AI Article Synopsis
- The study investigates how different factors influence the longitudinal relaxivity (r) of two commercial MRI contrast agents, Gd-DOTA and Gd-HP-DO3A, and introduces a new compound, Gd-Phen-DO3A, designed for better performance.
- It measures the longitudinal relaxation rates of these agents in various solutions, including saline and human plasma, to identify the key elements affecting their relaxivity values.
- Findings show that relaxivity improves in more viscous environments and with protein interactions, with Gd-Phen-DO3A demonstrating the highest increase in plasma, emphasizing the importance of viscosity, complex-protein interactions, and pH on the relaxivity of these agents.
Article Abstract
Purpose: To dissect the contributions to the longitudinal relaxivity (r ) of two commercial contrast agents (CAs), Gd-DOTA and Gd-HP-DO3A, and to synthesize/characterize a novel macrocyclic agent (Gd-Phen-DO3A) having superior r .
Methods: Longitudinal relaxation rates R of the CAs in saline with/without human serum albumin (HSA), ionized simulated body fluid (i-SBF), viscous simulated body fluid (v-SBF), and human plasma were measured. Results have been interpreted to evince the main determinants to the observed r values.
Results: In v-SBF or in the presence of HSA, r is enhanced for all complexes, reflecting the viscosity increase and a weak interaction with proteins. The CAs further differentiate in plasma, with a relaxivity increase (versus saline) of approximately 1, 1.5, and 2.5 mM s for Gd-DOTA, Gd-HPDO3A, and Gd-Phen-DO3A, respectively. R versus pH curves in i-SBF indicates that prototropic exchange sizably contributes to the relaxivity of Gd-HP-DO3A and Gd-Phen-DO3A.
Conclusion: The major contributions to r in the physiological environment have been highlighted, namely, increased viscosity, complex-protein interaction, and prototropic exchange. The control of these terms allows the design of novel macrocyclic structures with enhanced r as a result of an improved interaction with plasma's macromolecules and the shift of the prototropic exchange to physiological pH. Magn Reson Med 78:1523-1532, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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