Endoscopic Low Coherence Interferometry in Upper Airways Yves Delacrétaz a∗ , Daniel Boss a , Florian Lang b , and Christian Depeursinge a a Advanced Photonics Laboratory, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland. b Centre Hospitalier Universitaire Vaudois (CHUV), Service ORL, CH-1011 Lausanne Switzerland. ABSTRACT We introduce Endoscopic Low Coherence Interferometry to obtain topology of upper airways through commonly used rigid endoscopes. Quantitative dimensioning of upper airways pathologies is crucial to provide maximum health recovery chances, for example in order to choose the correct stent to treat endoluminal obstructing pathologies. Our device is fully compatible with procedures used in day-to-day examinations and can potentially be brought to bedside. Besides this, the approach described here can be almost straightforwardly adapted to other endoscopy-related field of interest, such as gastroscopy and arthroscopy. The principle of the method is first exposed, then filtering procedure used to extract the depth information is described. Finally, demonstration of the method ability to operate on biological samples is assessed through measurements on ex-vivo pork bronchi. Keywords: 120.3180 Interferometry, 170.2150 Endoscopic imaging, 110.1650 Coherence imaging 1. INTRODUCTION We have developed a way to measure lumen size and stenosis length during routine endoscopic examination, since this procedure has to be performed in all cases. Nowadays, direct measurements can be performed with rigid endoscopes, fibroscopes, and with specifically designed probes, as with the optical coherence tomography method, 1 and more recently, the Fourier domain optical coherence tomography. 2 In low-coherence interferometry, or coherence radar, 3 the envelope of the interference signal is detected, rather than the evaluation of the phase itself. This is usually achieved by calculating the correlation signal of several phase-stepped images, thus providing 3D contouring. 4 “Coherence gating” techniques have the advantage of providing absolute depth position information, in opposition to the phase difference signals used in holography or speckle interferometry, 5–7 that give only relative measurements. The counterpart is that gating techniques often require multiple acquisitions to demodulate the signal, preventing live recording, unless using rather complicated systems with either multiple sensors, or multiple images on the same detector, 8 and fine image registration techniques. We introduce endoscopic low coherence interferometry (ELCI), an innovative technique that can be used to retrieve keys dimensions in the human upper airways. A fibered interferometer using a low coherence laser diode has been built around a standard rigid endoscope. This device is fully compatible with procedures used in clinical day-to-day examinations and can potentially be brought to the bedside. Only one acquisition is needed to obtain an absolute contour depth, which allows to achieve contouring even in harsh environments. Further author information: (Send correspondence to Y. Delacrétaz) Y. Delacrétaz: E-mail: yves.delacretaz@epfl.ch C. Depeursinge: E-mail: christian.depeursinge@epfl.ch Optical Coherence Tomography and Coherence Techniques IV, edited by Peter E. Andersen, Brett E. Bouma, Proc. of SPIE-OSA Biomedical Optics, SPIE Vol. 7372, 73721Z © 2009 SPIE-OSA · CCC code: 1605-7422/09/$18 · doi: 10.1117/12.831801 SPIE-OSA/ Vol. 7372 73721Z-1