| dc.description.abstract | According to the report from Health Promotion Administration (HPA), the incidence rate and mortality rate of women breast cancer increase gradually within a decade in Taiwan. Comparative to the common breast cancer detection method, such as X-ray mammography, near-infrared diffuse optical tomography (NIR-DOT) provides functional images and reduce the concerns of radiation. Due to different characteristics of optical properties, tumor tissue can be distinguished from normal tissue. NIR DOT uses near-infrared light to image tissue and measures the transmitted light from the tissue surface. Using the reconstruction algorithm with the measured data can estimate the optical coefficients (absorption coefficients and scattering coefficients) of the tissue. A standard homogenous phantom with optical properties similar to the object being imaging is used as the reference to calibrate the measured data before the reconstruction. In clinical trials, however, it doesn’t have this phantom for calibration. Therefore, bases on diffusion equation, this study will estimate the homogenous/bulk optical coefficients of the tissue by using measured data of the attenuation of the light intensity and the delay of the phase for facilitating calibration.
For the verification of the measurement system, we have to confirm the characteristic of the components used in NIR-DOT imaging system. From the characteristics of these components, optimal configuration can be set during the experiment. We use two different phantoms with known optical coefficients for verification of NIR-DOT imaging system under two measurement conditions. In the measurement condition of using uniform and infinite medium (without effect of boundary condition), the light intensity attenuates and the phase delays with increasing the distance between the source and the detector. The result of the experiment and the computed data from the derived analytical expressions based on the diffusion equation are close and show that the measurement system is stable. In the measurement condition of using circular phantom (with effect of boundary condition), the trend of result from NIR-DOT imaging system is also similar to the simulated data from solving the diffusion equation with the finite element method. With the previous results, it verifies the validity of measurement system.
According to the experimental data, the slopes of attenuation of light intensity and increase of phase delay with source-detector separation distance can be obtained. These slopes can further be used to estimate the optical coefficients based on the derived analytical expressions. Since the validity of our imaging system had been verified through the measurement of phantom with known optical properties, the homogeneous/bulk optical coefficients of tissue can be estimated from measured data, and be used as the initial value for reconstruction. | en_US |