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The assessment of hepatobiliary and pancreatic tumors is commonly achieved by ultrasound, computed tomography (CT), and magnetic resonance. The 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) detects increased glucose metabolism associated with neoplastic lesions, provides high accuracy in most cancer imaging applications and is now widely used in clinical practice. However, PET is not always useful and accurate knowledge of appropriate indications is essential for a proper clinical management. (18)F-FDG is transported into cells and phosphorylated by the enzyme hexokinase to (18)F-FDG-6-phosphate, which cannot proceed down the glycolytic pathway and therefore is accumulated in the malignant tissue. PET allows accurate quantification of FDG uptake in tissue, and previous studies have demonstrated that standardized uptake values provide highly reproducible parameters of tumor glucose use (Weber et al., J Nucl Med 40:1771-1777, 1999). The recent development and diffusion of hybrid PET-CT scanners allows functional and anatomic data to be obtained in a single examination, improving lesion localization and resulting in significant diagnostic improvement (Wahl, J Nucl Med 45:82S-95S, 2004). Moreover, CT can be performed diagnostically with the use of intravenous and oral contrast and simultaneous PET-contrast-enhanced CT scanning appears to be an efficient method in cancer evaluation. However, in most centers, a low-dose CT is routinely performed without contrast media infusion.Proper patient preparation, scanning protocol, combined assessment of PET and CT data, and the evaluation of conventional imaging findings are essential to define disease and to avoid diagnostic pitfalls. The role of PET and PET-CT in malignancies of the liver, biliary tract, and pancreas is here reviewed; normal patterns, representative cases, and common pitfalls are also presented. [ABSTRACT FROM AUTHOR]

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We present one of the simplest theory of nonlinear viscoelasticity taking into account stress relaxation. The model is a 3D nonlinear generalization of the standard three-parameter model of 1D classical viscoelasticity. In the framework of this theory, we examine some simple deformations. First of all, we consider a homogeneous deformation as a possible idealization of the usual triaxial test. By this analysis, we show that the model under investigation may be interesting to describe the mechanical behavior of materials like bitumen and hot mix asphalt. Moreover, we investigate the evolution of shearing motions (mainly in the quasi-static approximation) to point out several aspects of the rich mechanical response of constitutive theories in implicit form. [ABSTRACT FROM AUTHOR]