The effects of paramagnetic contrast agents on metabolite protons in aqueous solution

The longitudinal (R1) and transverse (R2) relaxivities of the clinically used contrast agents Gd(DTPA)2-, Gd(DOTA)- and Gd(DTPA-BMA) have been determined in mixed aqueous metabolite solutions for choline, creatine and N-acetylaspartate. Measurements were performed at 1.5 T using a STEAM sequence on 25 mM metabolite solutions at pH = 7.4 and 22 degrees C. The data showed that for all the contrast agents and metabolites, R1 approximately = R2. The largest range of relaxivity values was found for Gd(DTPA)2-, where R2 = 6.8 +/- 0.3 mM(-1) s(-1) for choline and 1.5 +/- 0.4 mM(-1) s(-1) for N-acetylaspartate. Variation in relaxivity values was attributed primarily to differences between the charges of the paramagnetic agent and metabolite. The maximum potential influence of the contrast agents on in vivo metabolite signals was calculated using the measured relaxivities.