A comparative study of computer-aided classification systems for focal hepatic lesions from B-mode ultrasound

Abstract

A comparative study of three computer-aided classification (CAC) systems for characterization of focal hepatic lesions (FHLs), such as cyst, hemangioma (HEM), hepatocellular carcinoma (HCC) and metastatic carcinoma (MET), along with normal (NOR) liver tissue is carried out in the present work. In order to develop efficient CAC systems a comprehensive and representative dataset consisting of B-mode ultrasound images with (1) typical and atypical cases of cyst, HEM and MET lesions, (2) small and large HCC lesions and (3) NOR liver cases have been used for designing K-nearest neighbour (KNN), probabilistic neural network (PNN) and a back propagation neural network (BPNN) classifiers. For differential diagnosis between atypical FHLs, expert radiologists often visualize the textural characteristics of regions inside and outside the lesion. Accordingly in the present work, texture features and texture ratio features are computed from regions inside and outside the lesions. A 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 dimensionality reduction; it is observed that maximum accuracy of 87.7% is obtained for a PCA-BPNN-based CAC system in comparison to 86.1% and 85% as obtained by PCA-PNN and PCA-KNN-based CAC systems. The sensitivity of the proposed PCA-BPNN based CAC system for NOR, Cyst, HEM, HCC and MET cases is 82.5%, 96%, 93.3%, 90% and 82.2%, respectively. The sensitivity values with respect to typical, atypical, small HCC and large HCC cases are 85.9%, 88.1%, 100% and 87%, respectively. Keeping in view the comprehensive and representative dataset used for designing the classifier, the results obtained by the proposed PCA-BPNN-based CAC system are quite encouraging and indicate its usefulness to assist experienced radiologists for interpretation and diagnosis of FHLs.

Neural Network Ensemble Based CAD System for Focal Liver Lesions from B-Mode Ultrasound

“…Typical Cyst appears as round, anechoic lesion with posterior acoustic enhancement and well defined thin imperceptible wall [5,9,10,21]. HEM is the most common primary benign FLL [1,7,9,17,22]. Almost 70 % of all the HEM cases encountered in routine practice are typical HEMs.…”

“…Almost 70 % of all the HEM cases encountered in routine practice are typical HEMs. Typical HEM appears as a well circumscribed uniformly hyperechoic lesion [5,9,10,15,[21][22][23]. MET is the most common secondary malignant FLL [2,7,9,[21][22][23].…”

“…MET may occur singly or as multiple deposits of varying sizes. The typical sonographic appearance of MET lesion is the 'target' or 'bull's-eye' appearance (i.e., hypoechoic center surrounded by a hyperechoic rim) [2,5,7,15,16,21,22,24]. The sample images for NOR liver and typical cases of Cyst, HEM and MET lesions are shown in Fig.…”

“…Differential diagnosis of Cystic MET and atypical Cyst from conventional gray scale B-mode US can be quite challenging [21,22]. Atypical HEMs are a great mimic and definite diagnosis with conventional gray scale B-mode US is difficult [9].…”

“…Atypical MET lesions can appear with extremely variable sonographic appearances ranging from anechoic, hypoechoic, isoechoic, hyperechoic and even with mixed echogenicity [5, 8-10, 23, 24]. Differentiating atypical MET lesions from HCC lesions and HEM lesions is considerably difficult [9,11,16,[21][22][23]25].…”