J Korean Soc Magn Reson Med.  2000 Jun;4(1):27-33.

Determination of Electron Spin Relaxation Time of the Gadolinium-Chealted MRI Contrast Agents by Using an X-band EPR Technique

• Hong SW
• Chang Y
• Hwang MJ
• Rhee IS
• Kang DS

Abstract

PURPOSE
To determine the electronic spin relaxation times, T1e, of three commercially available Gd-chelated MR contrast agents, Gd-DTPA, Gd-DTPA-BMA and Gd-DOTA, using Electron Paramagnetic Resonance(EPR) technique. Material and Methods: The paramagnetic MR contrast agents, Gd-DTPA(Magnevist), Gd-DTPA-BMA(OMNISCAN) and Gd-DOTA(Dotarem), were used for this study. The EPR spectra of these contrast agents, which were prepared 2:1 methanol/water solution, were obtained at low temperatures, from-160degrees C~-20degrees C. The glassy-state EPR spectra for these contrast agents were then fitted by the simulation spectra generated with different zero-field splitting (ZFS) parameters by a computer simulation program 'GE N', which generates the EPR powder spectrum using a given ZFS in 3X3 tensor. Finally, the spin relaxation times of the contrast agents were then determined from the T2e, D, and E values of the best simulation spectra using the McLachlan's theory of average relaxation rate.
Results
The electronic transverse spin relaxation times, T2e's, of Gd-DTPA, Gd-DTPA-BMA and Gd-DOTA were 0.113ns, 0.147ns and 1.81ns respectively. The g-values were 1.9737, 1.9735 and 1.9830 and the electronic spin relaxation times, T1e's, were 18.70ns, 33.40ns and 1.66micros, respectively.
Conclusion
The results of these studies reconfirm that the paramagnetic MR contrast agents with larger ZFS parameters should have shorter T1e's. Among three contrast agents used for this study, Gd-DOTA chelated with cyclic ligand structure shows better electronic property then the others with linear structure. Thus, it is concluded that the exact determination of ZFS parameters is the important factor in evaluating relaxation enhancement effect of the agents and in developing new contrast agents.

MeSH Terms

Computer Simulation
Contrast Media*
Gadolinium DTPA
Magnetic Resonance Imaging*
Relaxation*
Contrast Media
Gadolinium DTPA