Basic Principle and Practical Implementation of Near-Infrared Spectroscopy (NIRS)

Various brain-imaging techniques, such as CT, fMRI, and EEG, have been introduced with their own strength and weakness. While CT and fMRI systems are anything but portable and thus undermine their use in dynamic conditions, EEG system has poor resolution. NIRS system, however, can be made portable with sufficiently high resolution, enabling its use in dynamic conditions and detecting valuable hemodynamics therefrom. This chapter provides a brief overview of the basic principle on NIRS, the imaging technique of diffuse optical tomography, and the superficial noise reduction method. Then, three different modulations methods for realizing the multi-channel CW NIRS are introduced. Lastly, the implementation of spread-spectrum-code-based CW NIRS is laid out for illustration.