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ANJALI.N.V
MEASUREMENT OF OPTICAL PROPERTIES OF HUMAN SKIN
ABSTRACT
In this, a very convenient approach has been made to determine the skin optical properties in-vivo using a simple optical fiber spectrophoto-meter. This method realises the determination of the optical properties of living tissue with the help of diffuse reflectance emitted from the skin when a mutiple wavelength light is incident on it. Oblique Incidence Diffuse Reflectance Spectrometry (OIDRS) is an optical method capable of quantifying both absorption coefficient and scattering coefficient of heterogenous media like skin with the help of the diffuse reflectance of the media. This will greatly assist in the diagnosis and even treatment of its pathologies. The dermatologist is able to identify the affected skin , by colour and other visual textural characteristics of the spectral images obtained fron the spectrophotometer.
INTRODUCTION
Skin cancers and tumors are an increasing problem around the world. Skin cancers account for about 40% of all the diagnosed cancers. Almost all skin cancers are curable, if detected early. Some cause morbidity if untreated. Currently, clinical dermatologists rely on visual inspection and experience to make an initial assessment of the skin lesion state. If further visual analysis does not provide a conclusive decision on the lesion state, such suspicious lesions are sent for biopsy analysis. Biopsy is unpleasant for the patient,slow in diagnostic results, and costly for the hospital on account of the wait time. Dermatologists would greatly benefit from a fast and noninvasive technique that could assist them in their clinical diagnostic decisions. Recent studies have suggested the close relationship between the various stages of skin diseases and the optical properties of the affected area. Finding the optical properties help a lot in the diagnosis. All the photo biological effects which are responsible for the variations in the optical properties of skin like the UV irradiation [which causes erythema (skin reddening), stimulates melanin synthesis, and even induce edema and tissue proliferation if the radiation dose is sufficiently large] need to be taken into consideration when prescribing phototherapy. So we need to find the optical properties of human skin.
OPTICAL PROPERTIES OF HUMAN SKIN
In terms of optical properties, biotissues (including blood, lymph, and other biological fluids) can be categorized into two large classes
strongly scattering (opaque) tissues such
as skin, brain, vascular walls, blood, and
weakly scattering (transparent) tissues such as the cornea and lens in the anterior eye chamber
Optical properties of human skin vary according to age and race. Biological tissues are optically inhomogeneous absorption media whose average refractive index is higher than that of air. This account for the partial reflection of radiation at the tissue/air interface (Fresnel reflection) while the remaining part penetrates the bio object. Multiple scattering and absorption are responsible for laser beam broadening and eventual decay as it travels through a biotissue whereas volume scattering is a major cause of the dispersion of a large fractionof radiation in the backward direction (backscattering).
Cellular organelles such as mitochondria are the main scatterers in various biotissues. Absorbed light is converted to heat and reradiated in the form of fluorescence; it is also consumed in photo-biochemical reactions. The absorption spectrum depends on the type of predominant absorption centers and water content of biotissues.