Chemical Exchange Saturation Transfer Imaging

Chemical exchange saturation transfer (CEST) imaging can provide information from metabolites, lipids and proteins, which are not directly detectable with conventional MRI sequences due to their low concentration in tissue. CEST employs a frequency-selective radio-frequency saturation to saturate magnetization of protons from the solute pool. CEST contrast originates from the chemical exchange of labile protons from solutes with those from water molecules. Saturation of the solute pool results in a detectable signal attenuation of the water pool depending on the exchange rate and the solute concentration. This effect can be used to indirectly observe changes in metabolite concentration or protein content, as well as in tissue parameters such as intracellular pH. Compared to MR spectroscopy, CEST can provide localized images with higher spatial resolution. This makes CEST very advantageous for clinical applications.

Recent CEST studies using 7 Tesla scanners have shown an increased CEST effect and higher spectral resolution of the CEST signal at ultrahigh field. However, CEST imaging at ultrahigh field is very challenging due to the detrimental effect of B0 and B1 inhomogeneity, long acquisition duration and the limited coverage of the standard CEST sequences, B1 power and T1 dependence of CEST, and magnetization transfer effects that contribute to the CEST signal. Therefore, further technical developments on CEST acquisition and analysis schemes are needed to conduct clinical research studies using CEST on 7 Tesla scanners. This project aims to address challenges associated with CEST imaging at ultrahigh field and to obtain robust and reliable CEST signal from the human brain in vivo.