Abstract
Near-infrared spectroscopy has proven to be a valuable method to monitor tissue oxygenation and haemodynamics non-invasively and in real-time. Quantification of such parameters requires measurements of the time-of-flight of light through tissue, typically achieved using picosecond pulsed lasers, with their associated cost, complexity, and size. In this work, we present an alternative approach that employs spread-spectrum excitation to enable the development of a small, low-cost, dual-wavelength system using vertical-cavity surface-emitting lasers. Since the optimal wavelengths and drive parameters for optical spectroscopy are not served by commercially available modules as used in our previous single-wavelength demonstration platform, we detail the design of a custom instrument and demonstrate its performance in resolving haemodynamic changes in human subjects during apnoea and cognitive task experiments.
Highlights
Near-infrared spectroscopy (NIRS) is an optical technique that uses non-ionising electromagnetic radiation to extract meaningful information in a wide range of industrial and biomedical applications
The ability to evaluate concentration changes in oxygenated haemoglobin (HbO2), de-oxygenated haemoglobin (HHb), total haemoglobin and oxygen saturation (SO2) in tissues, combined with the non-invasive nature of this method, which allows for bedside monitoring, has established NIRS as a powerful clinical tool for brain, muscle or breast monitoring [3]
The combined diffused light is collected from the subject under test using a 50/125 μm fibre, which is connected to the input port of a custom wavelength division multiplexer (WDM) (WDM12P-111-680/850-50/125, OZoptics Ltd)
Summary
Near-infrared spectroscopy (NIRS) is an optical technique that uses non-ionising electromagnetic radiation to extract meaningful information in a wide range of industrial and biomedical applications. We use a maximum-length sequence (MLS) as our temporally broadened pulse, owing to its excellent autocorrelation properties This sequence is transmitted optically to the subjects under test, and the diffused light is collected based on standard time correlated single photon counting (TCSPC)-based detection techniques. In this work we demonstrate the design and implementation of a new system based upon the spread-spectrum technique, developing our own optical transceivers and optical components to enable dual-wavelength operation, optimised for use in NIRS applications. This enables us to demonstrate the measurement of functional responses during cognitive experiments. A detailed discussion of the potentials and future improvements of the proposed setup is offered
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