Efficient Non-Invasive Registration with A-mode Ultrasound in Skull Surgery

Surgical navigation is an interactive localization technique to establish a relation between surgical instruments, patient’s anatomy, and additional data (e.g. preoperative or intraoperative patient images or atlases). The first attempt to localize structures within the brain using orientation points on the skull surface and a standardized brain atlas was done at the beginning of 20th century (1908) by Sir Victor Horsley and Robert H. Clarke (Tan & Black 2002). They used a rigid frame (Horsley-Clarke apparatus) designed to measure salient points on the skull in Cartesian 3D coordinate system and transform them to the coordinate system of a brain atlas. Coordinate system computations allowed a surgeon to position a tool to a desired position within the skull. Findings of Horsley and Clarke were followed by further improvements in frame design, coordinates computations, and brain atlases. However, the major breakthrough was achieved as imaging technologies emerged, Computed Tomography (CT) in 1973 and Magnetic Resonance Imaging (MRI) during 1980s. Three-dimensional brain images allowed an extension of stereotactic computation to the entire intracranial space. Until the end of 1990s, stereotaxy has been the most common localization technique in the neurosurgery (Grunert et al. 2003). Frameless navigation emerged as an alternative to conventional stereotactic surgery, in order to decrease invasiveness and to improve localization and targeting. The main objective of image-guided surgery is to track surgical instruments in relation to the patient images. To achieve this, a geometric transformation between physical and image space has to be established in a registration procedure. First attempts to avoid invasive stereotactic frames in neurosurgical navigation emerged at the end 1980s with neuronavigator arms (Watanabe et al. 1987, Watanabe 1996, Laborde et al. 2002), sixdimensional mechanical digitizers performing point-based registration of the patient and image space and computer-based arm tracking. The main disadvantage of those systems is the need for repeated registration after each repositioning of the patient’s head (Schiffbauer 1992). Further development of digitalization system introduced magnetic (Tan et al. 1993) and optical localizers (Zamorano et al. 1992;1993) in the neuronavigation, able to interactively track instruments and patient position. Although optical tracking devices have a disadvantage of requiring permanent line-of-sight during tracking, they are currently state-of-the-art technique in surgical navigation due to a better localization accuracy O pe n A cc es s D at ab as e w w w .ite ch on lin e. co m