| Summary: | 碩士 === 國立中央大學 === 機械工程學系 === 105 === In recent years, breast cancer has the highest incidence rate happens in Taiwanese female, so early detection and treatment become an important issue. In medical screening technology, NIR DOT is a functional medical detection device, which is mainly based on the near infrared light source to penetrate the breast physiological tissue. Because the scattering coefficient of breast tissue is large regarding the near-infrared light band, the weak optical signal is received using high sensitivity detector after the light passes through the tissue and the variation of the tissue can be reconstructed using the diffusion equation. However, due to the long time work, the optical detection equipment will cause the characteristics of variation and the biases of the measurement results. Thus, it is necessary to measure the characteristics of the photo-detectors. The main propose of this study is to calibrate the characteristics of the photo-detector, design the simple and detachable near-infrared light source modules and use the high sensitivity photomultiplier tube (PMT) to measure. Using the dark space mechanism and automatic control with motor to design the correction device not only can inhibit the ambient light interference to the PMT but also can measure the characterization fast and accurately. According to the characteristic curve obtained by the PMT measurement, to make the use of the effective measurement range in different PMT control voltage, the optical power range of each control voltage are induced to a set of PMT optical power index bar. Besides, under the frequency domain measurement system, the phase difference relationship of PMT under different control voltage can be obtained, which is applied to the phase compensation correction of frequency domain optical measurement technology.
In this study, the phantom with 60 mm diameter which is trying to imitate the optical coefficient from human breast will be measured by three PMTs at the same time in the ring-diffused shaped optical tomography system, then the measured electrical signal will be taken into photoelectric conversion equation for the verification of characterization. Based on the photoelectric correction module designed in this study, the signal acquisition platform and calibration program of the photo-detector are established, which can obtain the characteristic curve of the photomultiplier tube accurately and quickly. Furthermore, the method is applied to the bed-type diffuse optical tomography system to improve the accuracy of the system measurement results.
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