the steric effect and uncertain factors from chemistry synthesis the actual average numbers of metal cations are in general less than the expected numbers for example the actual average numbers of example 2 is 15 6 u00b1 0 2 and the actual average numbers of example 4 is 7 since dendritic polymers with different actual numbers of metal cations have various actual chemical structures the chemical structure with the expected numbers of metal cations was used to generally represent all likely dendritic polymers with actual numbers of metal cations which were prepared from the same synthetic process as shown in table 1 polymers a u02dc d for magnetic resonance imaging mri were developed it consists of paramagnetic gadolinium ions chelated to dtpa benzyl dtpa molecules which in turn were attached to the peripheral of the cyclic dendritic structure the contrast enhancing properties were measured by a 20 mhz nmr spectrometer using a standard inversion recovery pulse sequence to detect the relaxation times in terms of t 1 and t 2 the relaxivities of the dendrimers were found to be much higher than commercial products further the polymer d which had a rigid benzyl linker bridging the dtpa and the dendrimer still exhibited superior relaxivity accordingly the disclosure introduces a concept of dendritic polymer into a design of carriers capable of carrying a plurality of paramagnetic metal cations so as to increase the signal intensity and specific targeting ability of imaging agents per molecule in addition the dendritic molecule recited in the embodiments can avoid developing agents with small.