Proton Relaxation Caused by Magnetic Resonance Imaging Contrast Agent, Oral Magnetic Particles.

Abstract

Physicochemical properties of a newly developed oral negative contrast agent, oral magnetic particles (OMP, Ferristene), for abdominal magnetic resonance (MR) imaging were evaluated in a preformulation study. X-Ray diffiraction pattern and transmission electron micrograph showed that a fine ferrite of iron oxide (diameter less than 30 nm) is absorbed onto the latex particles (approximately 3.5 μm). The longitudinal proton relaxation of an aqueous system containing OMP proceeded mono-exponentially. The transverse proton relaxation, which was much faster than the longitudinal one, proceeded multi-exponentially, where initial fast decay within first echo followed by bi- or mono-exponential decay was observed. This initial fast decay was characterized as percentage of initial magnetic loss (%IML), which increased with increase in OPM concentration, echo time (TE), or both.The %IML is believed to be a result of water protons which diffiuse through strong magnetic field gradient close to the OMP causing them to lose phase coherence of spins prior to the first echo. For the practical use of spin echo sequence in a clinical MR imaging system (TEg10 ms), the OMP concentration around 100 μg Fe/ml for oral suspension seemed preferable for suppression of the signal intensity from the gastrointestinal tract.