運用田口方法與自製肝臟假體評量電腦斷層掃描肝臟血管的最小可分辨差異

Quantifying the minimum detectable difference of computed tomography scanned images using Taguchi analysis: a feasibility study with an indigenous hepatic phantom and planar gauge

彭炳儒(BING-RU PENG)

指導教授 ： 潘榕光

中臺科技大學/健康科學院/醫學影像暨放射科學系暨研究所/博士(2020年)

摘要

於本研究，電腦斷層肝臟血管攝影的影像最小可偵測差異以及掃描參數最佳化設定分析，是使用自製的肝臟假體、線群塊規，以及田口方法進行。將電腦斷層的因子（參數）設定依照田口L18直交表的建議排列，於此所探討之因子為：管電壓峰值（kVp），管電流乘積(mAs)，掃描螺距(pitch)，照野尺寸(mm-FOV)，以及管球旋轉秒數(rotation time: Sec)，等五項。每項因子各有二或三個設定水準。18次掃描結果利用統計學以及交互作用的分析，相當於162次（2×3×3×3×3）實驗的分析數據。最佳化參數的設定結果為：A1 (120 kVp)、B3 (300 mAs)、C1 (0.641 pitch)、D2 (320 FOV-mm)、E3 (1.0 sec)。通過學生t-檢定於95%信心水準設定的影像最小可偵測差異為2.31mm深度為3.7mm。相較於直交表第七組設定(2.62mm，深度 3.9mm)以及習用參數設定(3.18mm，深度 4.2mm)，顯然最佳化參數可提供更佳的臨床掃描策略。本研究成功地以田口方法最佳化了電腦斷層的臨床掃描策略，並且藉由五組臨床實際驗證，證明最佳化設定較習用參數更可清楚呈現了患者肝臟內部的細微血管影像以及周圍病灶的輪廓。

關鍵字

CT影像 ； 線群塊規 ； 田口方法 ； 直交表 ； MATLAB ； 學生t-檢定

並列摘要

The minimum detectable difference (MDD) of computed tomography angiography (CTA) scanned images was quantified and optimized according to an indigenous hepatic phantom, line group gauge and Taguchi L18 optimization analysis in this work. Optimal combinations of CT scan factors in each group of level combination were determined using the Taguchi method, in which all factors were organized into only 18 groups, yielding analytical results with the same confidence as if each factor had been examined independently. The five considered operating factors of the CT scan were (1) kVp, (2) mAs, (3) pitch increment, (4) field of view (FOV) and (5) rotation time for one loop of CT scan. Each of these factors had 2 or 3 levels. Therefore, 162 (2×3×3×3×3=162) combinations were considered. The optimal setting was 120 kVp, 300 mAs, 0.641 pitch, 320 mm FOV and 1.0 sec of rotation time of CT scan. The minimal MDD was 2.38 mm under 0.37 mm of the slit depth from the revised student’s t-test with 95% confidence level. In contrast, the MDD of conventional and the best one (no. 7) among all original 18 groups is 3.15 mm under 0.42 mm slit depth and 2.62 mm under 0.39 mm slit depth, respectively. In this study, the clinical scanning strategy of CT examination was successfully optimized by applying Taguchi method. In addition, with verification on five sets of clinical images, it is indicated that subtle blood vessels and the contours of surrounding lesions inside patients’ livers were more clearly demonstrated with optimized scanning parameters, as compared to current settings.

並列關鍵字

CT scan imaging ； line group gauge ； Taguchi ； orthogonal array ； MATLAB ； student’s t-test

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