正子斷層造影是一種非侵襲性的核子醫學造影技術，可在受測者清醒的情況下測量其體內器官功能，已被廣泛運用於癌細胞之早期診斷。三維造影技術去除了偵檢器環之間的金屬隔板，大幅提高正子斷層造影的靈敏度，然而散射光子被偵測到的機率也隨之增加。散射事件會造成影像對比度下降，及量化分析的準確度降低，雖然目前已有許多修正散射事件的研究，但仍然沒有一種快速簡便且適用於臨床各種複雜情況的散射修正法。
本篇論文提出一種全新的射束擋塊散射修正法，即在受測物體周圍擺放高原子序物質所製成的射束擋塊，它對主射束會造成一定比例的衰減，對散射光子的影響則非常微小，因此散射事件量可從被阻擋的反應線中求得，再利用cubic-spline法內插得到整張正弦圖中散射事件的分布情形。
由實際測量一均勻水假體，以及蒙地卡羅模擬EEC腹部假體和Zubal胸腔假體，來驗證射束擋塊散射修正法的修正效果。結果顯示射束擋塊散射修正法能有效提高影像對比度、量化準確度，且不會造成雜訊增加，即使在受測物密度不均或體積較大的情況下，也能提供良好的修正效果。此外射束擋塊散射修正法更能同時修正多種情形的散射事件，如單次康普吞散射光子、多次散射光子和軸向照野外的散射光子，是一種操作簡便、運算時間短、修正效果佳的散射修正法。

Positron Emission Tomography (PET) is a non-invasive radiographic technique in the nuclear medicine, which can measure the organ function, and it has also been widely used for the detection of cancer cell. 3D acquisition mode removes the intra-plane septa. It increases the sensitivity of PET, however the scatter photons also increase hugely, that will blur the image contrast and decrease the quantification accuracy. There are many researches about scatter correction, but none of them is suitable for the complex clinic use.
In this thesis we bring up a whole new scatter correction method. Beam stopper is made of high atomic number material and it will attenuate the primary beam while has almost no influence on scattered photons. By using a beam stopper device, we can compute the quantity of scatter photons from the blocked line-of-responses (LOR). With these scatter sample points, we can interpolate the total scatter distribution in a sinogram by the cubic-spline interpolation method.
The performance was evaluated by experiment on a uniform water phantom and Monte Carlo simulation on EEC abdomen phantom and Zubal chest phantom. The results indicate the beam stopper method can improve the image contrast and the quantification accuracy obviously while no extra noise is induced even when the object is large or non-uniform. Besides, beam stopper method can deal with many kinds of scatter photons, such as single Compton scatter photons, multiple scatter photons and those originating from scanner out of field of view (OFOV). In sum, beam stopper method is a convenience, quick and effective scatter correction method for 3D PET.

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