Lanthanide-EDTA doped agarose gels for use in NMR imaging phantoms

Gadolinium-ethylene-diamine-tetraacetic acid (Gd-EDTA) doped agarose gels have been used extensively to produce magnetic resonance imaging test materials. These materials are limited in their use in imagers operating at different frequencies and temperatures. The aim of this paper is to show that the theories used to predict the relaxation times for Gd-EDTA doped gels could be used for other paramagnetic lanthanide-EDTA gels with the aim of producing materials whose relaxation times can be theoretically determined but are less temperature and frequency dependent. In the present work, various lanthanide-EDTA gels were studied regarding their NMR T1 and T2 water proton relaxation time dependencies with temperature and proton Larmor frequency. Gd-EDTA doped agarose gels have a T1 relaxation time dependence with temperature of 7.5 ms/K. However an Er-EDTA doped gel has a temperature dependence of only 3.2 ms/K. Similarly Gd-EDTA doped agarose gels vary by 3.48 ms/MHz over the frequency range 2.5 MHz to 80 MHz compared to Ho-EDTA, which varies 0.359 ms/MHz over the same range. These results show that it is possible to produce lanthanide-EDTA doped agarose gels that have markedly reduced temperature and frequency dependences of their relaxation times, but are still predictable using existing theories. This would allow the direct comparison of the performance of imagers operating at different frequencies and temperatures.