Received 28 February 2013, revised 6 July 2013, online published 25 September 2013 Defence Science Journal, Vol. 63, No. 5, September 2013, pp. 478-486, DOI : 10.14429/dsj.63.3951  2013, DESIDOC NOMENCLATURE B-Mode US B-Mode Ultrasound: Brightness-Mode ultrasound is a two dimensional representation of echo-producing interfaces in a single plane. FLL Focal Liver Lesion: Focal liver lesion refers to area of liver tissue damage. Benign FLL Benign Focal Liver Lesion: Non-cancerous focal liver lesion. Malignant FLL Malignant Focal Liver Lesion: Cancerous focal liver lesion. HFLL Hyperechoic Focal Liver Lesion: The focal liver lesion with more echogenicity as compared to the surrounding liver parenchyma. Isoechoic FLL Isoechoic Focal Liver Lesion: The focal liver lesion with same echogenicity as that of the surrounding liver parenchyma. HFLL Hypoechoic Focal Liver Lesion: The focal liver lesion with less echogenicity as compared to the surrounding liver parenchyma. Anechoic FLL Anechoic Focal Liver Lesion: The focal liver lesion which appears without echoes on ultrasound. Typical FLL Typical Focal Liver Lesion: Focal liver lesions with classic diagnostic sonographic appearance. Atypical FLL Atypical Focal Liver Lesion: Focal liver lesion with non-specifc sonographic appearance. NOR Normal Liver: Normal liver has homogeneous texture with medium echogenicity (i.e. same or slightly increased echogenicity compared to the right kidney). CYST Liver Cyst: Abnormal fuid flled sacs in the liver. Typical Cyst Typical Cyst: Well defned, round, anechoic lesion with posterior acoustic enhancement and thin imperceptible wall. Atypical Cyst Atypical Cyst: Appear with irregular, thickened wall and internal echoes. HEM Hemangioma: The most common primary benign focal liver lesion. Typical HEM Typical Hemangioma: Appear as a well circumscribed uniformly hyperechoic lesion. Atypical HEM Atypical Hemangioma: Appear as isoechoic or even hypoechoic lesion. HCC Hepatocellular Carcinoma: The most common primary malignant focal liver lesion. SHCC Small Hepatocellular Carcinoma: HCC lesions (<2cms), appearance vary from hypoechoic to hyperechoic lesions. LHCC Large Hepatocellular Carcinoma: HCC PCA-SVM based CAD System for Focal Liver Lesions using B-Mode Ultrasound Images Jitendra Virmani * , Vinod Kumar, Naveen Kalra # , and Niranjan Khandelwal # Indian Institute of Technology Roorkee, Roorkee - 247 667, India # Post Graduate Institute of Medical Education and Research, Chandigarh -160 012, India * E-mail: jitendra.virmani@gmail.com ABSTRACT The contribution made by texture of regions inside and outside of the lesions in classifcation of focal liver lesions (FLLs) is investigated in the present work. In order to design an effcient computer-aided diagnostic (CAD) system for FLLs, a representative database consisting of images with (1) typical and atypical cases of cyst, hemangioma (HEM) and metastatic carcinoma (MET) lesions, (2) small as well as large hepatocellular carcinoma (HCC) lesions and (3) normal (NOR) liver tissue is used. Texture features are computed from regions inside and outside of the lesions. Feature set consisting of 208 texture features, (i.e. 104 texture features and 104 texture ratio features) is subjected to principal component analysis (PCA) for fnding the optimal number of principal components to train a support vector machine (SVM) classifer for the classifcation task. The proposed PCA-SVM based CAD system yielded classifcation accuracy of 87.2% with the individual class accuracy of 85%, 96%, 90%, 87.5% and 82.2% for NOR, Cyst, HEM, HCC and MET cases respectively. The accuracy for typical, atypical, small HCC and large HCC cases is 87.5%, 86.8%, 88.8%, and 87% respectively. The promising results indicate usefulness of the CAD system for assisting radiologists in diagnosis of FLLs. Keywords: Focal liver lesions, B-mode ultrasound, principal component analysis, support vector machine classifer, computer-aided diagnostic system 478