肺臟腫瘤於動態顯影CT影像之特徵分析

肺癌為國人重要癌症死因，因此如何診斷肺癌成為近代醫學重要的研究課題。肺部電腦斷層掃描（CT，Computed Tomography）為診斷肺臟腫瘤最重要之工具。過去文獻顯示良、惡性病灶之顯影特性有所不同並代表著腫瘤血管之特徵。本研究使用動態顯影之CT影像，探討肺部結節影像特徵參數不同病灶之特性。研究主要是對直徑小於3公分之單一肺部結節（Solitary Pulmonary Nodule）進行分析使用。共使用病案經證實之 82例（良性18例、惡性64例）動態顯影之CT影像；其顯影時間為顯影劑注射前（0秒）以及注射後25秒與50秒。利用影像處理之半自動分割技術，分別對包含腫瘤最大徑之單一切片與包含整體腫瘤之多張切片影像進行分割。使用紋理特徵含密度（Density）以及經由共相關矩陣（Co-correlation Matrix）所計算之熵（Entropy）、能量（Energy）、對比度（Contrast）和齊次性（Homogeneity），同時加上似圓性、面積/體積和直徑…等形態特徵進行參數分析。本研究使用之統計分析方法包含變異數分析以判斷顯影對於特徵參數之影響，t檢定分析以區別良、惡性腫瘤的差異，接收器操作特性曲線（Receiver Operating Characteristic）以曲線下面積（AUC，Area Under Curve）評估參數診斷效益；並利用倒傳遞類神經網路分析訓練組（良性11例、惡性39例）與測試組（良性7例、惡性25例）進行特徵參數之整合，以提升系統對良、惡性腫瘤的鑑別度。研究結果顯示二維紋理參數於腫瘤最大徑之單一切片的統計結果大致優於腫瘤整體之多張切片合併的統計結果。以腫瘤最大徑之單一切片分析顯示，在惡性腫瘤之紋理參數Density（P=0.015）、Entropy（P=0.011）和Energy（P=0.024）受到顯影的影響改變較為顯著。在良、惡腫瘤群組間差異分析，Contrast於顯影前最為顯著（P=0.001）； Density（P=0.009）、Entropy（P=0.002）、Energy（P＜0.001）和Homogeneity（P=0.001）在顯影劑注射後50秒最為顯著。在診斷效益上，Contrast於顯影前所得之診斷效益最大（AUC=0.714），參數Density（AUC=0.725）、Energy（AUC=0.762）、Entropy（AUC=0.738）和Homogeneity（AUC=0.741）於顯影劑注射後50秒所得之診斷效益最大。透過倒傳遞類神經網路整合上述具診斷效益之參數，以隨機選取分成訓練與測試群組，可得到鑑別良、惡性準確率為0.791±0.017、靈敏度為0.908±0.018及專一度為0.457±0.107。研究發現利用動態顯影之CT影像可偵測肺臟腫瘤於不同時間之顯影，因而改變其內在紋理特徵，使良、惡性肺臟病灶之區別更加明顯，同時提供紋理參數分析在影像臨床診斷之參考依據。未來可能使用多偵檢器電腦斷層掃描（MDCT，Multi-Detector Computed Tomography）儀進行體積掃描，以達縮短檢查時間以及提高影像解析度，幫助腫瘤血管新生特性之了解；若能配合電腦輔助診斷（Computer Aided Diagnosis）之技術處理其龐大的資料量，相信更可有效提升臨床診斷之效益。

關鍵字

紋理分析；顯影；肺臟腫瘤；電腦斷層掃描

並列摘要

Lung cancer is one of popular cancer for patient’s death in Taiwan. The diagnosis the lung cancer in early stage becomes very important research issue. Previous studies show that vascular enhancement character was different from the different kind of nodule in Computed tomography (CT) images. The purpose of this study is focused on feature analysis for early stage lung nodule in dynamic contrast enhancement CT image. In this study, dynamic contrast enhanced CT images for lung nodule size smaller than 3 cm were used for analysis. Totally, 82 cases which had final histopathologic diagnosis by CT-guided biopsy and subsequent surgical biopsy as 18 benign cases and 64 malignant cases were used. Three sets of dynamic enhanced CT images that are 0 (pre-contrast), 25 (post-contrast1), and 50 (post-contrast2) seconds delay after contrast injection were acquired. Nodules within single slice image of the largest diameter of nodule or within multi-slice image of whole nodule were segmented thru a semi-automatic method. The characters of textural such as: density, entropy, energy, contrast, and homogeneity, and morphological parameters such as: area/volume, diameter, and circularity were extracted for feature analysis. Following by one way analysis of variance, independent sample t-test, and receiver operating characteristic (ROC) curve, the efficiency of system can be evaluated. Finally, we integrated the parameters with back propagation neural network (BPNN) to improve the power of nodule recognition. Result shows that a single slice image can provided better information. From the comparison between different phases in malignant nodules CT images, significant differences were find in density (p=0.009), entropy (p=0.011), and energy (p=0.024). Comparison, There are significant differences between benign and malignant nodules of density (p=0.024), entropy (p=0.002), energy (p<0.001) and homogeneity (p=0.001) at post-contrast2 stage, and of contrast (p=0.001) at pre-contrast stage. The area under the ROC curve of density (0.725), entropy (0.762), energy (0.738) and homogeneity (0.741) are maximum at post-contrast2 stage, and of contrast (0.714) is maximum at pre-contrast stage. After repeated testing ten times, the accuracy, sensitivity, and specificity was 0.791±0.017, 0.908±0.018, 0.457±0.107, respectively for our system. In conclusion, thru the comparison of 2D textural analyses between different stages of dynamic CT image, we find that dynamic contrast enhancement could change internal composition of lung nodule. This result leads useful parameters to classify benign and malignant nodules for further development in computer aided diagnosis (CAD) system. In the future, we expect that high spatial resolution multi-detector computed tomography which creates a large amount data are used to observe that vascular enhancement character in CT image, and then diagnostic efficacy need to be evaluated by match up technique of CAD.

並列關鍵字

Computed tomography ； contrast ； lung nodule ； texture analysis

參考文獻

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肺臟腫瘤於動態顯影CT影像之特徵分析

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