Optimal pulsing sequences for MR contrast agents.

Chelates of paramagnetic metals have been developed for use as contrast agents for MRI. Several such agents are cleared by biliary excretion and significantly reduce proton T1 and T2 of liver and bile. These influences on proton-relaxation rates also influence the choice of pulsing sequences. In studies on rabbits, with and without contrast agents, the influence of repetition time (TR) and echo-delay time (TE) are demonstrated. Excellent liver images were obtained with an imaging time of 20 sec using TR = 80 msec, TE = 10 msec, and two excitations. The effects of such contrast agents are best imaged at short TR and short TE.