Diffuse Liver Disease: Strategies for Hepatic CT and MR Imaging

Abstract

The liver plays several complex but essential roles in the metabolism of amino acids, carbohydrates, and lipids, as well as synthesis of proteins. The basic pathophysiology of diffuse parenchymal hepatic diseases usually represents a failure in one of these metabolic pathways. Specific parenchymal diseases can be categorized as storage, vascular, and inflammatory diseases. Cross-sectional hepatic imaging techniques, specifically multidetector computed tomography (CT) and magnetic resonance (MR) imaging, have roles in evaluation of diffuse liver disease. The prominent role of multidetector CT is primarily defined by its excellent morphologic visualization capabilities, in particular of diffuse or focal intrahepatic lesions as well as of anatomic relationships between the liver and adjacent organs. The variety of available multidetector CT scanners covers a huge spectrum of detector configurations ranging from equally sized and equally spaced detector arrays to asymmetric detector configurations, resulting in imaging protocols with unique parameters for almost each multidetector CT system. In addition to 64-detector row imaging, hepatic multidetector CT can be performed with emerging techniques such as dual-energy CT. Hepatic MR imaging has been proved to be a comprehensive modality for assessing the morphology and functional characteristics of the liver. Concurrent technical improvements as well as implementation of advanced imaging sequence designs permit high-quality examination of the liver with T1-, T2-, and diffusion-weighted pulse sequences. Three basic demands remain if MR imaging is chosen for hepatic imaging: to improve parenchymal contrast, to suppress respiratory motion, and to ensure complete anatomic coverage. Supplemental material available at http://radiographics.rsna.org/content/29/6/1591/suppl/DC1.

Quantification of liver iron content with CT—added value of dual-energy

“…In vivo human liver shows a normal variation of attenuation values at unenhanced SECT ranging from 55 to 65 HU [7]. Our ex-vivo experiments are in keeping with these values by showing a range of healthy veal liver tissue from 58 to 66 HU.…”

“…Fat results in a decrease in attenuation of the hepatic parenchyma confounding the effect of iron. Therefore, SECT shows a lack of sensitivity for iron detection and underestimation of LIC in the presence of fat [7,9]. Our results underline these shortcomings by demonstrating the inability of SECT to quantify LIC even at low fat concentrations of 10%.…”

“…To test for the confounding effect of co-existing fat, another 12 test tubes were prepared containing healthy liver and iron mixtures of iron concentrations at 140, 200 and 600 μmol/g simulating mild, moderate and severe haemosiderosis [1], and additional fat (goose fat) at concentrations of 0%, 10%, 30% and 50% simulating no, mild, moderate and severe steatosis [7].…”

“…This shortcoming is most evident in patients with only a mild iron overload. Moreover, CT fails to detect and quantify iron in the liver in the case of co-existing fat, which shows an inverse effect on attenuation by lowering the CT numbers [7].…”

Expectations from imaging for pre-transplant evaluation of living donor liver transplantation

“…The attenuation value of normal liver on unenhanced CT ranges between 55 and 65 Hounsfield units (HU) and is generally at least 8 HU higher relative to the spleen; the liver is regarded as fatty when the liver attenuation is at least 10 HU less than the spleen [59] . This method has high sensitivity (88%-95%) and specificity (90%-99%) [60] . Liver attenuation values also reflect the severity of fatty change.…”