Relaxivities of Lanthanide-based MRI Contrast Agents at Low Magnetic Field*

Lanthanide complexes such as Gd-DOTA are widely-used as contrast agents in magnetic resonance imaging (MRI) due to their excellent relaxation properties and chemical stability in vivo. Such MRI contrast agents are optimized at the normal clinical MRI field strengths of 3 T or higher. The recent availability of preclinical MRI scanners operating at low magnetic fields such as 1 T or at earth’s magnetic field requires that these lanthanide-based MRI contrast agents to be optimized at these conditions. In this work, we have characterized the relativities of aqueous solutions of lanthanide complexes at fields of 1 T and at earth’s magnetic field (~0.3 Gauss). In particular, we have measured the concentration dependence of both the proton spin-lattice (T1) and spin-spin (T2) relaxation times of Gd-DOTA and Ho-DOTA solutions. The spin physics and potential applications of these results will be discussed. This study is supported by Welch grant AT-1877, DOD grant W18XWH-17-0303, and CPRIT grant RP180716.