Computer-aided diagnosis of liver tumors on computed tomography images
Introduction
Liver cancer is the tenth most common cancer and the fifth and ninth most common causes of cancer death in men and women, respectively, in the USA [1]. Many cancers have a high survival rate if detected and treated early [2]. Computed tomography (CT) is one of the most common and robust imaging techniques for the detection of liver tumors [3]. CT provides images of the whole liver through multiphase sequential scans after the injection of contrast media [4].
Several studies have discussed CAD systems for liver tumors using CT images [5], [6], [7]. Chen et al. [5] reported a CAD system that used boundary detection to automatically identify the contours of the liver, and a neural network (NN) classification system using a spatial grey-level co-occurrence matrix (SGLCM) [8], [9] to distinguish a normal liver and two types of liver tumors, hepatoma and hemangioma. Gletsos et al. [7] used average gray levels and 48 texture characteristics with three hierarchically placed feedforward NNs to classify tumors into healthy, cyst, hemangioma, and hepatocellular carcinoma groups, however segmentation of the tumors was done manually using regions of interest. In the study by Zhang et al. [6], the authors used an automatic edge detection and subtraction process [10] to detect hepatocellular carcinoma and a 3-layer feedforward NN to differentiate the degree of cirrhosis in the liver, which was derived by integrating two shape and seven grey-level co-occurrence matrix (GLCM) texture features [8].
This study developed a computer-aided diagnosis (CAD) system with semi-automatic region growing segmentation technique. Three kinds of features were extracted for analyzing between benign and malignant, including features of texture [11], [12], [13], [14], shape [15], [16], [17], [18], and kinetic curve [19], [20], [21]. Texture was quantified using GLCM [8] including the relative position and density of the tumor. Shape was classified using an elliptic model [17], [18], and a kinetic curve was generated to represent changes in density between each phase on the CT images. To simplify the kinetic curve, we used the four features proposed by Chen et al. [20], [22] including maximum enhancement, time to peak, uptake rate, and washout rate.
Section snippets
CT scans
This retrospective study was approved by the institutional review board at our hospital and the requirement for informed consent was waived. The data used in this study were acquired from two CT scanners (Brilliance iCT 256, Philips Healthcare, Dutch; SOMATOM Definition AS+, Siemens Healthcare, German) with 100, 120, or 130 kV, automatic mA control, and without extra noise reduction processes. The parameters of the CT images were as follows: slice thickness 0.7 mm–1.5 mm, and image size
Methods
In this study, the CAD system was comprised of five parts: tumor segmentation, tumor registration, feature extraction, and tumor classification. The tumor region was segmented by using a region growing method [23] on the CT phase which is the most conspicuous focal liver lesion selected by one author (C.C.C. with 10 years of experience in the diagnosis of abdominal imaging). Subsequently, a tumor registration method was performed manually to align the tumor between each phase. Three kinds of
Results
The comparison of texture, shape, and kinetic curve features between benign and malignant tumors is listed in Table 2. For texture features, six features (G1, G4, G8, G9, G12, and G14) showed significant differences (p < 0.05) between the benign and malignant tumor. Compared with the benign tumors, the malignant tumors are relative larger in size and more spiculated (significant higher values of R and Rs). For the kinetic curve features, none of the four features were statistically
Discussion
Proliferation is the main property of tumors, especially malignant ones [33]. Further, angiogenesis is important since the proliferation of cancer cells which generates capillaries from the existing vessel for supplying nutrients [34], [35]. In this study, the intra-tumor texture generated from the immature and tortuous new capillaries [35] was quantified by GLCM texture analysis. To quantify the tumor shape, an ellipsoid fitting model was established and a series of morphological properties
Funding
The authors thank the Ministry of Science and Technology (MOST104-2221-E-002-062-MY3) of the Republic of China for the financial support.
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