Five-Site Modeling of Protons Chemical Exchange Processes for in Vivo CEST-Based Molecular Imaging

Julien Flament¹, Benjamin Marty¹, Cline Giraudeau¹, Sbastien Mriaux¹, Julien Valette¹, Christelle Mdina², Caroline Robic², Marc Port², Franck Lethimonnier¹, Gilles Bloch¹, Denis Le Bihan¹, Fawzi Boumezbeur¹

LipoCEST are a new class of contrast agents for CEST-MRI which provide a tremendous amplification factor but suffer from a quite small chemical shift (2-28 ppm) compared to paramagnetic complexes. Consequently, their detection in vivo is hampered by endogenous Magnetization Transfer contrast. It is therefore important to separate specific LipoCEST signal from endogenous background coming from macromolecules. Thus in this study, we propose to characterize water exchange processes using a five-site model by measuring and fitting the Z-spectrum of each tissular compartment of mouse brain in order to achieve quantitative CEST imaging with LipoCEST contrast agents.