Preliminary evaluation of iron phytate (inositol hexaphosphate) as a gastrointestinal MR contrast agent

A simple, effective, safe, and well-tolerated contrast agent is needed as a bowel marker for magnetic resonance (MR) imaging. The authors tested a variety of foodstuffs admixed with ferric iron as potential gastrointestinal MR contrast agents. Phytate (inositol hexaphosphate) more than doubled the relaxivity of solutions of ferric iron. Because of the improved relaxivity of iron phytate, the concentration of iron could be reduced substantially relative to free ferric iron (eg, ferric chloride or ferric ammonium citrate). Imaging studies were performed in five volunteers to determine the optimal dose of iron phytate and in five additional volunteers to test its effectiveness. A 200 mg/L concentration of ferric iron with phytate functions as an effective gastrointestinal MR contrast agent for T1-weighted abdominal MR imaging, significantly improving bowel contrast (P < .01). Blood studies after contrast agent administration showed no appreciable increase in serum iron. Compared with standard chelate complexes that decrease the relaxivity of a given paramagnetic ion, phytate not only decreases the absorption of the iron but increases its relaxivity.