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Session: Poster session II
Session starts: Thursday 24 January, 16:00

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Arjo Loeve (Technische Universiteit Delft)
Jenny Dankelman (Technische Universiteit Delft)
Paddy French (Technische Universiteit Delft)

Abstract:
INTRODUCTION Optical Coherence Tomography (OCT) is increasingly being applied in small-diameter instruments, like catheters, bone drills, and steerable needles. For such applications, rotational scanning is usually most feasible and/or desired, making coupling of the light from the stationary OCT light source into a rotating part a common design issue. Coupling light between rotating optical parts is especially challenging due to the very strict demands on tolerances and alignments. We developed two optical couplings for high-speed (2000 rpm) rotational OCT that are applicable in instruments with diameters below 1 mm. The goal of the current research is to evaluate the designed optical couplings in terms of durability and feasibility. METHODS Two optical couplings (the “Steady Coupling” concept and the “Wagging Tail” concept) were built, and compared. The Steady Coupling concept consists of a stationary probe, tightly aligned with a rotating instrument tip, on a 0.2 mm thick bearing, with light being coupled between the stationary and the rotary part by two collimating GRIN lenses. The Wagging Tail concept is a design in which coupling is completely avoided and in which an optical fibre (with 0.25 mm GRIN lens at its tip) is deformed by the rotations of the instrument tip to make a conical scanning motion. Both concepts were tested on their weakest points. For the Steady Coupling concept, wear of the bearing was investigated. For the Wagging Tail concept, it was investigated whether the high-speed deformation cycles would create excessive heat or damage the optical fibre, which would cause deterioration of the light transmission. The wear of the bronze bearing and the damage to the optical fibre were tested simultaneously using a dedicated setup. RESULTS In the Wagging Tail concept the fibre still showed about 100 % efficiency after 350.000 rotations at 2000 rpm for a bending radius of 40 mm, a much sharper bend than in the prototype, and no noticeable heating or significant wear after rotating about 10 minutes. The bearing wear in the Steady Coupling concept was severe; after the tests, it appeared that the bearing had turned into powder and jammed the mechanism. CONCLUSION The simplicity, optical efficiency, and durability of the Wagging Tail concept clearly make this concept the optical coupling of choice for instruments where this mechanism can be applied. Drill tests on animal bone will have to shed light on the durability of the imaging lens in the tip of the drill. If the concept endures all tests, high-speed rotational OCT scanning can be embodied into many small diameter medical instruments. This research is supported by the Dutch Technology Foundation STW, which is part of the Netherlands Organisation for Scientific Research (NOW), and which is partly funded by the Ministry of Economic Affairs, Agriculture and Innovation. Project 7505