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電腦斷層掃描應用於凝膠劑量計之掃描參數設定探討

THE EVALUATION OF THE COMPUTED TOMOGRAPHY SCANNING PARAMETERS SETTING USED IN THE GEL DOSIMETER

摘要


目的:近年來電腦斷層掃描儀被廣泛的應用在凝膠劑量計的影像資訊計讀。然而電腦斷層掃描參數的設定會影響到影像中雜訊,進而影響到劑量解析度,因此本研究目的是評估電腦斷層掃描儀作為 NIPAM 凝膠劑量計計讀工具時其最適化的掃描參數,以降低凝膠影像雜訊,提高訊雜比,增加凝膠劑量計臨床上之實用性。材料與方法:凝膠劑量計的影像擷取是利用電腦斷層掃描儀,並利用不同的掃描參數來對凝膠作影像擷取,而掃描參數是彼此獨立的變化,以去評估每個獨立參數對於影像雜訊的影響。結果:當管電流增加時,影像雜訊也隨之下降,當管電壓在 80 kVp 、120 kVp 、140 kVp 情形下,而管電流由 100 mA 提升至 230 mA 時,其影像雜訊分別可降低 59.3% 、64.1% 及 60.7%。同樣之情形,較高的管電壓可獲得較小的影像雜訊。而切面厚度 5 mm 下,管電壓從 80 kVp 提高到 140kVp 時,雜訊可降低 52.4%;而切面厚度為 10 mm 時,則可降低 55.0%。結論:利用電腦斷層掃描儀作為凝膠劑量計之資訊計讀時,掃描參數的設定需在管球熱負荷及影像雜訊之降低間作一平衡及最適化之考量。本研究所建議最適化之設定為管電壓 120 kVp 、管電流 200 mA,而切面厚度的選擇則依不同狀況來選定。最適化掃描參數的設定可以降低影像雜訊對於凝膠劑量解析度上的干擾,以增加凝膠劑量計臨床劑量評估上的正確性。

並列摘要


Purpose : In recent years, computed tomography scanners are widely used in the gel dosimeter for reading of the image information. However, the scanning parameter settings of computed tomography scanners will affect the image noise, thereby affecting the dose resolution. Therefore the aim of this study is to evaluate the optimal scanning parameters of the CT scanner as the reading tool applied in NIPAM gel dosimeter to reduce the gel image noise, improve signal to noise ratio and increase availability of gel dosimeter in the clinical. Materials and Methods : Computer tomography scanner was applied to capture image in the gel dosimeter. Different scanning parameters were used to capture gel images. Scanning parameters changed independently from each other in order to evaluate the image noise affected by each individual parameter. Result : When the tube current was increased, the image noise would reduce. If the tube voltage was 80 kVp, 120 kVp, 140 kVp, and tube current increased from 100 mA to 230 mA, it can reduce the image noise to 59.3%, 64.1% and 60.7 %, respectively. In the same case, smaller image noise was obtained in the higher tube voltage. If the tube voltage was increased from 80 kVp to 140 kVp with 5 mm slice thickness, the noise can be reduced 52.4%. When the slice thickness was changed to 10 mm, the noise can be reduced 55.0%. Conclusion and Discussion : While the computer tomography scanner was used in the gel dosimeter for reading of the image information, the scanning parameters settings were needed to compromise for balancing and optimizing between tube head loading and the decreasing of the image noise. The tube voltage of 120 kVp and tube current of 200 mA are recommended for the optimizing settings by this study but the slice thickness is selected according to different conditions. Optimizing scanning parameter settings can reduce image noise affecting the interference resolution of the gel dosimeter in order to increase the accuracy of gel dosimeter in the clinical dose assessment.

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