[Optimization of dosage and exam technique in the use of oral contrast media in magnetic resonance].

Aim of our study was to optimize the dose, scan delay and sequences for use in MR studies with an oral contrast agent (FerriSeltz, Bracco, Milan, Italy) to obtain positive or negative contrast enhancement in the bowel lumen. MATERIAL AND METHODS: In vitro: 10 mL vials with increasing concentrations (10-100 mg/mL) of the agent, containing 200 mg ferric ammonium citrate/g, were studied with a 1.5 T magnet (Philips NT, The Netherlands), by acquiring T2-weighted STIR and TSE and T1-weighted TFE sequences. Signal intensity was compared by using a ROI. In vivo: 16 volunteers were examined with the same sequences at 20 minutes and 2 hours after the oral administration of 6-27 g of the product diluted in 600 mL water. Images were analyzed by two radiologists and scored on a 4-point scale based on signal intensity; results were compared with Student's "t"-test. RESULTS: In vitro: MR signal was always hyperintense on T1-weighted images, as well as on T2-weighted TSE and SPIR images at concentrations lower than 45 mg/mL. Hypointense signal was seen on T2-weighted TSE and SPIR images at higher concentrations and on STIR sequences at 10-20 mg/mL concentrations. In vivo: the bowel exhibited positive enhancement on T1-weighted TFE and T2-weighted TSE and SPIR images 20 minutes after contrast agent administration at concentrations lower than 45 mg/mL. At 2 hours, bowel loops were hypointense on T2-weighted TSE and SPIR images at 15-20 mg/mL concentrations. STIR images showed hypointense bowel loops at both 20 minutes and 2 hours after 10-20 mg/mL contrast agent administration. Quantitative analysis showed a statistically significant superiority (p < .05) of T2-weighted STIR images in providing negative opacification of the bowel lumen. CONCLUSIONS: Ferric ammonium citrate, being a positive or negative contrast agent according to its dilution, permits to tailor the dose to optimize bowel lumen opacification.