改變輻射劑量及運用疊代式影像重組演算技術對於肺部低劑量電腦斷層影像品質影響之評估

Effect of Varying Radiation Dose and Using Iterative Reconstruction on the Image Quality of Low-dose Computed Tomography of the Lung

陳冠宇(Kuan-Yu Chen) ； 黃怡璇(Yi-Shuan Hwang) ； 陳緯遠(Wei-Yuan Chen) ； 林妤穎(Yu-Ying Lin)

《中華放射線技術學雜誌》 44卷4期 (2020/12) Pp. 210-219

摘要

本研究之目的為利用假體評估不同的輻射劑量及使用疊代式影像重組演算法對於肺部低劑量電腦斷層影像品質之影響，並提出最佳化的掃描參數組合。研究使用包含模擬結節之胸腔假體，利用128切之Hitachi SCENARIA電腦斷層掃描儀進行低劑量電腦斷層掃描。不同之輻射劑量為藉由改變管電壓100、120kV及管電流30、60、90、120 mA兩項參數。每張胸腔假體的影像皆使用肺部影像重組機制，並進行濾波反投影演算技術及四種不同設定之疊代式影像重組演算技術（C,E,Lv.3及Lv.5）進行影像重組。所得到的影像除進行品質因素及結節直徑分析之外，也會由資深放射師及物理師共三位，針對鮮銳度、影像雜訊及假影程度進行影像品質評分。結果顯示結節直徑之測量不會因為kV及影像重組演算法而有明顯之影響（p＞0.05）。此外，120 kV/90 mA/64 Lv.3掃描條件組合可提供最佳的影像品質及較佳品質因素，然而其CTDI_(vol)偏高（3.8mGy）。另一最佳化參數為120 kV/60mA/64 Lv.3可提供不錯的品質因素，且影像品質相較目前臨床設定為佳，但在1 cm葉狀型病灶的邊緣鮮銳度較低。結論為120kV/60mA為最佳化之肺部低劑量電腦斷層掃描參數，但建議在IR自動重組的設定額外增加64 Lv.3，以另外提供放射科醫師較低雜訊與假影之影像，同時使病人得到合理的輻射劑量。

關鍵字

低劑量電腦斷層 ； 胸腔假體 ； 疊代演算 ； 影像品質

並列摘要

This study was aimed to investigate the impact of the radiation dose and iterative reconstruction on the image quality of low-dose computed tomography (LDCT), and to provide the optimized scanning protocol based on the phantom study. A chest phantom contained various simulated nodules was scanned by LDCT protocol performed with a 128-section Hitachi SCENARIA CT scanner. Varied radiation dose was achieved by setting the tube voltage and tube current at 100, 120 kV and 30, 60, 90, 120 mA. Each image was reconstructed with the lung kernel, using filtered back projection (FBP) and iterative reconstruction (IR) with four different levels (settings of C, E, Lv.3, and Lv.5). Figure of merits (FOMs) and the diameters of the nodules were analyzed for each image. Additionally, image quality (IQ) score for each image was evaluated by one senior radiologic technologist and two medical physicists for sharpness, noise and artifact. The results indicated that diameter measurements were not significantly influenced by kV and IR setting (p＞0.05). Furthermore, 120 kV / 90 mA / 64 Lv.3 provided the best image quality score and better FOM. However, its CTDI_(vol) (3.8 mGy) is higher. Another optimized settings were 120kV / 60mA / 64 Lv.3, They both showed good FOM, and the image quality is better than the current clinical lung LDCT setting. However, the IQ score of sharpness for the 1 cm lobulated nodule is lower than the current clinical lung LDCT protocol. In conclusion, 120kV / 60mA could be the optimized LDCT protocol of the lung with an additional IR such as 64 Lv.3. This provide radiologists better image quality with less noise and artifact, and reasonable radiation dose for patients as well.

並列關鍵字

low-dose computed tomography (LDCT) ； chest phantom ； iterative reconstruction ； image quality