Design Of An Experimental Prototype For Measuring Penetration Depth Of Near-infrared Light In Biology Tissue Phantom

Near Infrared Spectroscopy (NIRS), with its fast development in the recent years, is considered one of noninvasive optical measurements which are already widely used in the field of biomedicine. Since NIRS imaging system takes the advantage of small volume, light weight, low loss as well as cheap price, it makes significant effort to the study of tissue optics.On the basis of optical diffusion theory and other related concepts, as well as reference to the rationale of near-infrared brain function image system, a set of three continued wavelengths near-infrared sample measurement machine for penetration depth and one device in control of the separation of light source and detector. This system draws in three-row integrated LED (the center wavelengths are at 735 nm, 805 nm and 850 nm) as light source, by using NI data acquiring board to provide the clock circuit so as to control the light source drive chips. When near infrared lights penetrate biology tissue phantom, this data acquiring board transports the intensity of light received by the detector to the PC for analysis. The system sampling resolution can reach to 400 HZ and the detected dimensional resolution is 1.0 mm, which is suitable for the measurement of the penetration depth experiment.Then, a series of performance tests are taken in order to valuate the performance of this system, as a result, the average voltage of noise is between 2.34 mV-2.35 mV; the fluctuation of signal voltage is less than 1.5 % when the system work for 30 minutes; the average power of the light source which is under the regulation of the laser radiation standard; and the error of the device in control of the separation of light source and detector is 0.01 cm which is satisfied to the needs in the experiment.The final penetration depth experiment result illustrate that the location at which NIRS penetrate deepest in liquid tissue phantom is in the middle of light source and detector. The change of maximum penetration of NIRS at 735 nm, 805 nm and 850 nm first increase then decrease with increasing separation of light source and detector in the homogeneous phantom with Reduced Scattering Coefficient is 15.0 cm-1 and Absorption Coefficient is 0.1 cm-1, and the value are 16.4 mm,19.2 mm和21.6 mm. Moreover, the Tissue optical properties of the phantom are changed. When reaching to the maximum penetration depth, attenuation of the light source gained from the detector is similar with the result emulated in the computer. Therefore,those above prove that the system is feasible to NIRS penetration depth in biology tissue phantom.