Non-invasive optical oxymetry

Near Infrared Spectroscopy (NIRS) is a promising technique for the non-invasive determination of human tissues perfusion and oxygenation. Radiation from a light source between 700 and 900 nm is injected into the tissues and a photodetector collects its back-scattered portion. A measurement of absorption gives an estimate of the quantity of absorber in a volume between source and detector, in particular absorption due to haemoglobin is related to the degree of blood oxygenation. Because of the clinical relevance of a local oxygenation measurement, during last years commercial NIR oxymeters have been developed. All of them must be operated from fixed position and use expensive components like laser sources and/or extremely complex probes. The purpose of our studies was then the design of a family of oxymeters meeting the requirements of compactness, cost effectiveness, ease of use through a microcontroller-based technology on mixed analog-digital signal front-ends; moreover, the choice of commercial LED sources helps to achieve the results seen before. First instrument is a portable oxymeter, with an internal memory and battery powered, for measurements on great muscles during muscular activity; it has two LED sources at different wavelength and leaves the subject under test free to move. Another line of study is the development of a modular acquisition system in which each module has its own acquisition front-end. The operating parameters derived from this prototype can be employed in the design of a purpose-specific NIR oxymeter. One of the modules, based on a four sources-two photodiodes scheme, has been dedicated to cerebral oxymetry and it finds its applications in basic research, hemorrhages detection and during surgery, when a continuous and real-time measurement can help to avoid permanent damages to the tissues.