Liver fat content determined by magnetic resonance imaging and spectroscopy

Abstract

Hepatic steatosis as the most prevalent liver disorder can either be related to alcoholic liver disease (ALD) or non-alcoholic fatty liver disease (NAFLD). In both conditions, hepatocytes excessively accumulate fat-containing vacuoles within their cytoplasm, which is the key histological feature. In contrast to ALD, NAFLD is commonly associated with metabolic syndrome, obesity and insulin resistance. To determine increased liver fat content, liver biopsy is currently considered the gold standard. Besides the invasive technique, various other non-invasive techniques have been developed, such as ultrasound, computed tomography (CT), magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) based methods. Among these techniques, ultrasound and CT provide only qualitative information about hepatic steatosis, whereas MRS- or MRI-based methods are able to determine even small amounts of fat accurately. These non-invasive magnetic resonance techniques have already proven their great potential, especially in longitudinal and cross-sectional studies regarding various metabolic conditions and medical treatment regimens. In this review, the most common, non-invasive MRS/MRI techniques for assessment of intrahepatic lipid content are described with their inherent advantages and limitations.

Figure 1

T1-weighted gradient echo images recorded with OP (parts A and C) and IP (B and D) conditions. A and B show a lean subject with almost equal signal intensity of the liver under OP (A) and IP (B) conditions, since no intrahepatic lipid storage is present. In contrast, C and D show an obese subject with lower signal intensity under OP conditions compared to IP conditions, which indicated relevant intrahepatic lipid storage.

Figure 2

A and B show fat-selective spectral-spatial imaging of the body trunk. A lean subject with almost no intrahepatic lipid storage (A) and an obese subject with markedly increased lipid storage in the liver parenchyma is shown (B).

Figure 3

Three subjects with different intrahepatic lipid contents are compared. The subject in row (a) shows intrahepatic lipid content of about 20%; the subject in row (b) shows intrahepatic lipid content of about 10%; and the subject in row (c) shows intrahepatic lipid content in the normal range (about 1%). The figure shows IP (column I) and OP (column II) images of a T1-weighted gradient echo sequence. Column III shows the results of a fat-selective spectral-spatial imaging sequence, and column IV shows the results from single-volume ¹H-MRS using a STEAM sequence.