• Proceedings of the KSMRM Conference
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• 2001.11a
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• pp.110-110
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• 2001

목적： 최근 들어 컴퓨터 그래픽의 발전과 함께 가상 현실 등에 연구 및 응용이 급증하고 있다. 본 연구의 목적은 fMRI를 이용하여 이차원 및 삼차원 시각자극에 대한 뇌의 기능을 살펴보는 것이다. 같은 영상에 대한 2D와 3D영상을 보여 주면서, fMRI 영상 데이터를 얻었다. 사람에게 미치는 자극 중에 하나인 시각 자극에서 2D와 3D에 대해 반응하는 차이를 규명하고자 하였다. 대상 및 방법： Gradient echo를 기반으로 한 EPI 영상기법을 이용하여, 가톨릭 의대의 3.0 Tesla whole body MRI system에서 실험하였다. 해부학적 영상을 얻기 위해서는 spin echo를 이용하였다. 4명의 volunteer에 대해 같은 영상에 대한 2D와 3D영상을 보여주면서 실험을 수행하였다. 시각자극의 paradigm은 5단계 (rest, active, rest, active, rest)로 하였고, 3번의 rest와 2번의 active구간을 사이에 두었다. 각각의 구간은 10번의 iteration으로 이루어져 있고, 첫 번째 구간은 15번으로 하여 처음 5개의 결과를 버리고, 데이터를 얻었다. 결과는 spm99를 이용하여 분석하였다.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.9
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• pp.1244-1249
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• 1995

Wavelet transform technique is applied to two important electromagnetic problems:1) to analyze the frequency-domain radar echo from finite-size targets and 2) to the integral solution of two- dimensional electromagnetic scattering problems. Since the frequency- domain radar echo consists of both small-scale natural resonances and large-scale scattering center information, the multiresolution property of the wavelet transform is well suited for analyzing such ulti-scale signals. Wavelet analysis examples of backscattered data from an open- ended waveguide cavity are presented. The different scattering mechanisms are clearly resolved in the wavelet-domain representation. In the wavelet transform domain, the moment method impedance matrix becomes sparse and sparse matrix algorithms can be utilized to solve the resulting matrix equationl. Using the fast wavelet transform in conjunction with the conjugate gradient method, we present the time performance for the solution of a dihedral corner reflector. The total computational time is found to be reduced.

• Proceedings of the KSMRM Conference
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• 2003.10a
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• pp.40-40
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• 2003

The purpose of this study was to characterize focal hepatic lesions through pre and post ferucarbotran-enhanced T2 and T2＊-weighted imaging and to help differentiate benign and malignant lesions 대상 및 방법： Consecutive 34 patients with 52 hepatic lesions underwent MRI before and after intravenous bolus injection of ferucarbotran (Resovist Sobering, Berlin, Germany) for evaluation of focal hepatic lesions. Lesions included hemangiomas (n=17), metastases (n=12), cysts (n=10), hepatocellular carcinomas (n=8), dysplastic nodules (n=4), and focal fat deposit (n=1). T2-weighted fast spin echo (TR/TE： 4060/138) and gradient echo T2＊-weighted images(TR/TE： 140/5.3, FA = 90) were obtained according to the institutional routine imaging protocol. Lesional signal-intensity and lesion-to-liver contrast changes were measured by contrast-to-noise ratio (CNR) from region of interest.

• Proceedings of the KIEE Conference
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• 1999.07g
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• pp.2809-2811
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• 1999

In this paper, we develope an algorithm to calculate field inhomogeneity in MR imaging using a dual fast spin echo pulse sequence. Because phase modulation time can be easily modified with this pulse sequence, high resolution image can be obtained and acquisition time can be reduced compared to gradient echo technique. In the case of phase wrapping in field map, phase corrected using image processing technique. We assume the field pattern to be second order polynomial and apply Pseudo-Inverse equation to calculate second order polynomial coefficients. These coefficients can be used for the shimming of the magnetic field.

• Progress in Medical Physics
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• v.5 no.1
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• pp.55-66
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• 1994

After proving home-made imaging pulse sequences including tailored RF pulse by phantom, susceptibility-contrast-enhanced MR venograms of cat brain were obtained using tailored RF gradient-echo(TRGE) method. Sagittal MR imaging of the cat brain obtained by TRGE technique shows several veins, for example, dorsal sagittal sinus, straight sinus, vein of corpus callosum and internal cerebral vein, etc., compared with cats anatomical figure. Tailored RF waveform was generated by PASCAL language in ASPECT 3000 computer(Switzland, Bruker). Rectangular-shaped slice profile with bi-linear ramp function as phase distribution in the slice, at which maximum value was 2$\pi$, was fourier transformed to make tailored RF pulse. Experimental MR imaging parameters were TR/TE=205/10 msec, slice thickness TH=7mm, maxtrix size=256$\times$256, in-plane resolution=0.62$\times$0.31mm$^2$, and field of view(FOV)=8cm for both conventional gradient-echo(GE) imaging and TRGE imaging techniques.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.981-984
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• 2014

Volumetric measurement of hippocampus using IBASPM, the 20's normal adults 10 people's brain images were acquired in order to assess the changes according to the type of the Atlas. Images was obtained using MPRAGE of a 3-D gradient echo pulse sequence on Head matrix coil of 1.5T MRI system. The results of Paired t-test using obtained volume of hippocampus depending on the type of the Atlas, Atlas69-Altas84, Atlas69-Atlas116(p=0.729, 0.729) in the left hippocampus and Atlas69-Atlas84, Atlas69-Atlas116(p=0.219, 0.219) in right hippocampal formation were no significant differences but in the area except this, there was significant difference(p=0.000). The volume of the hippocampus using Atlas84 and Atlas116, represented the same value and there was no significant difference. In the image analysis using the overlay of atlas image and original image, Atlas71 could be found that the area of hippocampus did mismatch. In the case of atlas used in this study, because it has been developed by the westerners, there are differences between brain of asian. It would be needed to development of new Atlas for high accuracy measurement of the volume of hippocampus.

• Investigative Magnetic Resonance Imaging
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• v.15 no.1
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• pp.11-21
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• 2011

Purpose : Localization using MRI is difficult due to susceptibility induced artifacts caused by metal electrodes. Here we took an advantage of the B0 pattern induced by the metal electrodes by using an oblique-view imaging method. Materials and Methods : Metal electrode models with various diameters and susceptibilities were simulated to understand the aspect of field distortion. We set localization criteria for a turbo spin-echo (TSE) sequence usingconventional ($90^{\circ}$ view) and $45^{\circ}$ oblique-view imaging method through simulation of images with various resolutions and validated the criteria usingphantom images acquired by a 3.0T clinical MRI system. For a gradient-refocused echo (GRE) sequence, which is relatively more sensitive to field inhomogeneity, we used phase images to find the center of electrode. Results : There was least field inhomogeneity along the $45^{\circ}$ line that penetrated the center of the electrode. Therefore, our criteria for the TSE sequence with $45^{\circ}$ oblique-view was coincided regardless of susceptibility. And with $45^{\circ}$ oblique-view angle images, pixel shifts were bidirectional so we can detect the location of electrodes even in low resolution. For the GRE sequence, the $45^{\circ}$ oblique-view anglemethod madethe lines where field polarity changes become coincident to the Cartesian grid so the localization of the center coordinates was more facilitated. Conclusion : We suggested the method for accurate localization of electrode using $45^{\circ}$ oblique-view angle imaging. It is expected to be a novelmethodto monitoring an electrophysiological brain study and brain neurosurgery.

• Investigative Magnetic Resonance Imaging
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• v.12 no.2
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• pp.142-147
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• 2008

Purpose : By using the micro-imaging unit modified from NMR spectrometer, the high resolution MRI protocols of finer than 100 micron in 5 minutes, is sought for mouse, which plays a central role in animal studies Materials and Methods : C57BL/6 mouse, lighter than 50 gram, is used for the experiments. The superconducting magnet is vertical type with 89 mm inner diameter at 4.9 Tesla. The diameter of rf-coil is 30 mm. Mostly used techniques are the fast spin echo and the gradient echo pulse sequence. Results : For 2D images, proton density and T2 weighted images are obtained and their optimum experimental variables were sought. Minute structure of mouse brain can be recognized and 3D brain image is also obtained additionally. 3D image will be useful particularly for the dynamic contrast study using various contrast agents. Conclusion : Like the case of human and other small animals, the high resolution of mouse brain is enough to recognize the minute structure of it. Recently, similar studies are reported domestically, but it seems only a beginning stage. Due to easiness of breeding/control, mouse MRI study will soon play a vital part in brain study.

• Investigative Magnetic Resonance Imaging
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• v.19 no.2
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• pp.76-87
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• 2015

Purpose: There is an ongoing search for a stent material that produces a reduced susceptibility artifact. This study evaluated the effect of manganese (Mn) content on the MRI susceptibility artifact of ferrous-manganese (Fe-Mn) alloys, and investigated the correlation between MRI findings and measurements of Fe-Mn microstructure on X-ray diffraction (XRD). Materials and Methods: Fe-Mn binary alloys were prepared with Mn contents varying from 10% to 35% by weight (i.e., 10%, 15%, 20%, 25%, 30%, and 35%; designated as Fe-10Mn, Fe-15Mn, Fe-20Mn, Fe-25Mn, Fe-30Mn, and Fe-35Mn, respectively), and their microstructure was evaluated using XRD. Three-dimensional spoiled gradient echo sequences of cylindrical specimens were obtained in parallel and perpendicular to the static magnetic field (B0). In addition, T1-weighted spin echo, T2-weighted fast spin echo, and $T2^*$weighted gradient echo images were obtained. The size of the low-intensity area on MRI was measured for each of the Fe-Mn binary alloys prepared. Results: Three phases of ${\alpha}^{\prime}$-martensite, ${\gamma}$-austenite, and ${\varepsilon}$-martensite were seen on XRD, and their composition changed from ${\alpha}^{\prime}$-martensite to ${\gamma}$-austenite and/or ${\varepsilon}$-martensite, with increasing Mn content. The Fe-10Mn and Fe-15Mn specimens comprised ${\alpha}^{\prime}$-martensite, the Fe-20Mn and Fe-25Mn specimens comprised ${\gamma}+{\varepsilon}$ phases, and the Fe-30Mn and Fe-35Mn specimens exhibited a single ${\gamma}$ phase. The size of the low-intensity areas of Fe-Mn on MRI decreased relative to its microstructure on XRD with increasing Mn content. Conclusion: Based on these findings, proper conditioning of the Mn content in Fe-Mn alloys will improve its visibility on MR angiography, and a Mn content of more than 25% is recommended to reduce the magnetic susceptibility artifacts on MRI. A reduced artifact of Fe-Mn alloys on MRI is closely related to the paramagnetic constitution of ${\gamma}$-austenite and/or ${\varepsilon}$-martensite.

• Investigative Magnetic Resonance Imaging
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• v.25 no.3
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• pp.141-155
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• 2021

Purpose: To develop a 3D magnetic resonance fingerprinting (MRF) method for application in high resolution knee cartilage PD, T₁, T₂ mapping. Materials and Methods: A novel 3D acquisition trajectory with golden-angle rotating radial in k_xy direction and interleaved echo planar imaging (EPI) acquisition in the k_z direction was implemented in the MRF framework. A centric order was applied to the interleaved EPI acquisition to reduce Nyquist ghosting artifact due to field inhomogeneity. For the reconstruction, singular value decomposition (SVD) compression method was used to accelerate reconstruction time and conjugate gradient sensitivity-encoding (CG-SENSE) was performed to overcome low SNR of the high resolution data. Phantom experiments were performed to verify the proposed method. In vivo experiments were performed on 6 healthy volunteers and 2 early osteoarthritis (OA) patients. Results: In the phantom experiments, the T₁ and T₂ values of the proposed method were in good agreement with the spin-echo references. The results from the in vivo scans showed high quality proton density (PD), T₁, T₂ map with EPI echo train length (N_ETL = 4), acceleration factor in through plane (R_z = 5), and number of radial spokes (N_spk = 4). In patients, high T₂ values (50-60 ms) were seen in all transverse, sagittal, and coronal views and the damaged cartilage regions were in agreement with the hyper-intensity regions shown on conventional turbo spin-echo (TSE) images. Conclusion: The proposed 3D MRF method can acquire high resolution (0.5 mm³) quantitative maps in practical scan time (~ 7 min and 10 sec) with full coverage of the knee (FOV: 160 × 160 × 120 mm³).