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Infrared Hollow Optical Fiber Probe for Localized Carbon Dioxide Measurement in Respiratory Tracts
Takashi Katagiri1, Kyosuke Shibayama2, Takeru Iida3
1Graduate School of Engineering, Tohoku University, 6-6-05 Aoba, Sendai 980-8579, Japan. katagiri@ecei.tohoku.ac.jp.
Abstract:
A real-time gas monitoring system based on optical absorption spectroscopy is proposed for localized carbon dioxide (CO₂) measurement in respiratory tracts. In this system, a small gas cell is attached to the end of a hollow optical fiber that delivers mid-infrared light with small transmission loss. The diameters of the fiber and the gas cell are smaller than 1.2 mm so that the probe can be inserted into a working channel of common bronchoscopes. The dimensions of the gas cell are designed based on absorption spectra of CO₂ standard gases in the 4.2 μm wavelength region, which are measured using a Fourier-transform infrared spectrometer. A miniature gas cell that is comprised of a stainless-steel tube with slots for gas inlet and a micro-mirror is fabricated. A compact probing system with a quantum cascade laser (QCL) light source is built using a gas cell with a hollow optical fiber for monitoring CO₂ concentration. Experimental results using human breaths show the feasibility of the system for in-situ measurement of localized CO₂ concentration in human airways.
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