Proton relaxation caused by magnetic resonance imaging contrast agent, oral magnetic particles

Physicochemical properties of a newly developed oral negative contrast agen t, oral magnetic particles (OMP, Ferristene), for abdominal magnetic resona nce (MR) imaging were evaluated in a preformulation study. X-Ray diffractio n pattern and transmission electron micrograph showed that a fine ferrite o f iron oxide (diameter less than 30 nm) is absorbed onto the lates particle s (approximately 3.5 mu m). The longitudinal proton relaxation of an aqueou s system containing GRIP proceeded mono-exponentially. The transverse proto n relaxation, which was much faster than the longitudinal one, proceeded mu lti-exponentially, where initial fast decay within first echo followed by b i- or mono-exponential decay was observed. This initial fast decay was char acterized as percentage of initial magnetic loss (%IML), which increased wi th increase in OMP concentration, echo time (TE), or both. The %IML is beli eved to be a result of water protons which diffuse through strong magnetic field gradient close to the OMP causing them to lose phase coherence of spi ns prior to the first echo. For the practical use of spin echo sequence in a clinical MR imaging system (TE greater than or equal to 10 ms), the OMP c oncentration around 100 mu g Fe/ml for oral suspension seemed preferable fo r suppression of the signal intensity from the gastrointestinal tract.