Prospects for Development of Noninvasive Spectrophotometric Medical Diagnosis

Analysis of the development of modern medical diagnosis and treatment shows that there is a worldwide trend toward introduction into medical practice of sophisticated scientifically substantiated methods minimizing invasiveness, radiation load, and other physiologically and psychologically undesirable effects. Modern electronic, laser, and computer technologies, etc. are used to increase the efficiency of diagnosis and treatment. Population growth and rising incidence of many diseases increase the load on medical personnel, making it necessary to develop highly efficacious medical technologies providing minimal time per examination. These requirements are fully met by noninvasive (in vivo) laser and other optical methods of diagnosis, which have been extensively used in many industrially developed countries for the last 10-15 years [8, 11, 13]. These methods are based on the use of low-intensity (up to 10 mW) optical radiation for examination of organs and tissues. The light reflected by or transmitted through the tissues provides diagnostic information about their state. Processes of linear and quasi-linear interaction of light with optically inhomogeneous and semitransparent media (lymph, soft tissues, etc.) form the physical basis of these diagnostic methods [21]. For example, a light beam falling on skin is partially reflected by it and partially transmitted, reaching the connective and muscular tissues, vascular bed, etc. The transmitted radiation is multiply reflected (scattered) within biological tissues on the boundaries of inhomogeneous anatomical and cellular structures and partially absorbed by different substances (water, melanin, hemoglobin, etc.). A part of the radiation attenuated by absorption and multiple scattering emerges back from the skin surface [13], forming so-called back-scattered radiation flux Fbs. A small part of radiation is transmitted through the organ under examination. It forms the transmitted radiation flux Fτ. These fluxes can be detected using a photodetector. Different spectral components of optical radiation are absorbed and scattered by different biological tissues and substances. Thus, exposure of various organs and areas of human body to radiation of given intensity and spectral composition with further analysis of the intensities of spectral components of the fluxes Fbs and/or Fτ provide valuable information about the internal structure of the organ under examination. The principles outlined above are already implemented in such noninvasive optical diagnostic methods as laser Doppler flowmetry [5, 16], biophotometry [4], optical pulsoximetry [2], fluorescence diagnosis [3, 10, 12], etc. Methods of light scattering and absorption spectroscopy of biological tissues have been described in international literature [14, 15]. These methods are used to obtain information about the content of various natural pigments (melanin, oxyand deoxyhemoglobin, bilirubin, etc.) in tissues. The diagnostic methods listed above are implemented using similar measuring techniques and equipment (Fig. 1). Measurements are performed in transmitted (Fig. 1a) or reflected (Fig. 1b) light depending on the accessibility of the organ under examination. A single monochromatic radiation source 1 (laser) or a set of sources with different radiation spectra (including white light sources) can be used. Radiation is transmitted to the organ 2 under examination using an optical fiber 3. A receiving optical fiber bundle 4 transmits the detected fluxes Fbs and Fτ to a detection/spectral analysis unit 5. This unit can be implemented as a polychromator with a matrix photodetector, as individual optical filters and photodetectors, or even as a single photodetector used to measure the total radiation. Then, the electrical signal undergoes analog processing (amplification, filtration, etc.) in an electronic unit 6, is digitized, and is transmitted to a computer 7 for further processing. In some cases 1