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.
Highlights
Imaging lung functions is essential for planning procedures in surgery and the treatment of pulmonary emphysema and atelectasis [1,2]
We propose a real-time CO2 monitoring system that is based on optical absorption spectroscopy
For localized CO2 measurement in respiratory tracts, we proposed a real-time gas monitoring system based on optical absorption spectroscopy
Summary
Imaging lung functions is essential for planning procedures in surgery and the treatment of pulmonary emphysema and atelectasis [1,2]. A computed tomography (CT) is the most commonly used method for functional lung imaging that provides three-dimensional high-resolution images [3]. Lung ventilation scintigraphy based on images of radioactive gases taken by a gamma camera is commonly used to visualize localized ventilation functions of lungs [4]. The use of radioactive materials and low image resolution are problematic with this method. Aside from these methods that provide information on tissue configuration and volume, direct measurement of localized gas concentration and airflow using a catheter provides more detailed information on localized lung functions [5,6,7,8].
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