Proton relaxation enhancement of albumin, immunoglobulin g, and fibrinogen labeled with gd‐dtpa

Abstract
Bovine serum albumin, immunoglobulin G, and fibrinogen were labeled with Gd‐DTPA using a bifunctional chelating agent DTPA anhydride. The protein‐(Gd‐DTPA) conjugates had 1.4‐ to 2.0‐fold greater longitudinal relaxivities at 0.02 and 0.44 T than the relaxivity of plain Gd‐DTPA. The increase of longitudinal relaxivity was not directly related to the size of carrier protein. Up to 50 Gd‐DTPA chelates per protein, longitudinal relaxivity of the conjugates was proportional to the concentration of Gd and independent of the Gd/protein ratio.