Molecular and functional imaging of cancer: advances in MRI and MRS.

Publisher Summary This chapter presents an overview of the endogenous and exogenous magnetic resonance (MR) contrast mechanisms utilized in characterizing tumor vasculature. Every contrast mechanism for probing the tumor vasculature, including the use of exogenous MR contrast agents, is in some way a result of the changes in the MR signal intensity brought about by changes in tissue relaxation times. Noninvasive multinuclear magnetic resonance imaging (MRI) and MR spectroscopic imaging (MRSI) provide a wealth of spatial and temporal information on tumor vasculature, metabolism, and physiology. The most commonly used MR contrast agents (CA) are paramagnetic gadolinium chelates. These agents are tightly bound complexes of the rare earth element gadolinium and various chelating agents. A simple linear compartment model, describing uptake of the contrast agent from plasma, postulates a negligible reflux of the contrast agent from the interstitium back to the blood compartment. Blood concentrations of the CA can be approximated to be constant for the duration of the MR experiment, and under these conditions, contrast uptake is a linear function of time. The MR detection of cellular targets is also elaborated.