Investigations On The Improvement Of Double-Integrating-Spheres System For Measuring Tissue Optical Properties

The double-integrating sphere (DIS) system is widely adapted in the measurements of tissue optical properties. The reflectance, transmittance and the collimate transmittance of the sample are measured by DIS system. Then the optical properties of the sample are reconstructed by inverse methods.In this paper, the double-integrating-spheres system is built based on the theory of the integrating sphere. The effects of light loss and'cross talk'between two spheres are investigated. To meet the need of the non-invasive blood glucose detection, the properties of different phantoms were measured and the measurement accuracy of the system was verified.First of all, the optical properties, which are used to describe the optical characteristics of the tissue, are introduced in this paper. Different measuring methods are also introduced and compared.Secondly, based on the developed DIS system, the factors impacting the measurement accuracy are analyzed. It has been found that the limitation of the diameter of the sample port can bring certain light loss, and the'cross talk'between the two integrating spheres also product some measurement error. Then Monte Carlo simulation was adapted to investigate the effects of light loss, crosstalk on the measurements of optical properties. To eliminate the effect of these factors on the measurement accuracy, the reflectance, transmittance and collimate transmittance measurement were calibrated.At last, the measuring accuracy, the repeatability and the measurement robustness of the DIS were verified using phantoms at 632.8nm. The liquid phantoms which employ the intralipid-20% as the scattering component and India Ink as the absorbing component were adapted in verification. Results show that the measurement repeatability is within 2%. The measurement error of the scattering coefficient and absorption coefficient are less than10% and 8%, respectively.In view of the application in the non-invasive blood glucose measurement of the optical properties of human skin, liquid phantoms were made, and measured using the DIS system. The results show that the system can be applied in the measurement ofthe human skin.