1,4,7,10-Tetraazacyclododecane-1,4,7-triacetic acid, 10-[2-[[2-(2,5-dihydro-2,5-dioxo-1H-pyrrol-1-yl)ethyl]amino]-2-oxoethyl]-, 1,4,7-tris(1,1-dimethylethyl) ester [ 1613382-10-7 ]