利用射束阻擋法修正三維正子造影之非真實事件貢獻

Correction of Non-True Coincidence in 3D PET using Beam Stopper Device

郭瓊蓮(Cyong-Lian Guo)

指導教授 ： 莊克士

國立清華大學/原子科學院/生醫工程與環境科學系/碩士(2008年)

https://doi.org/10.6843/NTHU.2008.00193

摘要

正子斷層造影掃描是在核子醫學上一項非侵襲性的檢查技術，提供臨床上功能性生理資訊。目前常用三維擷取模式來提高造影的靈敏度，但隨機與散射同符事件因此提高。一般隨機事件修正是利用即時的延遲時間窗修正法；散射事件修正是利用單次散射光子模擬法，然而以上修正法皆有缺失影響修正後的準確性。為有效矯正正子造影非真實事件，在此提出利用蒙地卡羅模擬旋繞式射束阻擋裝置修正法。
本研究使用GATE蒙地卡羅軟體模擬microPET R4系統以及射束阻擋修正法。利用射束阻擋裝置在不同角度下兩組正旋圖受檔塊遮蔽下的資訊，交叉計算出其非真實事件的貢獻量，因非真實事件分布是緩慢變化函數，所以可根據擋塊遮蔽部份的取樣點利用cubic-spline內插法得到整張正弦圖中非真實事件分布情形，再進行矯正。
本實驗研究優點在提出能窗範圍較大靈敏度提升的同時，掃描時間保持固定，射束修正法矯正的非真實事件分率31.55%與蒙地卡羅非真實事件分率29.62%的結果相近。旋繞式射束阻擋法是個方便、有效的修正方式，相信本研究所提出的矯正法是更適合於正子斷層造影臨床上應用。

關鍵字

旋繞式射束阻擋修正法 ； 散射事件 ； 隨機事件

並列摘要

Position Emission Tomography (PET) is a non-invasive technique in nuclear medicine, which can provide physiological information using molecular tracers. As the 3D acquisition of PET data increases, random and scatter coincidence events are increasingly relevant issue. They cause a uniform distribution of background on the image and degrade the accuracy of quantitative analysis. The conventional correction method for random and scatter events are achieved by the delayed time window method and Single Scatter Simulation(SSS) method. However, they increase noise and decrease image accuracy.
Beam stopper rotation method examines the feasibility of using beam stoppers (BS) for correcting non-true coincidence. The BS placed on the line of response (LOR) at two different locations rotated constant degrees, which absorbs a particular fraction of the true events. The non-true component, which can’t be stop at the LOR blocked by each stopper can be estimated. Assuming that the non-true radiation has a spatially slow-varying distribution, the whole non-true sinogram can be recovered using cublic-spline interpolation from these local measurements. BSR method reduces the effective sampling distance without increasing the stopper’s number. The study uses Monte Carlo (MC) simulation tools of 3-D PET, ”GATE” on a cold phantom to conduct the BSR method.
The main advantage of this study is achieved well corrected effect at larger energy window. The non-true fraction of BSR method is 31.55% and is close to the result of Monte-Carlo simulation. In sum, BSR method is a convenience and effective non-true correction method for 3D PET.

並列關鍵字

beam stopper ； scatter event ； random event

參考文獻

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