Ultrasound-based tissue characterization and classification of fatty liver disease: A screening and diagnostic paradigm
Introduction
Fatty Liver (Steatosis) or Fatty Liver Disease (FLD) indicates accumulation of triglycerides (fat) in the liver. Fatty liver can occur with or without the intake of alcohol. In 1980, Ludwig et al. [76] named it as Non-Alcoholic Fatty Liver Disease (NAFLD) when the fatty liver condition is independent of alcohol intake. FLD has been associated to metabolic syndrome [127], and hence it leads to several diffuse and prevalent pathologies, such as diabetes mellitus, insulin resistance, hypertension, and dyslipidemia. The accumulation of fat in the liver may eventually lead to inflammation, condition called as alcoholic or non-alcoholic steatohepatisis (ASH or NASH) and finally to cirrhosis (which describes large scale liver degeneration associated with an increased risk of hepatocellular carcinoma [95], [116], [19]. Studies revealed that the prevalence of FLD depends on sex [99], ethnicity [37], and age [52]. Overall, FLD affects about 15% of the world population [37], [98]), and it is the most common reason for elevated liver enzymes and chronic liver disease in developed countries [18]. Early diagnosis of FLD is of paramount importance to prevent its degeneration into irreversible liver diseases, such as liver cancer [117] and acute liver failure [146]. FLD is also a major risk factor for heart attacks and stroke [138], [139]. Furthermore, advanced liver diseases result in higher health care utilization, which implies higher cost for the health care provider [14].
Even though detection of FLD is easy, the differential diagnosis of FLD is difficult [149]. In fact, FLD might be linked to different factors, such as infections, inflammations, and drug or toxin-related injuries. Hepatic steatosis is usually categorized as macrovesicular or microvesicular [149]. Macrovesicular steatosis is a common occurrence in ambulatory patients, and microvesicular steatosis is associated with severe mitochondrial injury and acute hepatic dysfunction [149]. Therefore, liver biopsy is the preferred diagnostic technique for FLD detection [100]. However, biopsy is invasive, and it causes anxiety and discomfort to patients due to pain and the possibility of bleeding/hemorrhage [80]. These complications occur in at least 1.3% of all cases and the mortality ranges from 0.1% to 0.5% [17]. Given the relatively high prevalence of FLD in the general population, minimal invasive procedures have been developed for FLD diagnosis and the assessment of its degree of severity. Among all noninvasive techniques, Ultrasound (US) is the most common and widely used imaging modality for FLD diagnosis, because it is (a) inexpensive, (b) emits no harmful radiation, (c) is widely available and (d) has high sensitivity. A major downside of this imaging modality is the operator dependability [135]. Computer Aided Diagnosis (CAD) systems have been and are being developed as adjunct techniques to reduce operator dependability and to get reproducible results [30], [39], [113], [125], [49], [144]. Therefore, developing CAD systems that detect early stage FLD is of utmost importance to: (a) save patients from unwanted anxiety, (b) increase the chance of recovery and (c) reduce the cost associated with providing treatments for advanced liver diseases [7].
In this paper, we first review the advantages and limitations of current modalities that are used for FLD detection (Section 2). Subsequently, we discuss the structure of an US-based CAD system and briefly describe the features that are extracted from the US images and the commonly used classification algorithms (Section 3). We then review the methodology and evaluation results of several CAD systems proposed in the literature (Section 4). In these techniques, first informative features are extracted from the US images. The features are used as input to train automated decision making systems. Coupling feature extraction with automated classification provides a way to evaluate the features in a practical setting, i.e. it is a way to find out how useful these features are for a working radiologist. After careful analysis of the literature, we found that the US-based CAD techniques for FLD can improve accuracy, speed and objectiveness of the diagnosis, and thereby, reduce operator dependability. We conclude the paper in Section 5.
Section snippets
Liver
The liver is the heaviest and the largest glandular organ in the human body and it is absolutely crucial to life [12]. The liver performs vital functions: synthesis of proteins, fats and fatty acids, metabolism and storage of carbohydrates, and bile production and excretion. It maintains both volume and quality of blood by filtering potentially harmful biochemical products from the blood. One of these harmful products is bilirubin, which forms during the breakdown of old blood cells [134].
Computer Aided Diagnostic (CAD) technique workflow
In this section, we present a few of the commonly used processing methods which extract informative features from US images. These features can be used in automated classification algorithms for FLD detection. Fig. 4 shows a typical system block diagram which depicts both data flow and algorithms which act on the data. The following sections provide a short discussion of these algorithms.
Review of published cad studies for FLD diagnosis
In this section, we review selected CAD based studies for FLD diagnosis.
Conclusion
Generally, US-based diagnosis of FLD is subjective in nature because it depends to a large extend on the skills and experience of the physicians. In this review, we established the need for computer based FLD diagnosis systems by reviewing the advantages and disadvantages of several currently used diagnostic modalities. Subsequently, we described techniques and algorithms used in the individual stages of a CAD system, namely feature extraction, feature selection, and classification. We also
References (153)
- et al.
Transient elastography in non-alcoholic fatty liver disease
Ann Hepatol
(2012) - et al.
Automated diagnosis of epileptic EEG using entropies
Biomed. Signal Proc. Control
(2012) - et al.
Role of liver biopsy and serum markers of liver fibrosis in non-alcoholic fatty liver disease
Clin. Liver Dis.
(2007) - et al.
Fuzzy logic algorithm for quantitative tissue characterization of diffuse liver diseases from ultrasound images
Int. J. Med. Inform.
(1999) - et al.
Impact of fatty liver disease on health care utilization and costs in a general population: a 5-year observation
Gastroenterology
(2008) Liver biopsy in elevated liver functions tests? An old question revisited
J. Hepatol.
(2001)Non-alcoholic steatohepatitis and cancer
Clin. Liver Dis.
(2007)Non-invasive diagnosis of steatosis and fibrosis
Diabetes Metab.
(2008)Computer-aided diagnosis in medical imaging: historical review, current status and future potential
Comput. Med. Imaging Graph.
(2007)- et al.
Computer-aided diagnosis: the emerging of three CAD systems induced by Japanese health care needs
Comput. Methods Programs Biomed.
(2008 Dec)