| BackgroundBecause of limited technique, the optical absorption properties of the skin tissue have not been deeply understood and investigated in recent years. The existing data about skin optical properties were obtained from in vitro skin samples or by mathematic simulating. Most of those are mainly about white or black race and seldom about yellow race. Because in vitro skin samples are utterly dissimilar with vivo tissue in blood supply, water content, protein activity and tissue structure. The optical properties in vitro tissue may differ from vivo tissue consequentially. So, its optical data can't provide useful instructions for clinical laser cosmetics. Clinical laser protocols are usually based on visual inspection results and clinical experience, and the optical properties of skin tissue, as far as they are known, are not useful to optimize these protocols. Therefore, it is greatly necessary to investigate the optical properties of pigment-diseased skin of yellow race in vivo. It will not only provide useful results for exact diagnosis and further detailed classification of the pigmented skin diseases and for selecting proper laser parameters, but will be helpful to improve the cure rate and to reduce the complications.ObjectiveThe aims of the study are to investigate the photon transmission and the chroma theory of pigmented-diseased skin, and to establish a platform for detecting the absorption spectra of skin tissue in vivo without damage. This platform can explore the light absorption effect of various pigment-diseased skin of yellow race, and investigate the changes of absorption spectra during clinical laser treatments. At the same time, a standard chroma detecting system is to be set up, with which the distribution of chroma value of various pigmented skin disease is analyzed.Methods and results1. The formula calculating the light absorption ratio of pigment-diseased skinThe melanin, haemoglobin and water are the chiefly chromophores in pigment-diseased skin tissue for all wavelengths between 400 and 1200nm. The energy of the incident light from the white light source was ultimately divided into three sorts: reflection, transmission and absorption. Based on the light propagation theory of Kubelka-Munk model, the reflection light ratio (Red) and transmission light ratio (Ted) can be deduced as follow:And the absorption light ratio can be calculated as:With the equation above, we can detect the absorption spectra of skin samples and plastic flaps but not that of the vivo skin tissue. The visible and near-infrared light of the spectra can penetrate into melanin only to the depth of 1/10 of that of the normal skin tissue, and its effective attenuating coefficient in melanin exceeds that of the normal skin tissue by 10 times. The light from 400nm to 1200nm, when penetrated into the pigment-diseased skin tissue which contains a great deal of melanin, will be completely absorbedfinally, which means the transmission ratio T( A ) equals to zero. Therefore A( A )=1-R(A )2. Two-level classificationThe absorption ratio of short wavelengths reflects the light absorption in superficial diseased tissue, whereas the absorption ratio of long wavelengths accounts for the light absorption in superficial and deep diseased tissue together. The density of pigmentary particle in superficial tissue can be known from the spectra of short wavelengths, and that in deep tissue can be educed by comprehensively analyzing the absorption ratio of long wavelengths and short wavelengths. By this way, the density of melanin in each stratum of the skin tissue can be known.3. Establishing the spectrum-detecting platformA platform for detecting the absorption spectra of human skin tissue in vivo was set up composed of a standard white light source, a spectrometer, a fiber-optic probe and virtual instrument system. Programs such as spectrum detecting program, spectrum connecting program, spectrum analysing program and spectra comparing program were designed with the virtual instr...
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