Biomedical applications of wireless continuous wave near infrared spectroscopy

Progress in research applications of near infrared spectroscopy (NIRS) and growing clinical interest have led to significant improvements in hardware and software. Amongst continuous wave systems the use of light emitting diodes, incorporation of spatially resolved optical geometry, algorithm refinement, development of portable systems, and wireless telemetry led first to portable NIRS instruments, then wearable systems, and now miniaturized self-contained devices. Measurement of absolute tissue oxygen saturation in both muscle and brain, and mapping of event related cortical hemodynamic responses using functional NIRS (fNIRS) have added specific measurement modalities. Wireless wearable systems and self-contained devices capable of measuring such modalities in addition to providing conventional monitoring of trends in oxygenated and deoxygenated haemoglobin concentration from baseline have increased the scope of research, expanded the population readily monitored, and opened new clinical avenues for applications involving NIRS. This review explores the range of biomedical applications reported using wireless continuous wave (CW) NIRS and fNIRS systems, summarizes key elements in the specification of available devices, and outlines potential future directions for clinical use of wireless NIRS technologies.