光聲造影跟現有的血氧飽和濃度量測技術相比有著高解析度、高天生對比度及非侵入性等優勢。本論文主要的工作是對光聲造影技術為基礎的血氧飽和濃度定量技術在使用活體應用中遇到的問題作探討與提出解決方法，並使用電腦模擬驗證所提出之演算法是否有改良傳統方法的問題並達到定量血氧飽和濃度量測的目的。在本論文中我們首先對於傳統基於最小平方法之反矩陣運算在活體應用中計算血氧濃度時所會遇到的問題作探討；因傳統的計算方法必須滿足訊號峰值和吸收係數成正比這項基本假設，才能定量的量測血氧濃度，但在活體應用中，目標血管上方通常會有其他組織影響雷射能量密度的分佈，使達到目標血管的能量密度會隨雷射光波長改變，影響訊號峰值和吸收係數的正比性造成估計濃度時的誤差；此外當目標血管的吸收係數隨著雷射光波長和血氧濃度改變時，此吸收係數的擾動也會影響上方組織的雷射能量密度分佈，進而影響傳統方法計算血氧濃度時的基本假設。在電腦模擬驗證中，我們利用蒙地卡羅模型來模擬組織和目標血管在雷射光照射後之能量密度分佈，並考慮了蒙地卡羅模擬在對於不同光子數量和不同的目標血管幾何結構等變因之穩定性，選擇適當的參數後模擬組織能量密度隨雷射光波長改變和吸收係數擾動兩種情況，再以傳統基於最小平方法之反矩陣運算估計目標血管的血氧濃度，估計結果驗證了若在基本假設中訊號峰值和吸收係數的正比性受到影響之情況下，直接使用基於最小平方法之反矩陣運算求得的血氧濃度和預設值會產生誤差，而透過我們所提出的針對能量密度變異之最佳化演算法，可有效算出一最佳化的能量密度補償係數矩陣，改良傳統之反矩陣運算在能量密度變異情況中估計之誤差，估計出的結果更接近預設值，也證明了此演算法有潛力幫助我們在活體應用中利用光聲造影達到定量血氧飽和濃度量測的目的。

Blood oxygenation measurement with photoacoustic techniques has the advantages of good ultrasonic resolution and high intrinsic optical absorption contrast and is non-invasive compared with other measurement techniques. The purpose of this study is to develop a photoacoustic-imaging-based quantitative measurement technique for the determination of blood oxygen saturation in-vivo application, and verify its feasibility by computer simulation to improve the problems of blood oxygen saturation estimated by traditional method. In this study, we first make discussions for problems of traditional least-squares-based matrix inverse method. The well quantitative measurement of blood oxygen saturation by the traditional method have to satisfy the basic assumption that the signal peak value is proportional to the absorption coefficient. However, in real situations, tissues above the target blood vessel will vary the laser fluence on the target vessel at different wavelengths. Thus, traditional “Least Squares” method can not offer good blood-oxygenation measurement. Furthermore, fluence above target vessel will be perturbed due to an absorption perturbation which also influences the basic assumption. In computer simulations, we used a Monte Carlo simulation of photon transport, and determined the appropriate number of photon packets and structure of target vessel to achieve stabilized SO2 measurement by used the energy deposition results at several wavelengths, and the measurement results showed that the blood oxygenation estimated by the traditional “Least Squares” method is lower than the default blood oxygenation values. To foster the practicability of this photoacoustic blood oxygenation measurement technique, here a “Fluence Compensation” algorithm is proposed to obtain fluence compensation coefficients with an optimization algorithm, which compensates the fluence changes depending on different wavelengths, and the proposed algorithm provides better estimation for blood oxygenation. It is demonstrated that our mathematical model has the potential to perform blood-oxygenation measurement for in vivo applications.

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