Tissue distribution and magnetic resonance spin lattice relaxation effects of gadolinium-DTPA.

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Abstract
Gadolinium-DTPA [diethylenetriaminepentaacetic acid] complex (Gd-DTPA) is a potential clinical magnetic resonance (MR) contrast agent that enhances images primarily by decreasing spin-lattice relaxation time (T1) in tissues in which it localizes. This study was designed to determine the immediate tissue distribution of i.v. administered Gd-DTPA in selected organs of interest as a function of administered dose and tissue Gd-DTPA concentration. An i.v. bolus of Gd-DTPA with a tracer quantity of Gd-153 was administered to 3 groups of rabbits at the following doses: 0.01 mM/kg (n = 6); 0.05 mM/kg (n = 6); 010 mM/kg (n = 6). A control group received sham injections. Five min after Gd-DTPA was administered, all animals were killed; samples of serum, lung, heart, kidney, liver and spleen were analyzed in a 0.25 T MR spectrometer to measure T1, and then in a .gamma. well counter to determine tissue concentration of Gd-DTPA. Tissue distribution (% dose/tissue wt in g) at 5 min after injection was proportionally constant over the range of doses given. Tissue concentration varied linearly with injected dose (r > 0.98 for all tissues). Relaxation rate (1/T1) varied linearly with injected dose and with tissue Gd-DTPA concentration (r > 0.97 for all tissues). The order of tissue relaxation rate response to a given dose was kidney > serum > lung > heart > liver > spleen. Because of its extracellular distribution and linear relaxation rate vs. concentration relationship, Gd-DPTA enhancement in MR images may be a good marker of relative organ perfusion.