The Role of Recent MRI Applications in Differentiation of Hepatic Focal Lesions

Abstract

Summary L iver lesions can be classified on the basis of both unenhanced and contrast-enhanced images. On unenhanced imaging, classification can be based upon the signal intensity and delineation of lesions on conventional T2-weighted and T1- weighted images as well as on opposed phase T1- weighted images or T1-weighted images acquired with fat suppression. Thus, on unenhanced imaging, lesions with a high fluid content, lesions containing fat and lesions with internal hemorrhage can be detected and readily diagnosed. Unfortunately, unenhanced imaging alone cannot always differentiate reliably between benign and malignant lesions and in many cases, additional information from contrast-enhanced imaging is necessary for accurate differential diagnosis (Grazioli et al., 2009). The availability of contrast agents with markedly different properties means that lesions can be classified on the basis of different enhancement patterns on contrast-enhanced imaging. Thus, lesions can be classified according to their behavior on dynamic imaging following the administration of extra cellular contrast agents (in a similar manner to that which occurs on dual phase spiral CT imaging), and to their behavior on delayed imaging following the administration of contrast agents targeted either to the hepatocytes or the Kupffer cells. In the dynamic phase of contrast enhancement after the administration of gadolinium-based contrast agents, lesions can be classified according to whether they demonstrate hyper vascular or hypo vascular enhancement patterns or delayed persistent enhancement on T1-weighted acquisitions during the arterial, portal-venous and equilibrium phases, respectively. Within these three major groups of lesions, lesions can be classified further according to the presence or absence of certain characteristic features. For example, a central scar within a hyper vascular lesion in a non cirrhotic liver that shows low signal intensity on Tl-weighted images and high signal intensity on T2-weighted images may be indicative of FNH. Similarly, a hypo vascular lesion with a hyper vascular rim that shows contrast agent washout at 10-15 min post-injection and halo sign on T2-weighted images may be indicative of a metastasis of adenocarcinoma. Finally, a lesion that shows nodular enhancement in the arterial phase followed by centripetal filling-in in the subsequent phases and high signal intensity on T2 Weighted images may be indicative of a haemangioma (Schneider et al., 2010).