ABSTRACT
The contrast in chemical-exchange saturation transfer (CEST) MRI originates from chemical exchange between labile protons and water protons. Imaging is obtained by saturating the proton pool of interest and allowing magnetisation to be transferred between it and the larger solvent pool. In vivo, this effect can be used to measure the concentration of both endogenous and exogenous agents. The full CEST experiment requires the collection of a full z-spectrum, sweeping a range of offsets on both sides of the water frequency. Several methods can be implemented to speed up the acquisition. Once the centre of the z-spectrum representing the water resonance frequency is determined, the magnitude of the CEST effect can be quantified as MT asymmetry ratio, that is, by comparing the amplitude of the spectrum at offsets ∆ω and -∆ω. This approach suffers from a series of potential biases, which have led to the development of model-based approaches that allow separation of the contributions from various metabolites in a more systematic way. Absolute quantifications of the CEST effect are also possible, and some of the techniques available are reviewed in this chapter. The chapter also reviews the currently available CEST agents and the main applications of the technique.
