Relaxivities of different superparamagnetic particles for application in NMR tomography

The development of nuclear magnetic resonance (NMR) imaging technique as a clinical diagnostic modality has prompted the need for a new class of pharmaceuticals, so-called margneto-pharmaceuticals. These drugs must be administered to a patient in order to (1) enhance the image contrast between normal and diseased tissue and/or (2) indicate the status of organ functions or blood flow. A number of different agents have been suggested as potential NMR contrast agents, most of which is highly paramagnetic. Superparamagnetic particles represent an alternative class of NMR contrast agents that usually referred to as T-2 or T-2* contrast agents, opposed to T-1 agents such as paramagnetic chelates. Because of their large permanent dipole moments these agents are able to relax neighbouring nuclei faster than paramagnetic ions. The synthesis and measurements of the transverse R-2 and longitudinal R-1 relaxivities of some ferro-, ferri- and superparamagnetic particles' suspensions are presented. (C) 1999 Elsevier Science B.V. All rights reserved.