結合Nakagami 參數和輪廓特徵進行乳房超音波的腫瘤分類

Combine Nakagami parameter and edge feature to classify breast masses by ultrasound

廖尹吟(Yin-Yin Liao)

指導教授 ： 葉秩光

國立清華大學/原子科學院/生醫工程與環境科學系/碩士(2009年)

摘要

因應東方女性罹患乳癌的比例日漸攀升，為了提升早期的治癒率，影像診斷系統扮演不可或缺的角色，針對東方女性的乳房較小巧且緻密而言，比起西方女性更依賴於乳房超音波的診斷。目前雖有許多研究利用乳房超音波的電腦輔助診斷系統幫助醫師辨別乳房腫瘤，但此方法仍會受限於儀器和人為操作因素；另有一派學者提出分析乳房超音波的原始射頻訊號，已證實Nakagami 分佈可描述乳房超音波訊號特性，也能有效區分良性和惡性的腫瘤，但仍未有較完整的一套方法，且Nakagami 參數影像的解析度較差。
因此，我們希望結合灰階影像的輪廓特徵和原始射頻訊號的資訊做為新的診斷工具，由灰階影像可以獲取乳房腫瘤的外型，而Nakagami 參數影像則可以區分腫瘤內部的成分，由不同的物理量一起探討乳房腫瘤的分類。傳統B-mode 影像前置處理，我們提出新的參數MSR(Mean to Standard deviation Ratio)做為增強灰階影像對比的加權因子，且發現MSR 的分佈能夠區分乳房病灶和正常乳腺組織，便採用雙峰高斯分佈擬合其直方圖，以最佳整體臨界值法獲取二值化影像，再利用增強對比後的灰階影像和二值化影像進行自動化輪廓圈選，最後，萃取腫瘤輪廓並採用6 種輪廓特徵參數，驗證其惡性腫瘤的輪廓不規則度會高於良性腫瘤。另一方面，針對Nakagami 參數進行探討，採用先前研究提出的Nakagami參數成像方法，並觀測不同乳房病灶其Nakagami 參數影像上ROI 內的平均Nakagami 參數，可以區分出纖維囊腫、脂肪、及實質性腫瘤，且統計出良性腫瘤的平均Nakagami 參數會高於惡性腫瘤。
利用Fuzzy C-means 執行所有特徵參數的群聚分析，證實結合輪廓特徵參數和Nakagami 參數的方法分類乳房腫瘤，兩者之間可以相輔相成，表現最好的輪廓特徵參數和平均Nakagami 參數結合後，其診斷效率的準確度為81.7%、敏感度為80%、特異性為83%。

關鍵字

乳房超音波 ； 輪廓特徵 ； Nakagami 參數影像 ； 乳房腫瘤分類

並列摘要

Breast cancer is the most common cancer in women worldwide. According to the lately statistics in Taiwan, the mortality from breast cancer has become the fourth of cancerous diseases among women. In addition, younger women tend to have dense breasts and Asian women tend to have denser ones. Not only ultrasound is capable of detecting masses even in dense breasts, but also more convenient, safer, and forming the images in real-time tool for patient in regularly physical examination. Computer-aided diagnosis (CAD) has been used to discriminate between benign and malignant tumor for ultrasonic B-mode scans, but this method makes the classification largely dependent on the skill of the operator. Several studies have shown that the Nakagami parameter estimated from the ultrasonic backscattered signals can be used to assist conventional B-mode scanning when classifying breast tumors.
Hence, we propose to combine ultrasonic B-mode scans with Nakagami parametric image for categorizing breast masses. We expect to acquire boundary feature and internal components of breast masses from B-mode scans and Nakagami parametric image. For boundary feature, irregular degree of contour in malignant tumor is higher than benign tumor. For internal components, the average Nakagami parameter of malignant tumor is lower than benign tumor.
We used Fuzzy C-means (FCM) to separate malignant cluster and benign cluster by all parameters. The average Nakagami parameter and contour features provide complementary characteristics in diagnosis ultrasound breast tumor image. The best efficiency is that accuracy is 81.7 %, sensitivity is 80 %, and specificity is 83 %.

並列關鍵字

Breast ultrasound ； Contour feature ； Nakagami parametric image ； Breast tumor classification

參考文獻

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