title: Chemical exchange saturation transfer (CEST): what is in a name and what isn't?
abstract: Chemical exchange saturation transfer (CEST) imaging is a relatively new magnetic resonance imaging contrast approach in which exogenous or endogenous compounds containing either exchangeable protons or exchangeable molecules are selectively saturated and after transfer of this saturation, detected indirectly through the water signal with enhanced sensitivity. The focus of this review is on basic magnetic resonance principles underlying CEST and similarities to and differences with conventional magnetization transfer contrast. In CEST magnetic resonance imaging, transfer of magnetization is studied in mobile compounds instead of semisolids. Similar to magnetization transfer contrast, CEST has contributions of both chemical exchange and dipolar cross-relaxation, but the latter can often be neglected if exchange is fast. Contrary to magnetization transfer contrast, CEST imaging requires sufficiently slow exchange on the magnetic resonance time scale to allow selective irradiation of the protons of interest. As a consequence, magnetic labeling is not limited to radio-frequency saturation but can be expanded with slower frequency-selective approaches such as inversion, gradient dephasing and frequency labeling. The basic theory, design criteria, and experimental issues for exchange transfer imaging are discussed. A new classification for CEST agents based on exchange type is proposed. The potential of this young field is discussed, especially with respect to in vivo application and translation to humans.
authors.affiliation: The Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA. pvanzijl@mri.jhu.edu
authors.forename: Peter C M
authors.initials: PC
authors.lastname: van Zijl
authors.forename: Nirbhay N
authors.initials: NN
authors.lastname: Yadav
mesh_terms: D000465:Algorithms; D000818:Animals; D003198:Computer Simulation; D003287:Contrast Media; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008954:Models, Biological; D011522:Protons
chemical_list: D003287:Contrast Media; D011522:Protons