Chemical exchange saturation transfer (CEST)

Our current research focuses on developing and optimizing CEST imaging at 3T and 7T, and applying the methodologies for clinical studies with gliomas.

CEST imaging maps the chemical exchange between bulk water protons and exchangeable protons in small metabolites and macromolecules. It provides a new contrast mechanism for studying molecular processes and various properties such as pH, temperature, kinetics and metabolite concentrations.

The exchange process that provides the contrast for CEST imaging can be explained in a simple two-compartment model, where a solute (small metabolites, usually in very small concentrations) protons resonating at a frequency different from the larger pool (bulk water) are engaged in the chemical exchange process. When RF irradiation (saturation) is done at the solute frequency, the saturation is transferred to bulk water via chemical exchange, which can be observed as the changes in the signal intensity of bulk water.

The most commonly studied signals in CEST imaging arise from amide proton transfer signals of peptides and proteins, called amide proton transfer (APT) imaging. The purpose of this study is APT imaging in glioma patients at 7T using whole brain high resolution 3D pulsed CEST imaging method. 

Collage of brain scans
T2w-FLAIR images, amide proton transfer ratio (APTR), MTRasym and f0-shift(ΔB0) maps across seven slices from a tumor subject.
APRR maps were calculated as the mean signal between 3.25 ppm and 3.7 ppm in the difference plot per voxel.
MTRasym maps based on asymmetry analysis of the data across several ppm regions. 
f0-shift(ΔB0) maps calculated based on the location of the minimum in the Lorentzian fit.