Time-resolved near-infrared spectroscopic imaging systems

Time-resolved near-infrared light measurements have been used for about two decades to non-invasively provide functional images of the brain. After its first introduction in the late 1970´s, near-infrared spectroscopy, and subsequently, time-resolved near-infrared imaging, in parallel with photon propagation in living tissues, have been increasingly studied for various medical applications. In addition, there has been continuous research and technology development of more improved light transport models in tissues, practical simplifying assumptions to aid in analysis, more efficient imaging algorithms, and more reliable instrumentation. In this paper, we review time-resolved near-infrared spectroscopy and imaging from an engineering perspective and describe some of the key results of progress in the field. We discuss various techniques and hardware components of near-infrared spectroscopy and imaging systems, highlighting their advantages and limitations.