CT and MR to assess the response of liver tumors to hepatic perfusion

Assessment of the response of liver tumors to hepatic perfusion is strongly based on cross-sectional imaging. CT and MRI have gained considerably in diagnostic accuracy with the introduction of new, fast acquisition techniques such as spiral CT or breath-hold techniques in MRI. In addition, the administration of contrast agents has improved and has led to new injection protocols in spiral CT and the development of liver-specific contrast agents in MRI. Imaging techniques, however, strongly rely on changes in morphology such as size, vascularization and signs of necrosis. Functional signs of tumor metabolism cannot be visualized directly. While most functional imaging techniques at present are based on nuclear medicine, MR spectroscopy (MRS) offers the potential to assess tumor metabolism. Its promise is a direct match between the morphologic information of MRI and the metabolic information provided by MRS. The application of MRS to the liver, however, is still in this infancy. This article will give an overview of the multitude of CT and MR techniques that can be used to monitor tumor response. It will discuss the various signs of tumor regression and some typical complications of hepatic perfusion therapy. In particular, the influence of tumor characteristics-tics on the optimum choice of imaging technique will be demonstrated.