Optical Sensors in Medical Care

Abstract

Optical assessment of physiological parameters constitutes a group of measurement principles, which are very attractive because they often provide simple, non-invasive, continuous physiological monitoring conditions. Optical principles have been used in medical diagnosis since the dawn of the medical sciences. Well-known examples are the typical pallor of an anaemic patient or the yellowish skin of a baby with jaundice. Skin colours, and changes in skin colours, are typical for a number of infectious diseases. The interest for diagnosis, based on optical principles, has increased in recent years, partly because of the availability of new instruments and methods utilizing new optical technology. For a long time optical instruments have been used for analysis of samples taken from the patient in the laboratory. In these types of instruments, an optical beam typically passes a cuvette containing the sample and properties of the sample can be extracted by analysing absorption or scattering of light from the sample. A newer trend is that data are collected directly from a patient, thereby eliminating the need of sample collection. This paper discusses the principles of three such optical diagnostic measurements: Near infrared spectroscopy, pulse oximetry, laser Doppler flowmetry/imaging. These three methods have been chosen as examples of bio-optical progress and because they represent technologies at various stages of introduction into use in health care.