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BACKGROUND AND PURPOSE: PET/MRI with 18 F-FDG has demonstrated the advantages of simultaneous PET and MR imaging in head and neck cancer imaging, MRI allowing excellent soft-tissue contrast, while PET provides metabolic information. The aim of this study was to evaluate the added value of gadolinium contrast-enhanced sequences in the tumor delineation of head and neck cancers on 18 F-FDG-PET/MR imaging. MATERIALS AND METHODS:Consecutive patients who underwent simultaneous head and neck 18 F-FDG-PET/MR imaging staging or restaging followed by surgery were retrospectively included. Local tumor invasion and lymph node extension were assessed in 45 head and neck anatomic regions using 18 F-FDG-PET/MR imaging by 2 rater groups (each one including a radiologist and a nuclear medicine physician). Two reading sessions were performed, one without contrast-enhanced sequences (using only T1WI, T2WI, and PET images) and a second with additional T1WI postcontrast sequences. The results were compared with the detailed histopathologic analysis, used as reference standard. The k concordance coefficient between the reading sessions and sensitivity and specificity for each region were calculated.

This review shows the images obtained with non-contrast MR lymphography in different pathologic conditions affecting the liver. Non-contrast MR lymphography is obtained with a free-breathing 3D high spatial resolution fast-recovery fast spin-echo sequence similar to that used for 3D MR cholangiopancreatography. The liver is the largest lymph-producing organ generating approximately half of the body's lymphatic fluid, and is the most important part of the lymphatic system from a functional point of view. Therefore, understanding the anatomy, physiology, and physiopathology of the lymphatics of the liver is important. However, its anatomy and pathology are relatively unknown because of the absence of commonly used imaging techniques. We describe the anatomy, the physiology, and the pathophysiology of the lymphatic system of the liver and the possibility of identifying dilated lymphatic vessels in various liver diseases and conditions. Disruption of normal lymphatic structure and function is observed in various disease conditions. Liver lymph flow is directly correlated with portal venous pressure. Therefore, a dilatation of liver lymphatics is observed in portal hypertension as well as in increased pressure in hepatic veins. After liver transplantation, ligation of lymphatic vessels at the hilum reduces chylous ascites and results in lymphatic dilatation which is easily observed. In severe long-standing biliary stenosis, dilated lymphatic vessels are commonly demonstrated with non-contrast MR lymphography. In hepatocellular carcinoma, intrahepatic cholangiocarcinoma, and some metastases, lymphatic vessels are abundant in the immediate vicinity of the tumour. These various lymphatic abnormalities can be demonstrated with non-contrast MR lymphography.