MR-Derived Biomarkers for Cancer Characterization

Abstract

Magnetic resonance (MR) can be exploited in a variety of ways to obtain a wide range of anatomical and physiological information in a safe and noninvasive manner. This makes MR imaging (MRI) and spectroscopy (MRS) valuable tools in cancer research and clinical oncology, among other fields. This chapter provides a basic introduction to MR physics and describes how different in vivo MR techniques are used to noninvasively characterize tumors and the tumor microenvironment. Two of the most commonly utilized techniques are contrast-enhanced MRI and diffusion-weighted MRI. Contrast-enhanced MRI methods are used to evaluate tumor vascularization and vascular function by measuring the kinetics and distribution of intravenously administered contrast agents. Diffusion-weighted MRI is sensitive to the diffusion of water molecules in the tissue, from which inferences about tumor cellularity and tissue microstructure can be made. Blood-oxygen-level-dependent MRI can distinguish between oxygenated and deoxygenated blood as a proxy to tumor oxygenation. In addition, efforts have been made to develop targeted contrast agents to directly image hypoxia. MRS can be used to measure the levels of various metabolites such as lactate and choline that are involved in metabolic reprogramming in cancer. Both endogenous and exogenous pH-sensitive indicators enable spectroscopic measurement of tumor pH. While this chapter does not provide an exhaustive overview of the MR methods used for cancer characterization, it discusses both clinical and experimental techniques that highlight the versatility of MR as a tool for exploring some key aspects of the tumor microenvironment.