Properties of Eu2+ cryptates and their implications to the development of contrast agents for magnetic resonance imaging

• Main Author: Garcia, Joel
• Format: text
• Published: Animo Repository 2022
• Subjects: Europium; Contrast media (Diagnostic imaging); Magnetic resonance imaging; Chemistry
• Online Access: https://animorepository.dlsu.edu.ph/faculty_research/5934
• Institution: De La Salle University

Methods. Physical and imaging properties of a series of cryptands were studied. Biphenyl Eu2+ cryptate was synthesized from biphenyl olefin. Relaxometric measurements using Tesla (T) Siemens Verio and Bruker Clinscan 7 T were performed to determine the efficacy of Eu2+ cryptates at ultra-high field strengths (3 and 7 T). Relaxivity values were calculated from phantom images at 3 and 7 T. The imaging parameters at 3 T resolution = 0.5 x0.5 x 0.5 mm3; echo time (TE) = 5.68 ms; and repetition time (TR) = 37 ms. At 7T, the imagng parameters were resolution = 0.27 x 0.27 x 2.0 mm3; TE = 3.26 ms; and TR = 21 ms. 17O NMR and electron paramagnetic spectroscopic data were used to explain the observed differences in relaxivity values of these cryptates. Results. Small Eu2+ cryptates have higher relaxivity tha a clinically approved contrast agent at ultra-high field strengths. Also an increase in efficiency with increasing field strength was observed for these cryptates. The increase in relaxivity with field strength could be due, in part, to the optimal water-exchange rate at ultra-high field strength and relaxivity high number of inner-sphere water molecules. Surprisingly, a decrease in relaxivity value was obtained when albumin was present in Eu2+ cryptate solutions. 17O NMR data indicates that this decrease in relaxivity could be attributed to the displacement of an inner-sphere water molecule upon albumin binding. Conclusion. Eu2+ cryptates are better contrast agents than the clinically approved Gd3+ DOTA at ultrahigh field strengths (3 and 7 T). Binding to human serum albumin significantly decreased the relaxivity of the biphenyl Eu2+ cryptate due to the displacement of an inner-sphere water molecule.