應用擴散光學方程式解析解於造影量測系統驗證之研究;Study on applying analytical solution of diffusion equation to the verification of diffuse optical imaging system

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題名:	應用擴散光學方程式解析解於造影量測系統驗證之研究;Study on applying analytical solution of diffusion equation to the verification of diffuse optical imaging system
作者:	梁雅婷;Liang, Ya-Ting
貢獻者:	光機電工程研究所
關鍵詞:	擴散光學斷層掃描;系統驗證;Diffuse Optical Tomography;System Validation
日期:	2017-04-24
上傳時間:	2017-05-05 17:16:32 (UTC+8)
出版者:	國立中央大學
摘要:	女性乳癌之發生率逐年增加，針對乳癌篩檢可藉由常規檢測機制診斷，可及早發現病灶並提早治療，以降低死亡率，本實驗室所發展近紅外光擴散光資訊斷層造影系統 (Near-Infrared Diffuse Optical Tomography, NIR-DOT)相對於常規之檢測方式，其優點為可排除輻射疑慮及顯示功能性影像。該造影系統利用近紅外光穿透組織後造成的光能量衰減及相位延遲資訊，藉由反算程式以重建組織內部之光學係數影像，依據正常組織與病灶組織在近紅外光波段下，其吸收係數及散射係數間的差異作為辨別之基準，用以協助乳癌檢測。然而在成像前，其實驗數據須利用均質標準塊進行校正，但在人體試驗中，實驗數據並無均質組織作為校正之基準，故其標準塊校正方式有所限制。本研究基於擴散方程式，由量測結果中光能量衰減及相位差變化之關係，推估組織的均質光學特性。此造影系統可分為光資訊掃描裝置及光學影像模擬，本研究主要針對光資訊掃描裝置進行校正及驗證，先針對所使用之元件進行特性探討，作為後續量測時校正的依據；以擴散光學方程式之結果作為驗證基準，在滿足理論假設之條件下，由光電量測模組進行光子密度波實驗，量測兩種已知光學係數之高散射介質，可獲得不同位置的光能量衰減及相位延遲，並與理論結果比較，得出實驗量測之結果與擴散方程式吻合，以確認光電量測模組之穩定性；除了上述之實驗架構，亦利用實驗室一進一出環形掃描裝置量測一有邊界之待測物，並以有限元素法模擬實驗量測條件之結果做為比較，結果顯示其兩者趨勢相符，用以驗證光學掃描裝置之可信度。由實驗中獲得不同位置對應於光能量衰減及相位延遲的斜率關係，將斜率帶入理論解析式中以推估光學係數，所得到之結果與待測物的光學係數接近，以確認光學掃描裝置之準確性。因此，透過實驗量測結果與理論解析式，可推估未知光學係數待測物之吸收係數與散射係數，而所推估之光學係數可作為影像重建流程中所需之初始值，以協助影像重建。;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.
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