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 MRI 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 MR principles underlying CEST and similarities to and differences with conventional magnetization transfer contrast (MTC). In CEST MRI, transfer of magnetization is studied in mobile compounds instead of semisolids. Similar to MTC, CEST has contributions of both chemical exchange and dipolar cross-relaxation, but the latter can often be neglected if exchange is fast. Contrary to MTC, CEST imaging requires sufficiently slow exchange on the MR 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.

Assessment of Mechanical Properties of Muscles from Multi-Parametric Magnetic Resonance Imaging

“…Moreover, the high sensitivity of T1ρ to cartilage or intervertebral disc degeneration has been demonstrated [19] [22]. Chemical exchange saturation transfer (CEST) agents provide a powerful source for potential contrast including pH imaging, metabolite detection, imaging of mobile proteins or peptides in tissue, metal ion detection, liposome labeling, nanoparticle/polymer labeling, protein-binding, RNA or DNA-protein binding, temperature imaging, detecting enzyme activity, and imaging of OH groups, polyamines, and nucleic acids [42]. However, CEST was not applied yet to the musculoskeletal muscle.…”

Amide Proton Transfer Imaging in Clinics: Basic Concepts and Current and Future Use in Brain Tumors and Stroke

“…The water longitudinal relaxation time (T1w) and water proton concentration can affect the APT signal (2,7,8). With respect to (12,13).…”

Temperature dependence of 1H NMR chemical shifts and its influence on estimated metabolite concentrations

“…This signal enhancement technique allows the indirect detection of endogenous or exogenous molecules with exchangeable protons of amide, amine, or hydroxyl groups (for reviews see [22,23]). Since the size of the observed CEST effect depends on the pool sizes (water, metabolites), an accurate metabolite quantification is of central importance.…”