One of the most attractive features of chemical exchange saturation

transfer (CEST) imaging is its ability to detect naturally occurring

compounds that are part of important metabolic pathways using

labile protons already present on these compounds, allowing direct

molecular imaging studies. This is a unique feature for magnetic

resonance imaging (MRI) contrast agents, as paramagnetic and

superparamagnetic MRI contrast agents instead require conjugation

or association of metals to these compounds to impart signal

contrast, which is less desirable. Furthermore, while conventional

proton magnetic resonance spectroscopy (1H MRS) and magnetic

resonance spectroscopic imaging (MRSI) also allow the detection

and quantification of metabolites, these techniques have always

been limited by their relatively low sensitivity, and as such images

produced using these techniques suffer from low spatial resolution

in vivo. In addition, hyperpolarization has allowed the detection

of organic compounds such as isotopically labeled pyruvate and

lactate. However, this technique currently has challenges in imag-

ing for more than several minutes after the administration of

hyperpolarized substrate in live subjects due to T1 relaxation of hyperpolarized spins. This combination of factors has led to a

great enthusiasm for developing CEST imaging technologies for the

amplified detection of a variety of organic compounds.