ABSTRACT
Magnetic resonance imaging (MRI) is a versatile technology that
employs water content and water relaxation properties to image
the anatomy and physiology of the body. Currently, MRI has
been widely used in hospitals for the localization, diagnosis, and
characterization of cancer [1, 2], stroke [3], and other diseases,
and for the assessment of treatment effects. In addition to the
conventional MRI sequences, such as T1-weighted (T1w) and T2weighted (T2w), several advanced, functional MRI techniques [4, 5], such as perfusion imaging, diffusion imaging, and proton MR
spectroscopic imaging, have been emerging in clinical research
protocols. As MRI is applied further at the molecular level, more
possibilities for disease diagnosis and treatment assessment will
become evident [6, 7]. Currently, most molecular and cellular
MRI studies rely on the administration of paramagnetic or super-
paramagnetic metal-based substrates that are potentially harmful.
Ideally, molecular imagingwould exploit endogenousmolecules that
can be probed non-invasively using existing hardware. Pioneered by
Balaban et al. [8-10], chemical exchange saturation transfer (CEST)
imaging is a new molecular MRI method that allows detection
of low-concentration, endogenous or exogenous chemicals with
exchangeable protons through the water signal [11-13]. In the
past several years, many new CEST contrast agents have been
designed-diamagnetic [14], paramagnetic (paraCEST) [15, 16], and
even hyperpolarized (hyperCEST) [17]—and the validation of new
types of applications is progressing rapidly on many fronts.
