Caren van Roekel

22 Chapter 2 2.3 Imaging Before treatment, it is essential to perform cross-sectional imaging of the patient, to identify all sites of (metastatic) disease and to assess the vascular anatomy. For this purpose, various imaging modalities can be used. 2.3.1. Liver CT/MRI and 18 F-FDG-PET In general, three-phase CT images are made: late arterial phase for the detection of hypervascular tumors, a portal venous phase for the detection of hypovascular tumors and a late venous phase for the detection of wash-out (22). An early arterial phasemay be preferable for vascular evaluation in thework-up for radioembolization. Compared to the late arterial phase, the contrast-to-noise ratio of the hepatic artery relative to the portal vein is higher in this early arterial phase (23). MRI is superior to CT in terms of soft tissue contrast, but inferior regarding the detection of small arteries, due to the higher resolution of CT. Dynamic contrast-enhanced sequences can be used to assess tumor hypervascularity and washout in a large number of phases. Diffusion weighted and T2-weighted imaging provide options for high sensitivity tumor detection. The added value of 18 F-FDG-PET-imaging in the workup for radioembolization is widely accepted. The most important benefit in the workup is the visualization of extrahepatic disease. The study of Rosenbaum et al. have found a change of management in 17% of patients with metastatic colorectal carcinoma, based on imaging with 18 F-FDG-PET (24). Metastases from uveal melanoma, breast cancer, colorectal carcinoma are generally FDG-avid. HCC, however, accumulates FDG to varying degrees, limiting the sensitivity of PET for primary tumors (25). Despite this lower sensitivity, the studies of Nagaoka et al. and Cho et al. show that 18 F-FDG-PET does have a role in initial staging of hepatocellular carcinoma (26, 27). Well-differentiated HCC lesions show very little uptake on 18 F-FDG-PET imaging, whereas poorly differentiated HCCs show much more uptake. Park et al. have reported that patients with 18 F-FDG-positive tumors have lower survival compared to patients with 18 F-FDG-negative tumors (28). Thus, 18 F-FDG-PET may be useful for characterization of cancer biology(29). Over 90% of gastroenteropancreatic neuroendocrine tumors have high concentrations of somatostatin receptors. A 68-gallium-labelled somatostanin