A DTPA-Gd containing polymer was grown in the interior of a heat shock protein cage resulting in T1 particle relaxivities of 4,200mM-1 sec-1 for the 12nm particle. Relaxivity parameters were determined and this analysis suggests that the rotational correlation time has been optimized while the water exchange life time is slower than optimal. This synthetic approach holds much promise for the development of next generation contrast agents and this report will aid in their design.