Towards refractive index corrected optical coherence tomography as a navigation tool for bone surgery

Optical techniques are utilized in robot aided surgery as navigation tools to guide surgical instruments. The advantages are a reduction of severe damage during surgery and of post-surgical trauma. A common approach is to place spherical markers inside the operating field, which can be detected by a 3D imaging device, in order to determine the position of the patient with respect to the instrument. Optical coherence tomography (OCT) is not only capable of detecting these kind of artificial landmarks, but also natural features within the operating field and the bone. For example, during insertion of artificial cochlear implants channels have to be drilled inside the temporal bone [1]. Air inclusions in the surrounding bone, known as mastoid cells, can be used as natural landmarks and their position has to determined with high precision (see figure 1 (left)). However, when using optical devices as navigation tool, the optical properties of biological tissue distort the three dimensional data set due to refractive index changes which have to be corrected for navigation. This has been performed in ophthalmology but has not been done so far for bone and similar materials [2].