Hepatobiliary Magnetic Resonance Contrast Agents Assessed by Gadolinium-153 Scintigraphy

Abstract

A simple method to test new gadolinium complexes potentially useful as enhancement agents for magnetic resonance imaging was developed. Healthy rats underwent scintigraphy with two potential hepatobiliary agents, diethyl IDA and diisopropyl IDA complexed with gadolinium-153. Control products included ¹⁵³Gd DTPA, ¹⁵³GdCl₃ and technetium-99m diethyl IDA. As shown scintigraphically, ¹⁵³Gd IDA complexes were partially excreted by urinary and hepatobiliary excretion early after administration. These findings paralleled significant reduction in ¹H Tl values of excised livers. However, these agents exhibited prolonged ¹⁵³Gd whole-body retention. The prolonged tissue distribution of ¹⁵³Gd activity in animals given ^l53Gd diethyl IDA did not differ significantly from that observed in animals given GdCb, and could be attributed to chemical instability or reticuloendothelial uptake. The scintigraphic method permits screening of gadolinium complexes in animals by showing mass balance, kinetics, distribution, and effective stability. Biologic effects of tracer or pharmacologic levels can be compared with those of carrier-free and carrier-added Pharmaceuticals.