A calibrated 3D dual-barrel otoendoscope based on fringe-projection profilometry

Abstract

An otoendoscopic structured-light system based on fringe-projection profilometry is presented. Two standard rigid otoendoscopes are mounted onto each other and combined with a digital light projector and high-speed camera with respective frame rates of 120 and 210 Hz. Four phase-shifted sinusoidal fringe patterns are projected onto the object’s surface through the imaging channel of one endoscope with a 0° viewing angle, and the fringe patterns reflected by the object are recorded by the camera via the imaging channel of the other endoscope with a 30° viewing angle, resulting in a 3D shape measurement speed of 30 Hz in the current setup. Due to the angle between the projection and imaging axis, the projected patterns appear deformed by the object’s shape to the camera, enabling the reconstruction of its full-field surface height map. Geometric lens distortions in the optics of the projection and imaging channels were calibrated, resulting in a depth measurement precision between 10 and 30 µm and a lateral resolution of 10 to 25 µm. Otoendoscopic profilometry adds an extra dimension of depth to the standard 2D otoendoscopic image and can be used as a noninvasive technique to expand the qualitative depth perception of the physician with quantitative 3D data of the tympanic-membrane surface. Hence, the system holds the potential to provide objective diagnosis of tympanic-membrane and middle-ear disease. In future, the system will be optimized to allow real-time surface-shape visualization and handheld operation for use in a clinical setting.