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

Content Provider	IEEE Xplore Digital Library
Author	Rahlves, M. Diaz Diaz, J. Thommes, J. Majdani, O. Roth, B. Ortmaier, T. Reithmeier, E.
Copyright Year	2013
Description	Author affiliation: Clinic for Laryngology, Rhinology &Otology, Hannover Med. Sch., Hannover, Germany (Majdani, O.) \|\| Hannover Center for Opt. Technol., Leibniz Univ. Hannover, Hannover, Germany (Rahlves, M.; Roth, B.; Reithmeier, E.) \|\| Inst. of Mechatron. Syst., Leibniz Univ. Hannover, Hannover, Germany (Diaz Diaz, J.; Thommes, J.; Ortmaier, T.)
Abstract	Summary form only given. 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].In this contribution, we present a strategy to correct OCT data for refractive index changes in bone. The correction was carried out with in vitro measurements of porcine temporal bone which were obtained by using a swept source OCT (OCS1300SS) of Thorlabs, Inc. To gain information on the optical properties of the specimen, we prepared a 1 mm thick bone sample with planar and parallel surfaces. The refractive index was determined from OCT scans normal to the bone boundaries according to [3] and was found to be 1.51 ± 0.02. In this work, it was assumed that the bone is a homogeneous material which is a valid assumption in a statistical average. Before refractive index correction, we carried out a geometrical calibration of the OCT, as described in [4], which provides information about the optical path of the OCT's scanning beam in free space. For correction, we determined the incidence angle of the scanning beam with respect to the air-bone boundary and performed the refractive correction by applying Snell's law and linear scaling of the optical path with the refractive index. The performance of the correction was tested first at OCT scans of a water droplet on a microscope cover slide (see figure 1 (middle)) and afterwards at a porcine bone sample with marker holes on the upper and lower surface. We found that the image distortion which accounts for more than 100 μm can be significantly reduced by our correction algorithm.
Sponsorship	Eur. Phys. Soc.
Starting Page	1
Ending Page	1
File Size	319341
Page Count	1
File Format	PDF
e-ISBN	9781479905942
DOI	10.1109/CLEOE-IQEC.2013.6801526
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2013-05-12
Publisher Place	Germany
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Biomedical optical imaging Optical distortion Optical imaging Optical variables control Bones Adaptive optics Optical refraction
Content Type	Text
Resource Type	Article

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