Kinetics of a novel blood pool agent (MP-2269) with persistent high relaxivity for MR angiography.

Significant improvements in MR angiography (MRA) are obtained when the T1 value of blood is shortened using an MR contrast agent (1). Current, clinically approved agents are not confined to the intravascular space due to their small molecule size, and therefore, in most applications, show only a significant improvement in MRA during the first pass of the agent. This small acquisition-time window requires very fast MR acquisition techniques, thereby limiting the clinical application. Some applications like coronary artery angiography are not feasible in such a short acquisition window with current MR techniques due to inherently low gating efficiency. Therefore, the availability of blood-pool agents with a relatively longer blood half-life would be a significant advantage for both MR coronary angiography and other MR angiography applications. Initially, large molecular agents were proposed as blood-pool agents (2,3). However with large molecular agents, body clearance becomes a limiting factor in human use. While faster body clearance is obtained with smaller molecular agents, they are not confined to the intravascular space as well as large molecular agents. One solution to the dilemma of molecular size is an agent which binds reversibly to a blood macromolecule in vivo (4,5). A new