Application of Chemical Exchange Saturation Transfer (CEST) in neuroimaging

Since the early eighties MRI has become the most powerful technic for in-vivo imaging particularly in the field of brain research. This non-invasive method allows acute anatomical observations of the living brain similar to post-mortem dissected tissues. However, one of the main limitation of MRI is that it does not make possible the neurochemical identification of the tissues conversely to positron emission tomography scanner which can provide a specific molecular characterization of tissue, in spite of poor anatomical definition. To gain neurochemical information using MRI, new categories of contrast agents were developed from the beginning of the 2000's, particularly using the chemical-exchange saturation transfer (CEST) method. This method induces a significant change in the magnitude of the water proton signal and allows the detection of specific molecules within the tissues like sugars, amino acids, transmitters, and nucleosides. This short review presents several CEST contrast agents and their recent developments for in vivo detection of metabolites and neurotransmitters in the brain for research and clinical purposes.