interactions).

This paper describes the first results from interviews and video guided cognitive walkthroughs with two experts in US- and CT-guided radiofrequency ablation of liver tumours. The data have been analysed to understand navigation behaviour and situational awareness of the interventionists during placement and insertion of the needle. The paper describes two exemplary user behaviours that aim for a safe and accurate ablation in an efficient way. The interventionist ceates in the preoperative stage a mental model of the liver as well as orientation and nevigation strategies for the positioning of the needle. He distinguishes landmarks or familiar regions - areas with special characteristics (e.g. tissue structures, cysts), and control points - characteristics that help to determine directions (e.g. legaments, vessels, bile duct). This mental model is then used in the intra-operative stage where the interventionist constantly updates his mental map (orientation and navigation) and intervention plan (action).

These findings help to design an intuitive presentation of medical information during placement and insertion of the needle (intra-operative stage). They support the design of the user interfaces and form the basis of further experimental evaluation of the system. Future research will focus on information presentation and visual load.

Keywords

Image guided intervention, Wayfinding, Situational awareness, Radio frequency ablation, Needle placement