• The Korean Journal of Nuclear Medicine
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• v.38 no.2
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• pp.205-208
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• 2004

The two major classes of magnetic resonance (MR) contrast agents are paramagnetic contrast agents, usually based on chelates of gadolinium generating T1 positive signal enhancement, and super-paramagnetic contrast agents that use mono- or polycrystalline iron oxide to generate strong T2 negative contrast in MR images. These paramagnetic or super-paramagnetic complexes are used to develop new contrast agents that can target the specific molecular marker of the cells or tan be activated to report on the physiological status or metabolic activity of biological systems. In molecular imaging science, MR imaging has emerged as a leading technique because it provides high-resolution three-dimension maps of the living subject. The future of molecular MR imaging is promising as advancements in hardware, contrast agents, and image acquisition methods coalesce to bring high resolution in vivo imaging to the biochemical sciences and to patient care.

• Journal of the Korean Society of Radiology
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• v.11 no.7
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• pp.589-595
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• 2017

This study evaluated the effect of gadolinium contrast agents on the spectrum of metabolites during $^1H-MRS$ of brain and to investigate whether the contrast agents injected before MR spectroscopy significantly affect the estimated peaks of MRS. From January to May 2017, brain MR spectroscopy was performed on 30 patients to compare the spectrum before and after contrast injection of the brain white matter tissue. As a result, the spectrum of metabolites decreased after the paramagnetic contrast agents injected. However, it was not statistically significant which indicated that the use of contrast agent did not meaningfully affect the spectrum of metabolites. In conclusion, the use of the paramagnetic contrast before the acquisition of the spectroscopy may aid voxel positioning especially when it is difficult to determine the exact location of the lesion or the contrast is low.

• Proceedings of the KSMRM Conference
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• 2000.11a
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• pp.21-21
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• 2000

• Proceedings of the KSMRM Conference
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• 2000.11a
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• pp.68-68
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• 2000

• Proceedings of the KSMRM Conference
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• 2000.11a
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• pp.22-22
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• 2000

• Investigative Magnetic Resonance Imaging
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• v.4 no.1
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• pp.27-33
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• 2000

Purpose: To determine the electronic spin relaxation times, $T_{le}$, 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-DTFA(Magnevist) , Gd-DTFA-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 $-160^{\circ}C~20^{\circ}C$. 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 'GEN', which generates the EPR powder spectrum using a given ZFS in $3{\times}3$ tensor. Finally, the spin relaxation times of the contrast agents were then determined from the $T_{2e}$, 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, $T_{2e}'s$, 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, $T_{1e}'s$, were 18.70ns, 33.40ns and $1.66{\mu}s$, respectively. Conclusion: The results of these studies reconfirm that the paramagnetic MR contrast agents with larger ZFS parameters should have shorter $T_{1e}'s$. 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.

• Proceedings of the KSMRM Conference
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• 2001.11a
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• pp.117-117
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• 2001

목적： 상자성 자기공명 조영제의 효율을 결정하는 중요 인자중의 하나인 조영제의 rotational correlation time ($\tau$R)을 전자상자성공명 data를 측정하고 이를 정량적으로 분석하여 결정하였다. 대상 및 방법： rotational dynamics가 주로 분자의 크기 및 모양에 의해 결정된다는 점을 이용하여 anisotropic한 (equation omitted) tensor를 가지는 VO$^{2＋}$의 VO(DTPA)시료에 대해 다양한 온도에서 즉 다양한 rotational time에 대해 ESR spectrum을 측정하였다. 측정된 EPR data로부터 (equation omitted) 텐서 그리고 최종적으로 $\tau$R 을 SIMPOW와 EPRLF을 사용하여 계산하였다.

• Bulletin of the Korean Chemical Society
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• v.30 no.4
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• pp.849-852
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• 2009

The work describes EPR and 17O NMR measurements followed by theoretical calculation of the rotational correlation time $({\tau}_R)$, the water residence time $({\tau}_m)$, and the longitudinal electronic spin relaxation time $(T_{le})$(T_1e) for two new gadolinium complexes 1 and 2 of the type [$Gd(L)(H_2O)$] (L = tranexamic esters) in order to investigate their efficiency as a paramagnetic contrast agent (PCA). Of three correlation times, τR plays a major and predominant role to the unusually high relaxivity of 1 and 2 as compared with that of clinically approved MR CAs such as [$Gd(DTPA)(H_2O)]2‐ (Magnevist${\circledR}$), [Gd(DTPA-BMA)(H2O)] (Omniscan${\circledR}$), and $[Gd(DOTA)(H_2O)]^-$ (Dotarem${\circledR}$). The presence of bulky tranexamic ester in the ligand seems to be responsible for the conformational rigidity, which in turn causes such great an increase in ${\tau}_R$.

• Investigative Magnetic Resonance Imaging
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• v.5 no.1
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• pp.33-37
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• 2001

Purpose : The water exchange rate between bulk water and bound water is an important parameter in deciding the efficiency of paramagnetic contrast agents. In this study, we evaluated the water exchange rates of various Gd-chelates using oxygen-17 NMR technique. Material and Methods : The samples (Gd-DTPA, Gd-DTPA-BMA, Gd-DOTA, Gd-EOB-DTPA) were prepared by mixing 5% $^{17}O-enriched$ water (Isotech, USA). The pH of the samples was adjusted to physiological value [pH=7.0] by buffer solution. The variable temperature $^{17}O-NMR$ measurements were performed using Bruker-600 (14.1 T, 81.3 MHz) spectrometer. Bruker VT-1000 temperature control units were used to stabilize the temperature. The $^{17}O$ spin-spin relaxation times (T2) were measured using Carr-Purcell-Meiboom-Gill (CPMG)I pulse sequence with 24 echo trains. The variable temperature T2 relaxation data were then fitted into Solomon-Bloembergen equations using least square fit algorithm to estimate the water exchange times. Results : From the measured $^{17}O-NMR$ relaxation rates, the determined water exchange rates at 300K are $0.42{\;}{\mu}s$ for Gd-DTPA, $1.99{\;}{\mu}s$ for Gd-DTPA-BMA, $0.27{\;}{\mu}s$ for Gd-DOTA, and $0.11{\;}{\mu}s$ for Gd-EOB-DTPA. The Gd-DTPA-BMA showed slowest exchange whereas Gd-EOB-DTPA had fastest water exchange rate. In addition, it was found that the water exchange rates (${\tau}_m$) of all samples had exponential temperature dependence with different decay constant. Conclusion : $^{17}O-NMR$ relaxation rate measurements, when combined with variable temperature technique, provide a solid tool for studying water exchange rate, which is very important in investigating the detailed mechanism of relaxation enhancement effect of the paramagnetic contrast agents.

• Investigative Magnetic Resonance Imaging
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• v.2 no.1
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• pp.73-82
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• 1998

Purpose : A precise NMR technique for measuring the rate of water exchange and cell membrane permeability across the hepatocyte membrane using liver-specific MR contrast agent is described. Materials and Methods : The rat hepatocytes isolated by perfusion of the livers were used for the NMR measurements. All experiments were performed on an IBM field cycling relaxometer operating from 0.02MHz to 60 MHz proton Larmor frequency. spin-echo pulse sequence was empolyed to measure spin-lattice relaxation time, T1. The continuous distribution analysis of water proton T1 data from rat hepatocytes containing low concentrations of the liver specific contrast agent, Gd-EOB-DTPA, modeled by a general two compartment exchange model. Results : The mean residence time of water molecule inside the hepatocyte was approximately 250 msec. The lower limit for the permeability of the hepatocyte membrane was $(1.3{\pm}0.1){\;}{\times}{\;}10^{-3}cm/sec$. The CONTIN analysis, which seeks the natural distribution of relaxation times, reveals direct evidence of the effect of diffusive exchange. the diffusive water exchange is not small in the intracellular space in the case of hepatocytes. Conclusions : Gd-EOB-DTPA, when combined with continuous distribution analysis, provides a robust method to study water exchange and membrane permeability in hepatocytes. Water exchange in hepatocyte is much slower thatn that in red blood cells. Therefore, tissue-specific contrast agent may be used as a functional agent to give physiological information such as cell membrane permeability.