Imaging Biomarkers of Angiogenesis and the Microvascular Environment in Cerebral Tumors

The structure and organization of blood vessels within tumor tissue is very different from that seen in normal tissues. Tumor blood vessels show abnormalities in microstructure and hierarchical organization, which result from multiple factors including local tumor characteristics, angiogenic drive, and the ability of the angiogenic process to keep pace with tumor growth. Tumor microvasculature is inefficient compared to that seen in normal tissues, and, particularly in rapidly growing tumors, blood flow is often inadequate to meet the demands for oxygen and nutrient delivery and clearance of waste material. Understanding the microvascular environment and its variation between and within tumors is critical for an understanding of tumor behavior and therapeutic response. A wide range of quantitative imaging techniques have been developed in an attempt to provide noninvasive, repeatable assays of microvascular characteristics which can then be studied in terms of their spatial variability and change over time. This chapter reviews the currently available imaging biomarkers and their current clinical application.