Enabling freehand scanning of optical coherence tomography needle probes using a magnetic tracking system

Optical coherence tomography (OCT) is an optical imaging modality that can perform real-time and in vivo imaging of biological tissue at micrometre-scale resolutions. Due to its limited imaging depth (1-2 mm) in turbid biological tissue, various forms of imaging probes have been designed to accommodate the need to image deeper into the human body, including intravascular probes for blood vessel imaging, endoscopic probes for hollow organ imaging, and needle probes, the focus of this study, for interstitial imaging of solid tissues and organs. OCT images are generated via a lateral beam scanning mechanism. Until recently, most OCT needle probes have been scanned using a motorised setup. Whilst highly accurate, the complexity of a motorized setup often makes the probe unwieldy and difficult to guide during probe deployment in a clinical environment. A more convenient approach would be to manoeuvre the needle probe by hand and perform freehand lateral scanning. The elimination of bulky scanning motors and associated electronics facilitates the development of a miniaturized handheld probe, and the high degree of freedom provided by a freehand scanning method aids in smooth control and guidance of the needle probe. However, hand motion inevitably contains variations in speed and orientation, which can result in geometric distortion in the reconstructed image if unaccounted for. Although motion tracking methods could be used to improve these artefacts, the requirement to track at the micrometre scale is not readily met by many established methods.