By Cnr Ifn
Optical radiation in the visible and near-infrared spectral region (600-1100 mm, NIR) can be use to probe non-invasively biological tissues because: - biological tissues are relative transparent in this spectral range (named "therapeutic window") allowing the optical radiation to penetrate for a few centimeters and to have access also to deep structures (such as muscle or cerebral cortex) operating from the outside in a completely non-invasive way; - the propagation of light in diffusive media has the characteristics of a chaotic process (named "photon migration"), mainly ruled by the absorption and diffusion phenomena, and can be described by suitable mathematical models that allows to retrieve the optical properties, i.e. the absorption and reduced scattering coefficient, of the probed tissues; - the absorption spectra of the chromophores present in biological tissues (such as oxygenated and deoxygenated hemoglobin, lipid, water, collagen, etc., in case of human tissues, or chlorophyll, carotenoids, anthocyanins, water, etc. in case of vegetables) exhibit different characteristics that a multispectral approach can exploit to determine their concentrations; - The scattering spectra are related to the microstructures of the probed tissue and give access in particular to the density and dimensions of the scattering centers. Different approaches to NIRS are possible, i.e. continuous wave, frequency-domain, and time-domain. We adopted the time-domain approach, that has the advantage of increasing the spatial resolution in depth, and of a better decoupling of absorption and scattering phenomena, allowing an accurate estimation of tissue optical properties. In this framework, we are working to two main applications. Monitoring of the hemodynamics and oxidative metabolism Portable and compact instruments for TD-NIRS are developed in our laboratories with the aim of non-invasively monitoring the concentration of oxy- and deoxy hemoglobin in the tissues (skeletal muscle, brain cortex). These instruments have been successfully applied to both adults and children, during measurement protocols involving external stimuli, or as continuous monitor also at the bedside. More recently TD-fNIRS instrumentation has been integrated with a new developed instrument based on the Diffusion Correlation Spectroscopy (DCS). This technique relies on the light intensity decorrelation determined by red blood cells movement in the tissue, allowing to have an estimation of the bool flow. The combination of the hemoglobin concentrations and blood flow allows to give an estimation of the metabolic rate of oxygen consumption. Non-destructive assessment of fruit quality A TD-NIRS instrument, working at 14 wavelengths in the spectral range 540-1064 nm, has been successfully used in various measurement campaigns, both directly in the field and in the laboratory. The main problems addressed have been: the post-harvest management of different types of fruit, such as apples, pears, peaches, nectarines, kiwis, plums and mangoes; the non-destructive detection of defects in fruit; the prediction of the quality of transformed products.
