Stick figure of Gadolinium-DOTA-Dendrimer contrast agent being developed by Dr. Henry Bryant in the Laboratory of Diagnostic Radiology Research.

The three-dimensional representation of a Gadolinium-DOTA-Dendrimer. The 1/T1 and 1/T2 NMR Dispersion (NMRD) profiles show an ion relaxivity increased from 30 mM-1s-1 for the Generation (G) =5 to 35 mM-1s-1 for the G=7 Gadolinium-DOTA-Dendrimer, reaching a plateau at 36 mM-1s 1 for the G=9 and G=10 dendrimers. A similar plateau was observed for 1/T2 with values of 36 mM-1s-1 for G=5, 42 mM-1s-1 for G=7, and 45 mM-1s-1 for the G=9 and G=10 dendrimers. This "saturation" of ion relaxivity for high generation dendrimers occurred over the entire frequency range studied. The 1/T1 and 1/T2 relaxivities decreased as the temperature decreased for each generation of dendrimer studied, implying that slow water exchange of bound water molecules with the bulk solvent limits the relaxivity. These NMRD results suggest that there is an increase in the rotational correlation times associated with higher generations of dendrimer and therefore these large macromolecule do not show significant increases in the ion relaxivity. Although the ion relaxivity does not increase, the total molecular relaxivities increased from 2880 mM-1s-1 to 66960 mM-1s-1 for the G=5 to the G=10 dendrimer.