An ultrasonic image evaluation system for assessing the severity of chronic liver disease

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Abstract

A quantitative ultrasonic image evaluation system that generates a numerical severity measurement to assess the progression of chronic liver disease and assist clinical diagnosis is proposed in this paper. The progression of chronic liver disease is closely related to the amount of fibrosis of the liver parenchyma under microscopic examination. The powerful index, computer morphometry (CM) score developed in Sun et al. [Sun YN, Horng MH, Lin XZ. Automatic computer morphometry system techniques and applications in medical diagnosis. In: Cornelius TL, editor. Computational methods in biophysics, biomaterials, biotechnology and medical systems. Algorithm development, mathematical analysis and diagnostics, vol. 4. Boston/Dordrecht/London: Kluwer Academic Publishers; 2003. p. 33–50], accurately measures the fibrosis ratio of liver parenchyma from a microscopy of human liver specimens. Therefore, the results of the CM score of patients serves as an assessment basis for developing the disease measurement of the B-mode liver sonogram under echo-texture feature analysis methods. The radial basis function (RBF) network is used to establish the correlates between texture features of ultrasonic liver image and the corresponding CM score. The output of the RBF network is called the ultrasonic disease severity (UDS) score. The correct classification rate of 120 test images by using the UDS score is 92.5%. These promising results reveal that the UDS is capable of providing an important reference to diagnose chronic liver disease.

Introduction

In clinical diagnosis, liver disease is taken seriously because liver is a vital organ in the human body. Liver diseases can be divided into two main categories, focal disease (e.g. hepatoma, hemangioma) and diffused diseases (e.g. hepatitis, cirrhosis). The focal diseases are where the abnormality is concentrated in a small area of liver tissue, whereas diffused disease is where the abnormality is distributed all over the liver volume. Chronic liver disease is frequent among diffused liver diseases. The severity of the disease on inflicted patients may range from a healthy carrier to hepatitis, and more serious to cirrhosis. Liver biopsy is the standard clinical routine for diagnosing chronic liver disease and for guiding and monitoring treatment [1], [2]. However they are associated with morbidity (3%) and mortality (0.03%). Therefore, developing a reliable, non-invasive and quantitative disease scoring system using a B-mode liver sonogram for evaluating histological changes is highly promising in diagnosing and monitoring chronic liver diseases.

The texture-based measures have been applied to ultrasound images over a decade. Richard and Keen extracted the micro-texture features using the Laws’ 5-by-5 feature masks and then applied the probabilistic relaxation algorithm to the segmentation of ultrasound images of the prostate [3]. Nicholas et al. used textural features of B-scan images to classify livers and spleens of normal humans [4]. Wu et al. applied a multi-resolution fractal feature vector and compared it with other texture measures to distinguish hepatoma, cirrhosis, and a normal liver [5]. Pavlopoulos et al. evaluated the performance of different texture analysis techniques for a quantitative characterization of ultrasonic liver images [6]. Bleck et al. used the autoregressive periodic random field model to classify normal and fatty liver, hepatitis and cirrhosis [7]. Mojsilivis et al. adopted the nonseparable wavelet transform to discriminate between the states of normal, steatosis and cirrhosis [8]. Gebbinck et al. and Kadah et al. applied discriminate analysis with a neural network to discriminate between various types of diffused liver diseases, such as disease of a fatty, cirrhotic, and normal liver [9], [10]. Pavlopoulos et al. applied the fuzzy neural network to classify liver states by using features of different texture analysis methods including gray-level difference statistics, gray-level run-length statistics, a spatial gray-level dependence matrix, and the fractal dimension [11]. This study classified the diseases of fatty, cirrhotic, and normal liver. Horng et al. compared the effectiveness of texture descriptors that include the gray-level co-occurrence matrix, the fractal dimension, the texture spectrum, the statistical feature matrix, and the texture feature coding method in classifying chronic liver diseases that are normal liver, hepatitis and cirrhosis [12]. The results of our past work [12] reveal that the features generated from the gray-level co-occurrence matrix (GLCM) [18] and texture feature coding method (TFCM) were effective for classifying the three liver states. As a result, two methods are used to select texture features for assessing the severity of chronic liver disease and discussed in this paper.

Unlike the above-mentioned literature on the classification of ultrasonic liver images, the goal of this paper is to develop a scoring system for measuring the progression of chronic liver diseases. The key to establishing the scoring system is to find the texture features that are highly correlated with the progression of liver disease. The progression of liver disease, from normal to liver hepatitis and more serious to cirrhosis, depends on the amount of fibrosis of the liver specimens from the histological view. In clinical diagnosis, Knodell's score [13] was broadly used to measure liver fibrosis when physicians observed the patient's specimens in a microscopy in the last two decades. It recorded only five discrete numerical scores for staging liver fibrosis, based on the physician's observation. Obviously, it was not enough and nor suitable for developing a quantitative progression index for the assessment of the liver disease. Alternatively, as reported in [14], [15], we proposed a quantitative index, called a computer morphometry (CM) score, which was more reliable and effective than the conventional Knodell's score for evaluating the amount of liver fibrosis. Therefore, the CM scores are used herein as the criteria for selecting powerful texture features.

The powerful ultrasonic scoring system should generate a disease severity score that matches the corresponding CM score as closely as possible. The correlates between the selected texture features and the corresponding CM score is intrinsic a multivariate regression problem. The radial basis function network is herein used to solve this multivariate regression [16]. The output of the radial basis function network is denoted to the ultrasonic disease severity (UDS) scores. Besides, the intervals of UDS scores in different liver states are also determined as standards for classification. Experiments with 40 training images demonstrate that the UDS scores generated from this system are significantly correlated to the CM scores of corresponding biopsy specimens. In addition, 120 test ultrasonic liver images were used to analyse the classification capability. The resulting correct classification rate reaches as high as 92.5%. These results reveal the proposed system of a UDS score has promising potentiality to provide valuable satisfactory reference for the diagnosis of chronic liver disease.

Section snippets

Ultrasonic liver image acquisition

A Toshiba Sonolayer SSA 250A sector scanner ultrasonic machine with the transducer PVE375A 3.75 MHz obtained the ultrasound images used in this study. A VFG frame grabber card on an IBM-PC was used to capture image frames with 512 × 512 spatial resolutions and 8 bits/pixel intensity quantification. Physicians through specially designed programs could manipulate the image acquisition. A number of software tools were developed on this system to allow physicians to define the ROI in the image and

Experimental results and discussion

In this study, we have developed an ultrasonic scoring system to assess the severity of chronic liver disease. The system integrates the techniques of texture analysis of a liver sonogram with the corresponding pathological CM score measurement. In this system, all programs are encoded by Visual C++ version 6.0 with a Pentium personal computer in a Microsoft Windows 2000 environment. The system provides user-friendly interfaces and efficient computation for real-time clinical evaluation. In the

Conclusion

This paper proposes a quantitative ultrasonic scoring system for assessing the chronic liver disease by analysing the characteristics of liver echo-texture. It not only generates quantitative indices to assess liver disease progression and also classify the disease states of ultrasonic liver images. This new quantitative index is called the ultrasonic disease severity (UDS) score. In clinical diagnosis, the amount of liver fibrosis is one of the key factors used to assess the progression of

Acknowledgment

The authors would like to thank the National Science Council, ROC NSC 93-2213-E-251-001 for support of this work.

Ming-Huwi Horng received the B.S. degree in Mathematics from National Cheng Kung University, Taiwan, in 1990 and the M.S. and Ph.D. degrees in Information Engineering form National Cheng Kung University in 1992 and 1997, respectively. He is currently associate professor at the Department of Information Technology, National PingTung Institute of Commerce. His research interests focus on medical image processing, evolutionary algorithm, pattern recognition and bioinformatics. He is a member of

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Ming-Huwi Horng received the B.S. degree in Mathematics from National Cheng Kung University, Taiwan, in 1990 and the M.S. and Ph.D. degrees in Information Engineering form National Cheng Kung University in 1992 and 1997, respectively. He is currently associate professor at the Department of Information Technology, National PingTung Institute of Commerce. His research interests focus on medical image processing, evolutionary algorithm, pattern recognition and bioinformatics. He is a member of Chinese Association of Biomedical Engineering, IEEE and Chinese Association of Image Processing and Pattern Recognition.

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