• Korean Journal of Digital Imaging in Medicine
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• v.15 no.2
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• pp.63-68
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• 2013

Purpose : The relaxation times of tissue in MRI depend on strength of magnetic field, morphology of nuclear, viscosity, size of molecules and temperature. This study intended to analyze quantitatively that materials' temperatures have effects on T1 and T2 relaxation times without changing of other conditions. Materials and Methods : The equipment was used MAGNETOM SKYRA of 3.0T(SIEMENS, Erlagen, Germany), 32 channel spine coil and Gd-DTPA water concentration phantom. To find out T1 relaxation time, Inversion Recovery Spin Echo sequences were used at 50, 400, 1100, 2500 ms of TI. To find out T2 relaxation time, Multi Echo Spin Echo sequences were used at 30, 60, 90, 120, 150, 180, 210, 240, 270 ms of TE. This experiment was scanned with 5 steps from 25 to $45^{\circ}C$. next, using MRmap(Messroghli, BMC Medical Imaging, 2012) T1 and T2 relaxation times were mapped. on the Piview STAR v5.0(Infinitt, Seoul, Korea) 5 steps were measured as the same ROI, and then mean values were calculated. Correlation between the temperatures and relaxation times were analyzed by SPSS(version 17.0, Chicago, IL, USA). Results : According to increase of temperatures, T1 relaxation times were $214.39{\pm}0.25$, $236.02{\pm}0.87$, $267.47{\pm}0.48$, $299.44{\pm}0.64$, $330.19{\pm}1.72$ ms. T2 relaxation times were $180.17{\pm}0.27$, $197.17{\pm}0.44$, $217.92{\pm}0.39$, $239.89{\pm}0.53$, $257.40{\pm}1.77$ ms. With the correlation analysis, the correlation coefficients of T1 and T2 relaxation times were statistically significant at 0.998 and 0.999 (p< 0.05). Conclusion : T1 and T2 relaxation times are increased as temperature of tissue goes up. In conclusion, we suggest to recognize errors of relaxation time caused local temperature's differences, and consider external factors as well in the quantitative analysis of relaxation time or clinical tests.

• Korean Journal of Radiology
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• v.2 no.2
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• pp.63-67
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• 2001

Objective: Atrophy and a high T2 signal of the hippocampus are known to be the principal MR imaging findings of hippocampal sclerosis. The purpose of this study was to determine whether or not individual MRI findings correlate with surgical outcome in patients with this condition. Materials and Methods: Preoperative MR imaging findings in 57 consecutive patients with pathologically-proven hippocampal sclerosis who underwent anterior temporal lobectomy and were followed-up for 24 months or more were retrospectively reviewed, and the results were compared with the postsurgical outcome (Engel classification). The MR images included routine sagittal T1-weighted and axial T2-weighted spin-echo images, and oblique coronal T1-weighted 3D gradient-echo and T2-weighted 2D fast spin-echo images obtained on either a 1.5 T or 1.0 T unit. The images were visually evaluated by two neuroradiologists blinded to the outcome; their focus was the presence or absence of atrophy and a high T2 hippocampal signal. Results: Hippocampal atrophy was seen in 96% of cases (55/57) [100% (53/53) of the good outcome group (Engel class I and II), and 50% (2/4) of the poor outcome group (class III and IV)]. A high T2 hippocampal signal was seen in 61% of cases (35/57) [62% (33/53) of the good outcome group and 50% (2/4) of the poor outcome group]. All 35 patients with a high T2 signal had hippocampal atrophy. 'Normal' hippocampus, as revealed by MR imaging, occurred in 4% of patients (2/57), both of whom showed a poor outcome (Engel class III). The presence or absence of hippocampal atrophy correlated well with surgical outcome (p<0.01). High T2 signal intensity did not, however, significantly correlate with surgical outcome (p>0.05). Conclusion: Compared with a high T2 hippocampal signal, hippocampal atrophy is more common and correlates better with surgical outcome. For the prediction of this, it thus appears to be the more useful indicator.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.40 no.5
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• pp.341-349
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• 2003

A real time interactive controller (spectrometer) for magnetic resonance imaging (MRI) system has been developed using high speed digital signal processors (DSP). The controller generates radio frequency (rf) waveforms and audio frequency gradient waveforms and controls multiple receivers for data acquisition. By employing DSPs having high computational power (e.g., TMS320C670l) real time generation of complicated gradient waveforms and interactive control of selection planes are possible, which are important features in real-time imaging of moving organs, e.g., cardiac imaging. The spectrometer was successfully implemented at a 1.5 Tesla whole body MRI system for clinical application. Performance of the spectrometer is verified by various experiments including high- speed imaging such as fast spin echo (FSE) and echo planar imaging (EPI). These high-speed imaging techniques reduce measurement time, however, usually intensify artifact if there is any systematic phase error or jitter in the synchronization between the transmitter, receiver, and gradients.

• Imaging Science in Dentistry
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• v.51 no.4
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• pp.413-419
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• 2021

Purpose: The aim of this in vitro study was to assess the role of bandwidth on the area of magnetic resonance imaging (MRI) artifacts caused by orthodontic appliances composed of different alloys, using different pulse sequences in 1.5 T and 3.0 T magnetic fields. Materials and Methods: Different phantoms containing orthodontic brackets (ceramic, ceramic bracket with a stainless-steel slot, and stainless steel) were immersed in agar gel and imaged in 1.5 T and 3.0 T MRI scanners. Pairs of gradient-echo (GE), spin-echo (SE), and ultrashort echo time (UTE) pulse sequences were used differing in bandwidth only. The area of artifacts from orthodontic devices was automatically estimated from pixel value thresholds within a region of interest (ROI). Mean values for similar pulse sequences differing in bandwidth were compared at 1.5 T and 3.0 T using analysis of variance. Results: The comparison of groups revealed a significant inverse association between bandwidth values and artifact areas of the stainless-steel bracket and the self-ligating ceramic bracket with a stainless-steel slot(P<0.05). The areas of artifacts from the ceramic bracket were the smallest, but were not reduced significantly in pulse sequences with higher bandwidth values(P<0.05). Significant differences were also observed between 1.5 T and 3.0 T MRI using SE and UTE, but not using GE 2-dimensional or 3-dimensional pulse sequences. Conclusion: Higher receiver bandwidth might be indicated to prevent artifacts from orthodontic appliances in 1.5 T and 3.0 T MRI using SE and UTE pulse sequences.

• 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.

• Journal of the Korean Magnetic Resonance Society
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• v.5 no.1
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• pp.1-12
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• 2001

ZSM-5 gallosilicate molecular sieves was synthesized and cupric ion was ion-exchanged into the gallosilicate. The locations of Cu(ll) species in the framework and their interactions with various adsorbates were characterized by combined electron spin resonance(ESR) and electron spin echo modulation(ESEM) methods. It was found that in a fresh hydrated material, Cu(II) is octahedrally coordinated to six water molecules. This species is located in the channel intersections of two sinusoidal channels and rotates rapidly at room temperature. Evacuation removes some of these water molecules, leaving the Cu(II) coordinated to less water molecules and anchored to of oxygens in the channel wall. Dehydration produces two Cu(II) species, both of which are located in sites inaccessible to oxygen as evidenced by non-broadening of its ESR lines by oxygen. Adsorption of adsorbate molecules such as water, alcohols, ammonia, acetonitrile and ethylene on dehydrated CuNaH-ZSM-5 gallosilicate materials causes changes in the ESR spectrum of Cu(II), indicating the migration of Cu(II) into main channels to form complexes with these adsorbates there. Cu(II) forms a complex with two molecules of methanol, ethanol and propanol, respectively as evidenced by ESR parameters and ESEM data. Cu(II) also forms a square planar complex with four molecules of ammonia, based on the resolved nitrogen superhyperfine interactions and their ESEM parameters. Cu(II) forms a complex with two molecules of acetonitrile based on the ESR parameters and ESEM data. Interestingly, however, only part of Cu(II) interacts indirectly with one molecule of nonpolar ethylene based on ESR and ESEM analyses.

• Investigative Magnetic Resonance Imaging
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• v.17 no.2
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• pp.133-143
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• 2013

Purpose : To evaluate and compare the accuracy of magnetic resonance imaging (MRI) and ultrasound (US) for detection and estimation of invasion depth of colorectal carcinoma (CRC) by correlation with histopathologic findings in vitro, and to find out the best MR pulse sequence for accurate delineation of tumor from surrounding normal tissue. Materials and Methods: Resected specimens of CRC from 45 patients were examined about tumor detectability and invasion depth of US using high frequency (5-17 MHz) linear transducer in a tube filled with normal saline and MRI in a 8-channel quadrate head coil. The institutional review board approved this study and informed consent was waived. MRI with seven pulse sequences of in- and out-of-phases gradient echo T1 weighted images, fast spin echo T2 weighted image and its fat suppression image, fast imaging employing steady-state acquisition (FIESTA) and its fat suppression image, and diffusion weighted image (DWI) were performed. In each case, both imaging findings of MRI and US were evaluated independently for detection and estimation of invasion depth of tumor by consensus of two radiologists and were compared about diagnostic accuracy according to the histopathologic findings as reference standard. Seven MR pulse sequences were evaluated on the point of accurate delineation of tumor from surrounding normal tissue in each specimen. Results: In specimens of CRC, both imaging modalities of MRI (91.1%) and US (86.7%) showed relatively high diagnostic accuracy to detect tumor and evaluate invasion depth of tumor. In early CRC, diagnostic accuracy of US was 87.5% and that of MRI was 75.0%. There was no statistically significant difference between two imaging modalities (p > 0.05). The best pulse sequence among seven MR sequences for accurate delineation of tumor from surrounding normal tissue in each specimen of CRC was fast spin echo T2 weighted image. Conclusion: MRI and US show relatively high diagnostic accuracy to detect tumor and evaluate invasion depth of resected specimen of CRC. The most excellent pulse sequence of MRI for accurate delineation of tumor from surrounding normal tissue in CRC is fast spin echo T2 weighted image.

• Bulletin of the Korean Chemical Society
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• v.32 no.6
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• pp.1970-1974
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• 2011

The effects of convection on the measurement of the diffusion coefficients of liquids by the pulsed gradient spin echo (PGSE) NMR method at low temperature are discussed. To examine the generation of convective flows, we used four different types of sample tubes in the diffusion measurements with temperature variation; a normal 5 mm NMR tube, a Shigemi tube, an ELISE type tube, and a capillary tube. Below room temperature, the calculated diffusion coefficients of chloroform in 5 mm o.d. type tubes increased with decreasing temperature, while those in the capillary tube decreased linearly. The convective flow was found to be significant even at low temperature and it seemed to be mainly induced by the transverse temperature gradient. It was also found that the capillary tube was most appropriate to measure the diffusion coefficients, since its small diameter is effective in suppressing the convective flows at both high and low temperatures.

• Proceedings of the KSMRM Conference
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• 2001.11a
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• pp.166-166
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• 2001

목적： 척수의 질환에 대한 확산강조영상 소견에 대하여 알아본다. 대상 및 방법： 임상적으로 진단된 척수질환 환자 8명을 (acute transverse myelitis (n=3), spinal dural AV fistula (n=2), multiple sclerosis (n=1), spinal cord tumor (n=2)) 대상으로 하였다. 영상은 Philips Intera 1.5 T system을 이용하였고, multishot spin echo EPI 펄스열 및 EKG gating을 이용하여 영상을 얻었다. 3R-R 간격으로 영상을 얻었으며 TE=72msec, FOV=25cm, 256 matrix, 5mm thickness, b value=400으로 영상매개변수를 정하였다. 척수 중심으로 3개의 절편을 얻었으며 T2 강조 영상과 겉보기확산계수 영상을 같이 구하였다.

• Proceedings of the KSMRM Conference
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• 2001.11a
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• pp.146-146
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• 2001

목적： 해상도가 우수한 경직장 영상을 위한 소아용 two-turn 표면형 수신 코일, 안장 수신 코일을 제작하여 이를 이용하여 얻은 고양이의 경직장 영상을 비교한다. 대상 및 방법： 지금까지 소아의 경직장 영상은 주로 초음파를 이용하여 얻었으나 해상도가 떨어지며 아직까지 소아용 탐촉자는 개발되지 않았다. 소아의 항문직장 기형의 진단을 위해서는 해상도가 우수한 영상이 필요하고, 이를 위해 소아용 직장 RF 코일로 원주형 two-turn 표면형 코일, 안장 코일을 제작하였다. 크기는 직경 7mm, 길이 6cm와, 직경 10mm, 길이 l0cm 하였고, 코일의 구리선 바깥으로는 두께 1mm의 테프론 tube로 감쌌다. 균일한 시험 시료(phantom)로 마요네즈를 이용하여 T1 강조 영상(Spin echo TR/TE= 500/11 msec, FOV=12cm, 영상행렬 256$\times$256)을 얻어서 신호 강도의 profile을 얻는다. 이를 Mathematica를 이용하여 구한 RF 자기장 세기의 분포와 비교했다. 두 종류의 코일을 각각 사용하여 얻은 고양이 항문 괄약근 영상에서 외부 괄약근, 내부 괄약근 등을 구분, 비교하였다.