Improved double-integrating-spheres system for multiwavelength optical properties measurement: investigation and application

Abstract

Measurement of optical properties in near infrared is very important for the applications of diffuse optical tomography (DOT) and near infrared spectroscopy (NIRS), such as the in vivo detection of glucose concentration and oxygen saturation of tissue. In some wavelength, the optical properties of tissue are also applied in cancer diagnostics and therapy. Integrating sphere system is a widely adopted tool for in vitro measurement of tissue optical properties, but to our knowledge, most of the systems are only based on He-Ne laser or a spectrometer. A multi-wavelength optical property measurement system based on LDs in near infrared, double-integrating-spheres, and lock-in detection is introduced in this paper. Laser Diodes in 1300-1600nm are sinusoidal modulated in 30 KHz and an optical switch is adopted for wavelength selection. Studied on the theory of double integrated spheres, there are two main factors affecting the measurement accuracy: (1) light loss from the samples; (2) the inaccurate knowledge of the reflectance index of the under detecting sample. Based on the investigation of these factors and the results of Monte Carlo simulation, the system was carefully designed and fully improved. For evaluating the system, the optical properties of intralipid-10% solution and a mixture of intralipid /CuSO 4 solution were measured in 1310nm and compared with those reported in literatures or measured with other tools. From the results of the phantoms measurements, it is concluded that the system can get the reduced scattering coefficient and absorption coefficient with a relative error of less than 5% and 10%, respectively. Then the system is used to measure the optical properties of cervical tissues in vitro, for the wavelength between 600-1600nm.