• Investigative Magnetic Resonance Imaging
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• v.12 no.1
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• pp.20-26
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• 2008

Purpose : To present the T1 and T2 relaxation times of the major cerebral metabolites at 1.5T and 3.0T and compare those between 1.5T and 3.0T. Materials and Methods : Using the phantom containing N-acetyl aspartate (NAA), Choline (Cho), and Creatine (Cr) at both 1.5T and 3.0T MRI, the T1 relaxation times were calculated from the spectral data obtained with 5000 ms repetition time (TR), 20 ms echo time (TE), and 11 different mixing time (TM)s using STEAM (STimulated Echo-Acquisition Mode) method. The T2 relaxation times were obtained from the spectral data obtained with 3000 ms TR and 5 different TEs using PRESS (Point-RESolved Spectroscopy) method. The T1 and T2 relaxation times obtained at 1.5T were compared with those of 3.0T. Results : The T1 relaxation times of NAA were $2293\;{\pm}\;48\;ms$ at 1.5T and $2559\;{\pm}\;124\;ms$ at 3.0T (11.6% increase at 3.0T). The T1 relaxation times of Cho were $2540\;{\pm}\;57\;ms$ at 1.5T and $2644\;{\pm}\;76\;ms$ at 3.0T (4.1% increase at 3.0T). The T1 relaxation times of Cr were $2543\;{\pm}\;75\;ms$ at 1.5T and $2665\;{\pm}\;94\;ms$ at 3.0T (4.8% increase). The T2 relaxation times of NAA were $526\;{\pm}\;81\;ms$ at 1.5T and $468\;{\pm}\;74\;ms$ at 3.0T (11.0% decrease at 3.0T). The T2 relaxation times of Cho were $220\;{\pm}\;44ms$ at 1.5T and $182\;{\pm}\;35\;ms$ at 3.0T (17.3% decrease at 3.0T). The T2 relaxation times of Cr were $289\;{\pm}\;47\;ms$ at 1.5T and $275\;{\pm}\;57\;ms$ at 3.0T (4.8% decrease at 3.0T). Conclusion : The T1 relaxation times of the major cerebral metabolites (NAA, Cr, Cho), which were measured at the phantom, were 4.1%-11.6% longer at 3.0T than at 1.5T. The T2 relaxation times of them were 4.8%-17.3% shorter at 3.0T than at 1.5T. To optimize MR spectroscopy at 3.0T, TR should be lengthened and TE should be shortened.

• Investigative Magnetic Resonance Imaging
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• v.6 no.2
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• pp.120-128
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• 2002

Purpose : To demonstrate that the relaxographic method provides additional information such as the distribution of relaxation times and water content which are poentially applicable to clinical medicine. Materials and Methods : First, the computer simulation was performed with the generated relaxation data to verify the accuracy and reliabilility of the relaxographic method (CONTINI). Secondly, in or der to see how well the CONTIN quantifies and resolves the two different ${T_1}$ environments, we calculated the oil to water peak area ratios and identified peak positions of ${T_1}-distribution$ curve of the phantom solutions, which consist of four centrifugal tubes (10 ml) filled with the compounds of 0, 10, 20, 30% of corn oil and distilled water, using CONTIN. Finally, inversion recovery MR images for a volunteer are acquired for each TI ranged from 40 to 1160 msec with TR/TE=2200/20 msec. From the 3 different ROIs (GM, WM, CSF), CONTIN analysis was performed to obtain the ${T_1}$-distribution curves, which gave peak positions and peak area of each ROI location. Results : The simulation result shows that the errors of peak positions were less in the higher peak (centered ${T_1}=600$ msec) than in the lower peak (centered ${T_1}=150$ msec) for all SNR but the errors of peak areas were larger in the higher peak than in the lower peak. The CONTIN analysis of the measured relaxation data of phantoms revealed two peaks between 20 and 60 msec and between 500 and 700 msec. The analysis gives the peak area ratio as oil 10%: oil 20%: oil 30% = 1:1.3:1.9, which is different from the exact ratio, 1:2:3. For human brain, in ROI 3 (CSF), only one component of -distributions was observed whereas in ROI 1(GM) and in ROI 2 (WM) we observed two components of ${T_1}-distribution$. For the WM and CSF there was great agreement between the observed ${T_1}-relaxation$ times and the reported values. Conclusion : we demonstrated that the relaxographic method provided additional information such as the distribution of relaxation times and water content, which were not available in the routine relaxometry and ${T_1}/{T_2}$ mapping techniques. In addition, these additional information provided by relaxographic analysis may have clinical importance.

• Investigative Magnetic Resonance Imaging
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• v.2 no.1
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• pp.67-72
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• 1998

The mapping of the spin-spin relaxation time T2 in pixel-by-pixel was suggested as a quantitative diagnostic tool in medicine. although the CPMG pulse sequence has been known to be the best pulse sequence for T2 measurement in physics NMR, the supplied pulse sequence by the manufacture of MRI system was able to obtain the maximum of 4 CPMG images. Eight or more images with different echo time TEs are required to construct a reliable T2 map, so that two or more acquisitions were required, which easily took more than 10 minutes. 4-echo CPMG imaging pulse sequence was modified to generate the maximum of 8 MR images with evenly spaced echo time TEs. In human MR imaging, since patients tend to move at least several pixels between the different acquisitions, 8-echo CPMG imaging sequence reduces the acquisition time and may remove any mis-regitration of each pixels signal for the fitting of T2. The resultant T2 maps using the theoretically simulated images and using the MR images of the human brain suggested that 8 echo CPMG sequence with short echo spacing such as 17-20 msec can give the reliable T2 map.

• Investigative Magnetic Resonance Imaging
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• v.13 no.1
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• pp.9-14
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• 2009

T1-, and T2-weighted imagings and FLAIR (fluid attenuated inversion recovery) imaging are fundamental imaging methods in the brain. T1-weighted imaging is a spin-echo sequence with short TR and short TE and produces the tissue contrast by different T1 relaxation times. In other words, short TR maximizes the difference of the longituidinal magnetization recovery between the tissues. T2-weighted imaging is a spin-echo sequence with long TR and long TE and produces the tissue contrast by different T2 relaxation times. Long TE maximizes the difference of the transverse magnetization decay between the tissues. FLAIR is an inversion recovery sequence using 180 degree inversion pulse. 2500 msec of inversion time is applied to suppress the CSF signal.

• Progress in Medical Physics
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• v.17 no.2
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• pp.61-66
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• 2006

To evaluate the T1, T2 magnetic relaxation properties of water molecule according to molecular weight of paramagnetic complex. 4-aminomethyicyclohexane carboxylic acid (0.63 g, 4 mmol) was mixed with the suspension solution of DMF (15 ml) and DTPA-bis-anhydride (0.71 g, 2 mmol) to synthesize the ligand. The ligand was then mixed with $Gd_2O_3$ (0.18 g, 0.5 mmol) to synthesize Gd-chelate. For the measurement of magnetic relaxivity of paramagnetic compounds, the compounds were diluted to 1 mM and then the relaxation times were measured at 1.57 (64 MHz). Inversion-recovery pulse sequence was employed for T1 relaxation measurement and CPMG (Carr-Purcell-Meiboon-Gill) pulse sequence was employed for T2 relaxation measurement. In case of inversion recovery sequence, total 35 images with different inversion time(T1)s ranging from 50 msec to 1,750 msec. To estimate the relaxation times, the signal intensity of each sample was measured using region of Interest (ROI) and then fitted by non-linear least square method to yield T1, T2 relaxation times and also R1 and R2. Compared to T1=($205.1{\pm}2.57$) msec and T2=($209.4{\pm}4.28$) msec of Omniscan (Gadodiamide), which is commercially available paramagnetic MR agent, T1 and T2 values of new paramagnetic complexes were reduced along with their molecular weight. That is, T1 value was ranged from $(96.35{\pm}2.04)\;to\;(79.38{\pm}1.55)$ msec and T2 value was ranged from $(91.02{\pm}2.08)\;to\;(76.66{\pm}1.84)$ msec. Among new paramagnetic complexes, there is a tendency that the R1 and R2 increase as the molecular weight is increases. As molecular weight of paramagnetic complex increases, T1 and T2 relaxation times reduce and thus the increase of relaxivity (R1 and R2) Is proportional to molecular weight.

• Journal of radiological science and technology
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• v.41 no.1
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• pp.25-31
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• 2018

This study aimed to evaluate the range of maximum TE that could measure T2 relaxation time accurately by setting diverse maximum TE with using contrast medium phantoms. Contrast medium phantoms ranging from low to high concentrations were made by using Gadoteridol. The relaxation time and relaxation rate were compared and evaluated by conducting T2 mapping by using reference data based on various TEs and data obtained from different maximum TEs. It was found that accurate T2 relaxation time could be expressed only when the maximum TE over a certain range was used in the section with long T2 relaxation time, such as the low concentration section of saline or gadolinium contrast medium. Therefore, the maximum TE shall be longer than the T2 relation time for accurately maturing the T2 relaxation of a certain tissue or a substance.

• Investigative Magnetic Resonance Imaging
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• v.7 no.1
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• pp.39-46
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• 2003

Purpose : To develop a theoretical model for magnetic relaxation behavior of the superparamagnetic nano-particle agent, which demonstrates multi-functionality such as liver- and lymp node-specificity. Based on the developed model, the computer simulation was performed to clarify the relationship between relaxation time and the applied magnetic field strength. Materials and Methods : The ultrasmall superparamagnetic iron oxide (USPIO) was encapsulated with biocompatiable polymer, to develop a relaxation model based on outsphere mechanism, which was resulting from diffusion and/or electron spin fluctuation. In addition, Brillouin function was introduced to describe the full magnetization by considering the fact that the low-field approximation, which was adapted in paramagnetic case, is no longer valid. The developed model describes therefore the T1 and T2 relaxation behavior of superparamagnetic iron oxide both in low-field and in high-field. Based on our model, the computer simulation was performed to test the relaxation behavior of superparamagnetic contrast agent over various magnetic fields using MathCad (MathCad, U.S.A.), a symbolic computation software. Results : For T1 and T2 magnetic relaxation characteristics of ultrasmall superparamagnetic iron oxide, the theoretical model showed that at low field (<1.0 Mhz), $\tau_{S1}(\tau_{S2}$, in case of T2), which is a correlation time in spectral density function, plays a major role. This suggests that realignment of nano-magnetic particles is most important at low magnetic field. On the other hand, at high field, $\tau$, which is another correlation time in spectral density function, plays a major role. Since $\tau$ is closely related to particle size, this suggests that the difference in R1 and R2 over particle sizes, at high field, is resulting not from the realignment of particles but from the particle size itself. Within normal body temperature region, the temperature dependence of T1 and T2 relaxation time showed that there is no change in T1 and T2 relaxation times at high field. Especially, T1 showed less temperature dependence compared to T2. Conclusion : We developed a theoretical model of r magnetic relaxation behavior of ultrasmall superparamagnetic iron oxide (USPIO), which was reported to show clinical multi-functionality by utilizing physical properties of nano-magnetic particle. In addition, based on the developed model, the computer simulation was performed to investigate the relationship between relaxation time of USPIO and the applied magnetic field strength.

• Investigative Magnetic Resonance Imaging
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• v.18 no.1
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• pp.1-6
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• 2014

Purpose : $T_2{^*}$ relaxation time which includes susceptibility information represents unique feature of tissue. The objective of this study was to investigate $T_2{^*}$ relaxation times of the normal glandular tissue and fat of breast using a 3T MRI system. Materials and Methods: Seven-echo MR Images were acquired from 52 female subjects (age $49{\pm}12 $years; range, 25 to 75) using a three-dimensional (3D) gradient-echo sequence. Echo times were between 2.28 ms to 25.72 ms in 3.91 ms steps. Voxel-based $T_2{^*}$ relaxation times and $R_2{^*}$ relaxation rate maps were calculated by using the linear curve fitting for each subject. The 3D regions-of-interest (ROI) of the normal glandular tissue and fat were drawn on the longest echo-time image to obtain $T_2{^*}$ and $R_2{^*}$ values. Mean values of those parameters were calculated over all subjects. Results: The 3D ROI sizes were $4818{\pm}4679$ voxels and $1455{\pm}785$ voxels for the normal glandular tissue and fat, respectively. The mean $T_2{^*}$ values were $22.40{\pm}5.61ms$ and $36.36{\pm}8.77ms$ for normal glandular tissue and fat, respectively. The mean $R_2{^*}$ values were $0.0524{\pm}0.0134/ms$ and $0.0297{\pm}0.0069/ms$ for the normal glandular tissue and fat, respectively. Conclusion: $T_2{^*}$ and $R_2{^*}$ values were measured from human breast tissues. $T_2{^*}$ of the normal glandular tissue was shorter than that of fat. Measurement of $T_2{^*}$ relaxation time could be important to understand susceptibility effects in the breast cancer and the normal tissue.

• Investigative Magnetic Resonance Imaging
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• v.8 no.2
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• pp.100-108
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• 2004

Purpose : Early degeneration of articular cartilage is accompanied by a loss of glycosaminoglycan (GAG) and the consequent change of the integrity. The purpose of this study was to biochemically quantify the loss of GAG, and to evaluate the $Gd(DTPA)^{2-}$-enhanced, and T1, T2, rho relaxation map for detection of the early degeneration of cartilage. Materials and Methods : A cartilage-bone block in size of $8mm\;\times\;10mm$ was acquired from the patella in each of three pigs. Quantitative analysis of GAG of cartilage was performed at spectrophotometry by use of dimethylmethylene blue. Each of cartilage blocks was cultured in one of three different media: two different culture media (0.2 mg/ml trypsin solution, 1mM Gd $(DTPA)^{2-}$ mixed trypsin solution) and the control media (phosphate buffered saline (PBS)). The cartilage blocks were cultured for 5 hrs, during which MR images of the blocks were obtained at one hour interval (0 hr, 1 hr, 2 hr, 3 hr, 4 hr, 5 hr). And then, additional culture was done for 24 hrs and 48 hrs. Both T1-weighted image (TR/TE, 450/22 ms), and mixed-echo sequence (TR/TE, 760/21-168ms; 8 echoes) were obtained at all times using field of view 50 mm, slice thickness 2 mm, and matrix $256\times512$. The MRI data were analyzed with pixel-by-pixel comparisons. The cultured cartilage-bone blocks were microscopically observed using hematoxylin & eosin, toluidine blue, alcian blue, and trichrome stains. Results : At quantitation analysis, GAG concentration in the culture solutions was proportional to the culture durations. The T1-signal of the cartilage-bone block cultured in the $Gd(DTPA)^{2-}$ mixed solution was significantly higher ($42\%$ in average, p<0.05) than that of the cartilage-bone block cultured in the trypsin solution alone. The T1, T2, rho relaxation times of cultured tissue were not significantly correlated with culture duration (p>0.05). However the focal increase in T1 relaxation time at superficial and transitional layers of cartilage was seen in $Gd(DTPA)^{2-}$ mixed culture. Toluidine blue and alcian blue stains revealed multiple defects in whole thickness of the cartilage cultured in trypsin media. Conclusion : The quantitative analysis showed gradual loss of GAG proportional to the culture duration. Microimagings of cartilage with $Gd(DTPA)^{2-}$-enhancement, relaxation maps were available by pixel size of $97.9\times195\;{\mu}m$. Loss of GAG over time better demonstrated with $Gd(DTPA)^{2-}$-enhanced images than with T1, T2, rho relaxation maps. Therefore $Gd(DTPA)^{2-}$-enhanced T1-weighted image is superior for detection of early degeneration of cartilage.

• 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.