ABSTRACT
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.
