Here we describe two strategies to increase relaxivity at high fields (=3 tesla).  For most Gd(III) complexes, rotational diffusion of the complex governs relaxation of a coordinated water ligand.  To maximize relaxation efficiency, the product of the rotational correlation time and the hydrogen Larmor frequency should be close to 1.  For small metal complexes, this occurs at Larmor frequencies in the gigahertz regime and thus relaxation is not very efficient at fields used for MR imaging.  Alternately, protein- or nanoparticle-bound Gd(III) have long correlation times that can yield very high relaxivity, but only at very low magnetic fields (~0.5 tesla or 20 MHz).Here we describe our recent work with rigid, multimeric, peptide-based complexes to design contrast agents with specific intermediate rotational correlation times to yield high relaxivity at higher magnetic fields.  For protein- or nanoparticle bound Gd(III) complexes with long rotational correlation times, we also describe an alternate strategies to increase relaxivity at high fields.  This involves designing a Gd(III) complex with an extremely fast water exchange rate.  For slow tumbling complexes, it is possible that the water exchange rate can become the limiting rate that governs relaxation.  We will show that albumin-bound complexes with water residency times approaching 1 ns can yield much higher relaxivity at high fields than conventional albumin-bound complexes like MS-325.

Does anybody really know what (correlation) time it is? Designing Gd(III) complexes for high field, high relaxivity applications

247th National Meeting (2014)

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