PARACEST Agent Characteristics

A novel PARACEST contrast agent (Eu³⁺-DOTAM-Gly-Phe) was evaluated as a potential temperature imaging agent at 9.4T under conditions of physiologic pH. This contrast agent was found to have significantly greater saturation transfer between the bound water and bulk water pools (CEST effect) compared to Eu³⁺-DOTAM-Gly for temperatures between 32–50°C (including the physiologic range) when controlling all other experimental conditions and using low (14 μT) saturation power.

Molecular structure of Eu3+ chelates with ligands DOTAM-Gly and DOTAM-Gly-Phe and bound water.

Temperature maps produced in phantom A containing an aqueous solution of 10 mM Eu3+-DOTAM-Gly-Phe (a), phantom B containing 5% BSA and 15 mM Eu3+-DOTAM-Gly-Phe (b), and phantom C containing brain tissue with 4 mM Eu3+-DOTAM-Gly-Phe (c). The temperature measured by a fiber optic temperature sensor placed adjacent to each phantom was 37.5°C. The corresponding average CEST spectra and the average asymmetry curves are displayed above the temperature maps.