Blood-pool MRI contrast agents: Properties and characterization

Unlike extracellular MRI contrast agents, which distribute non-specifically throughout the plasma and interstitial space of the body, blood-pool contrast agents (BPCA's) can remain largely in the vasculature throughout the period of an MRI examination. Vascular retention is achieved by the larger size of BPCA's, which also affects clearance times, rotational motion, and overall relaxivity. Nuclear magnetic relaxation dispersion (NMRD), NMR, and EPR techniques can provide details of BPCA behavior. Several different approaches for effective BPCA's currently are being developed, including polymeric and dendrimeric complexes of Gd3+, low molecular weight Gd3+ complexes that reversibly bind to serum proteins, and ultra-small iron oxide particles. Applications of blood-pool agents include arterial phase and equilibrium phase MR angiography.