MRI of cells and mice at 1 and 7 Tesla with Gd-targeting agents: when the low field is better!

Tumor cells were targeted with Gd-loaded/LDL (low density lipoproteins) adducts consisting of ca 300Gd(III) amphiphilic complexes incorporated in the lipophilic LDL particles. The long reorientational time of the Gd(III) complex in the supramolecular adduct yielded a relaxivity peak at ca 1T, whereas its relaxivity at 7T was 5 times less. The field-dependent relaxivity markedly affected the signal enhancement attainable at the two magnetic fields. As tumor cells showed up-regulation of LDL transporters, B16 melanoma cells were labeled with the Gd-loaded/LDL adduct. Each cell contained ca 2×10 9 Gd atoms. Upon dispersion of 5000 labeled cells in 1μl of agar, signal intensity (SI) enhancements of about 30 and 7% were observed at 1 and 7T, respectively. The results obtained on cellular systems were confirmed in vivo upon the administration of Gd-loaded/LDL particles to C57 mice bearing a transplanted melanoma (B16) tumor. From the herein reported results, one may conclude that, for slowly moving Gd complexes, it is possible to obtain in vivo sensitivity enhancements at 1T several times higher than that attained at high fields. Copyright © 2011 John Wiley & Sons, Ltd. A comparison between the efficiency of slowly moving macromolecular MRI imaging probes at 1 and 7Tesla was carried out using Gd-loaded/LDL (Low Density Lipoproteins) adducts consisting of 250Gd amphiphilic complexes incorporated in the lipophilic LDL particles. The sensitivity enhancement obtained at 1Tesla of B16 melanoma cells labeled with Gd-AAZTAC17/LDL adduct is several times higher than that attained at higher fields.