CEST Imaging Techniques & Challenges
Gil Navon1

1School of Chemistry, Tel Aviv University, Tel Aviv, Israel

Synopsis

The following applications of CEST-MRI for endogenous and exogenous diamagnetic agents will be reviewed: glycoCEST, gagCEST, gluCEST, APT, crCEST, miCEST, sialoCEST and mucCEST, glucoCEST and acidoCEST.

Abstract

The idea of chemical exchange saturation transfer (CEST) as a method to detect small concentrations of metabolites, based on magnetization exchange between exchangeable protons and water, was first suggested by Balaban and co-workers 16 years ago [1]. Selective long CW irradiation on the exchangeable protons on the metabolites causes their saturation, and the magnetization flowing from the water protons by chemical exchange causing reduction in the water peak. Thus, millimolar concentrations of metabolites induce changes in the much larger water proton pool (about 110 molar). Recently this idea started be used for imaging with multitude of applications.

CEST agents can be divided into the following classes: diamagnetic CEST (diaCEST), paramagnetic CEST (paraCEST), and hyperpolarized CEST (hyperCEST). In the talk examples will be given for the diaCEST. A number of excellent reviews have been written on the CEST method and applications [2-7]. diaCEST can be further divided into the classes of endogenous and exogenous agents. Lee et al give a survey of the in vitro CEST properties of endogenous CEST agents that are commonly found in biological tissues and organs at 3T and 7T and at various pH values [8].

Examples of applications of endogenous agents are: glycoCEST for the detection glycogen, the primary storage form of glucose in mammalian tissues [9]; gagCEST for the glycosaminoglycans detection in cartilage and in intervertebral discs [10-13]; gluCEST for detection of glutamate, which is the major excitatory neurotransmitter in the brain and its applications for Alzheimer's disease and epilepsy [14-20]; Amide Proton Transfer (APT) based on proton exchange from amide NH groups from proteins [21,22]; crCEST, for creatine in muscle tissues [23-27]; miCEST: Myo-inositol is a marker of glial cells proliferation. Its concentration is altered in many brain disorderes and has been shown to increase in early Alzheimer’s disease (AD) pathology [28-29]; sialoCEST and mucCEST: Sialic acid (SA) residues are attached to cell-surfaces and proteins as in glycoproteins, and peptides as in mucopolysaccharides. The mammalian central nervous system has the highest concentration of SA, most of which is present in gangliosides and glycoproteins. Mucins are highly glycosylated proteins containing SA residues that are over-expressed in many types of tumors and are associated with their malignancy [30-31].

Examples of exogenous agents: glucoCEST: The property of cancer cells to preferentially absorb glucose is known as the Warburg Effect. Enhanced CEST-MRI of tumors was reported following administration of glucose and of its analogues 2-deoxy-D-glucose, 2-fluoro-2-deoxy-D-glucose, and of 3-O-methyl-D-glucose [32-36]; acidoCEST: In addition to tissue pH measurements using endogenous agents such as APT of proteins [ 21], gluCEST of glutamate [19, 21] and crCEST of creatine [27], the use of exogenous agents was developed for the determination of extra-cellular pH [37-45].

Acknowledgements

No acknowledgement found.

References

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Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)