Miniature, minimally invasive, tunable endoscope for investigation of the middle ear

Abstract

We demonstrate a miniature, tunable, minimally invasive endoscope for diagnosis of the auditory system. The probe is designed to sharply image anatomical details of the middle ear without the need for physically adjusting the position of the distal end of the endoscope. This is achieved through the addition of an electrowetted, tunable, electronically-controlled lens to the optical train. Morphological imaging is enabled by scanning light emanating from an optical coherence tomography system. System performance was demonstrated by imaging part of the ossicular chain and wall of the middle ear cavity of a normal mouse. During the experiment, we electronically moved the plane of best focus from the incudo-stapedial joint to the stapedial artery. Repositioning the object plane allowed us to image anatomical details of the middle ear beyond the depth of field of a static optical system. We also demonstrated for the first time to our best knowledge, that an optical system with an electrowetted, tunable lens may be successfully employed to measure sound-induced vibrations within the auditory system by measuring the vibratory amplitude of the tympanic membrane in a normal mouse in response to pure tone stimuli.

Keywords: (110.4500) Optical coherence tomography; (120.7280) Vibration analysis; (170.0170) Medical optics and biotechnology; (170.2150) Endoscopic imaging; (170.4580) Optical diagnostics for medicine; (170.4940) Otolaryngology; (220.0220) Optical design and fabrication.

Fig. 1

Tunable miniature endoscope: isometric projection of a three-dimensional CAD model (a), components of the endoscope photographed before assembly (b), optical schematic of the tunable endoscope (c), photograph of the prototype with ruler in the foreground for scaling purposes (c).

Fig. 2

Pseudo 3D opto-mechanical schematic of a system used to test optical performance of the miniature tunable endoscope.

Fig. 3

Images of 1951 USAF resolution target acquired using experimental system schematically depicted in Fig. 2. From the top left, images are recoded at: 0 mm (a), 0.3 mm b) 0.8 mm (c) and 2.3 mm (d) endoscope working distance, measured between distal end of the GRIN lens and front, chromium coated, surface of the 1951 USAF resolution target. During experiment images were recorded at arbitrary selected resolution of 1944x2592 (height to width ratio of 0.76) and their brightness was adjusted for visualization purposes.

Fig. 4

Schematic diagram of the experimental setup. SLED – super luminescent diode, PoC – polarization controller, PC – laptop PC, RM – reference mirror.

Fig. 5

Performance of the tunable needle like endoscope system in OCT set-up in function of probe working distance: resolution in lp/mm (a) and diameter of the field of view in mm (b).

Fig. 6

Phase of the OCT signal in function of frequency of the audio stimulus at 50 SPL, latex membrane (a) and ear drum of the normal mouse (b).

Fig. 7

2D isometric projection of OCT volumetric data onto xy plane with plane of the best focus at the incudo-stapedial joint (a) and at the stapedial artery (b). (c) and (d) B-scans through direction A-A from subplots (a) and (b) respectively. (e) and (f) B-scans through direction B-B from subplots (a) and (b) respectively. Please note that position of miniature tunable endoscope was fixed during this experiment.