• Investigative Magnetic Resonance Imaging
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• 제23권1호
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• pp.38-45
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• 2019

Purpose: To demonstrate the high-resolution numerical simulation of the respiration-induced dynamic $B_0$ shift in the head using generalized susceptibility voxel convolution (gSVC). Materials and Methods: Previous dynamic $B_0$ simulation research has been limited to low-resolution numerical models due to the large computational demands of conventional Fourier-based $B_0$ calculation methods. Here, we show that a recently-proposed gSVC method can simulate dynamic $B_0$ maps from a realistic breathing human body model with high spatiotemporal resolution in a time-efficient manner. For a human body model, we used the Extended Cardiac And Torso (XCAT) phantom originally developed for computed tomography. The spatial resolution (voxel size) was kept isotropic and varied from 1 to 10 mm. We calculated $B_0$ maps in the brain of the model at 10 equally spaced points in a respiration cycle and analyzed the spatial gradients of each of them. The results were compared with experimental measurements in the literature. Results: The simulation predicted a maximum temporal variation of the $B_0$ shift in the brain of about 7 Hz at 7T. The magnitudes of the respiration-induced $B_0$ gradient in the x (right/left), y (anterior/posterior), and z (head/feet) directions determined by volumetric linear fitting, were < 0.01 Hz/cm, 0.18 Hz/cm, and 0.26 Hz/cm, respectively. These compared favorably with previous reports. We found that simulation voxel sizes greater than 5 mm can produce unreliable results. Conclusion: We have presented an efficient simulation framework for respiration-induced $B_0$ variation in the head. The method can be used to predict $B_0$ shifts with high spatiotemporal resolution under different breathing conditions and aid in the design of dynamic $B_0$ compensation strategies.

• Annals of Clinical Neurophysiology
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• 제4권1호
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• pp.21-27
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• 2002

Background : Spatial analysis of EEG is a phenomenal assessment and not so informative for phase space and dynamic aspect of EEG data. In contrast, nonlinear EEG analysis attempts to characterize the dynamics of neural networks in the brain. We have analyzed the features of EEG nonlinearly in subjects with white matter change on brain MRI and compared the results with cognitive function in each. Methods : Digital EEG data were taken for 30 seconds in 9 subjects with white matter degeneration and in 5 healthy normal controls without white matter change on MRI. Then we analyzed them nonlinearly to calculate the correlation dimension(D2) using the MATLAB software. The cognitive function was assessed by 3MS(modified mini-mental state examination). The severity of white matter change was assessed by Scheltens scale. Results : The mean D2 value of normal control was greater than that of white matter degeneration group. The D2s of some channels were correlative with 3MS and degree of white matter degeneration significantly. Conclusions : nonlinear analysis of EEG can be used as one of adjuvant functional studies for prediction of cognitive impairment in subjects with white matter degeneration and subcortical white matter change can be influential on cognitive function and correlation dimension of EEG.

• Nuclear Engineering and Technology
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• 제38권4호
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• pp.327-342
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• 2006

Radiation therapy is an important part of cancer treatment in which cancer patients are treated using high-energy radiation such as x-rays, gamma rays, electrons, protons, and neutrons. Currently, about half of all cancer patients receive radiation treatment during their whole cancer care process. The goal of radiation therapy is to deliver the necessary radiation dose to cancer cells while minimizing dose to surrounding normal tissues. Success of radiation therapy highly relies on how accurately 1) identifies the target and 2) aim radiation beam to the target. Both tasks are strongly dependent of imaging technology and many imaging modalities have been applied for radiation therapy such as CT (Computed Tomography), MRI (Magnetic Resonant Image), and PET (Positron Emission Tomogaphy). Recently, many researchers have given significant amount of effort to develop and improve imaging techniques for radiation therapy to enhance the overall quality of patient care. For example, advances in medical imaging technology have initiated the development of the state of the art radiation therapy techniques such as intensity modulated radiation therapy (IMRT), gated radiation therapy, tomotherapy, and image guided radiation therapy (IGRT). Capability of determining the local tumor volume and location of the tumor has been significantly improved by applying single or multi-modality imaging fur static or dynamic target. The use of multi-modality imaging provides a more reliable tumor volume, eventually leading to a better definitive local control. Image registration technique is essential to fuse two different image modalities and has been In significant improvement. Imaging equipments and their common applications that are in active use and/or under development in radiation therapy are reviewed.

• 척추신경추나의학회지
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• 제8권2호
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• pp.39-46
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• 2013

Objectives : To identify the association between cross-sectional area of lumbar regional muscle and stability(ST), center of pressure(COP) assessed by tetrax. Methods : Patients(n=55) who had taken L-SPINE MRI and Tetrax(Sunlight, Israel) were analyzed retrospectively. To evaluate the cross-sectional area of lumbar regional muscle, L-SPINE MRI was used. Data of ST, COP were accumulated by using dynamic equilibrium analysis by Tetrax. Of the lumbar regional muscles, the Psoas muscles and the Paraspinalis muscles were examined. Using Pearson correlation, we analyzed COP, ST and the difference between the cross-sectional area of lumbar regional muscles. Results : The variance of cross-sectional area of both sides of Psoas muscle and COP had moderate positive correlation(r=0.621). Between variance of cross-sectional area of both sides of Paraspinalis and lumbar regional muscle and COP there was low positive correlation(r=0.287, r=0.329) ST also had low correlation with variance of cross-sectional area of both sides of Psoas muscle. Conclusion : The variance of cross-sectional area between both sides of Psoas muscle had moderate correlation with COP.

• Investigative Magnetic Resonance Imaging
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• 제12권2호
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• pp.142-147
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• 2008

목적 : 본 연구는 핵자기공명 분광기를 개조한 미세영상 기법을 이용하여, 동물실험에 주류를 이루는 mouse를 대상으로, 0.1 mm 이내의 초고해상도 자기공명영상을 5분 정도 시간 안에 획득할 수 있는 방법을 개발하고자 하였다. 대상 및 방법 : 사용된 mouse는 C57BL/6로서 무게 50 그램 이내의 mouse를 사용하였다. 본 연구에 활용된 초전도 자석은 구경 89 mm, 4.7 T의 자기장 세기를 가진 수직형 자석이며, 사용된 샘플 코일의 직경은 30 mm 이고, 사용된 펄스시퀀스는 fast spin echo (FSE) 및 gradient echo (GE) 기법들이다. 결과 : 최적의 자기공명영상 파라미터를 확보하면서 2차원 영상으로서 수소밀도 및 T2 강조 영상을 획득하였다. 영상으로부터 mouse 뇌의 미세부분까지 상세히 해부학적 구조를 확인할 수 있었고, 또한 입체적인 정보를 획득하기 위하여 3D 영상도 부가적으로 획득하였다. 조영제를 이용한 dynamic contrast 연구에 3D 영상이 매우 유용하였다. 결론 : 본 연구를 통하여 mouse 뇌에 대한 고해상도 자기공명영상 획득을 위한 최적의 파라미터를 확보할 수 있었고, 또한 성공적인 자기공명영상도 획득하였다. 즉, 사람이나 다른 소동물뇌의 경우와 같이 mouse 뇌 조직의 다양한 부위의 미세부분을 확인할 수 있는 충분한 고해상도의 영상을 획득하였다. 최근 국내에서 mouse를 이용한 자기공명영상 연구가 시작되었으나 아직 초기단계라고 평가할 수 있고, mouse는 다른 동물에 비하여 취급/관리하기 쉬우므로 향후 mouse를 이용한 뇌 연구가 활성화 될 것으로 사료된다.

• Korean Journal of Radiology
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• 제24권7호
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• pp.647-659
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• 2023

Objective: The study was conducted to investigate the effect of correct occlusion of the left atrial appendage (LAA) on intracardiac blood flow and thrombus formation in patients with atrial fibrillation (AF) using four-dimensional (4D) flow magnetic resonance imaging (MRI) and three-dimensional (3D)-printed phantoms. Materials and Methods: Three life-sized 3D-printed left atrium (LA) phantoms, including a pre-occlusion (i.e., before the occlusion procedure) model and correctly and incorrectly occluded post-procedural models, were constructed based on cardiac computed tomography images from an 86-year-old male with long-standing persistent AF. A custom-made closed-loop flow circuit was set up, and pulsatile simulated pulmonary venous flow was delivered by a pump. 4D flow MRI was performed using a 3T scanner, and the images were analyzed using MATLAB-based software (R2020b; Mathworks). Flow metrics associated with blood stasis and thrombogenicity, such as the volume of stasis defined by the velocity threshold ($\left|\vec{V}\right|$ < 3 cm/s), surface-and-time-averaged wall shear stress (WSS), and endothelial cell activation potential (ECAP), were analyzed and compared among the three LA phantom models. Results: Different spatial distributions, orientations, and magnitudes of LA flow were directly visualized within the three LA phantoms using 4D flow MRI. The time-averaged volume and its ratio to the corresponding entire volume of LA flow stasis were consistently reduced in the correctly occluded model (70.82 mL and 39.0%, respectively), followed by the incorrectly occluded (73.17 mL and 39.0%, respectively) and pre-occlusion (79.11 mL and 39.7%, respectively) models. The surfaceand-time-averaged WSS and ECAP were also lowest in the correctly occluded model (0.048 Pa and 4.004 Pa^-1, respectively), followed by the incorrectly occluded (0.059 Pa and 4.792 Pa^-1, respectively) and pre-occlusion (0.072 Pa and 5.861 Pa^-1, respectively) models. Conclusion: These findings suggest that a correctly occluded LAA leads to the greatest reduction in LA flow stasis and thrombogenicity, presenting a tentative procedural goal to maximize clinical benefits in patients with AF.

• Investigative Magnetic Resonance Imaging
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• 제1권1호
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• pp.130-134
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• 1997

목적: 역동적 자기공명영상에서 위암의 조영증강양상을 분석하여, 병변의 평가에 조영증강검사의 필요성을 규명하고자 하였다. 대상 및 방법: 병리조직학적으로 증명된 12명의 환자를 대상으로 하였다. 1.0T 자기공명영상장치를 이용하였고, FLASH T1 강조영상기법으로 조영제 주입전, 30초 후, 60초 후, 90초 후에 각각 횡단스캔을 얻었다. 검사 전 환자에게 1리터의 물을 마시게 하였고 장진경제인 Buscopan을 근육주사 하였다. 각 시기에서 병변의 신호 대 잡음비를 측정하였고, 병변과 췌장, 병변과 위장내 물과의 신호차이 대 잡음비를 측정하였다. 또한 각 시기의 영상에서 병변의 두으러짐을 0-3등급으로 나누어 두 명의 방사선과 의사가 합의하에 평가하였다. 결과: 병변의 신호 대 잡음비는 조영증강 전, 조영증강 후 30초, 60초, 90초의 시간경과에 따라 점차 증가하였다(38.7,42.5,57.4,65.7). 병변과 췌장과의 신호차이 대 잡음비는 10.5, 9.33, 9.99, 10.66으로 유의하게 증가하였다. 병변과 위장내 물과의 신호차이 대 잡음비도 1.24, 25.01, 39.30, 45.89로 유의하게 증가하였다. 그러나 정성적 분석에서는 조영 전 영상이 조영 후 영상에 비하여 병변의 두드러짐이 컸다(평균등급:2.8, 1.8, 1.6, 1.5). 병변의 신호강도는 조영증강 후 90초 지연영상에서 가장 높은 신호강도를 보여 병변의 위강쪽은 뚜렷하게 보였다. 그러나 병변과 위 주위 지방조직의 신호강도 차이가 줄어들어 전체적으로는 조영증강 전 영상에서 조영증강 후 영상보다 병변이 분명하게 보였다. 결론: 위암의 역동적 자기공명영상의 조영 전 영상에서 조영 후 영상보다 병변이 분명하게 보이므로 조영증강은 필요 없다고 생각된다.

• Investigative Magnetic Resonance Imaging
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• 제22권2호
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• pp.102-109
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• 2018

Purpose: The purpose of this study is to compare the performance of the T1 3D subtraction technique and the conventional 2D dynamic contrast enhancement (DCE) technique in diagnosing Cushing's disease. Materials and Methods: Twelve patients with clinically and biochemically proven Cushing's disease were included in the study. In addition, 23 patients with a Rathke's cleft cyst (RCC) diagnosed on an MRI with normal pituitary hormone levels were included as a control, to prevent non-blinded positive results. Postcontrast T1 3D fast spin echo (FSE) images were acquired after DCE images in 3T MRI and image subtraction of pre- and postcontrast T1 3D FSE images were performed. Inter-observer agreement, interpretation time, multiobserver receiver operating characteristic (ROC), and net benefit analyses were performed to compare 2D DCE and T1 3D subtraction techniques. Results: Inter-observer agreement for a visual scale of contrast enhancement was poor in DCE (${\kappa}=0.57$) and good in T1 3D subtraction images (${\kappa}=0.75$). The time taken for determining contrast-enhancement in pituitary lesions was significantly shorter in the T1 3D subtraction images compared to the DCE sequence (P < 0.05). ROC values demonstrated increased reader confidence range with T1 3D subtraction images (95% confidence interval [CI]: 0.94-1.00) compared with DCE (95% CI: 0.70-0.92) (P < 0.01). The net benefit effect of T1 3D subtraction images over DCE was 0.34 (95% CI: 0.12-0.56). For Cushing's disease, both reviewers misclassified one case as a nonenhancing lesion on the DCE images, while no cases were misclassified on T1 3D subtraction images. Conclusion: The T1 3D subtraction technique shows superior performance for determining the presence of enhancement on pituitary lesions compared with conventional DCE techniques, which may aid in diagnosing Cushing's disease.

• Korean Journal of Radiology
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• 제22권7호
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• pp.1152-1162
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• 2021

Objective: This study aimed to determine whether there are regional differences in the blood-brain barrier (BBB) permeability of cognitively normal elderly participants and to identify factors influencing BBB permeability with a clinically feasible, 10-minute dynamic contrast-enhanced (DCE) MRI protocol. Materials and Methods: This IRB-approved prospective study recruited 35 cognitively normal adults (26 women; mean age, 64.5 ± 5.6 years) who underwent DCE T1-weighted imaging. Permeability maps (K_trans) were coregistered with masks to calculate the mean regional values. The paired t test and Friedman test were used to compare Ktrans between different regions. The relationships between K_trans and the factors of age, sex, education, cognition score, vascular risk burden, vascular factors on imaging, and medial temporal lobar atrophy were assessed using Pearson correlation and the Spearman rank test. Results: The mean permeability rates of the right and left hippocampi, as assessed with automatic segmentation, were 0.529 ± 0.472 and 0.585 ± 0.515 (K_trans, x 10^-3 min^-1), respectively. Concerning the deep gray matter, the K_trans of the thalamus was significantly greater than those of the putamen and hippocampus (p = 0.007, p = 0.041). Regarding the white matter, the K_trans value of the occipital white matter was significantly greater than those of the frontal, cingulate, and temporal white matter (p < 0.0001, p = 0.0007, p = 0.0002). The variations in K_trans across brain regions were not related to age, cognitive score, vascular risk burden, vascular risk factors on imaging, or medial temporal lobar atrophy in the study group. Conclusion: Our study demonstrated regional differences in BBB permeability (K_trans) in cognitively normal elderly adults using a clinically acceptable 10-minutes DCE imaging protocol. The regional differences suggest that the integrity of the BBB varies across the brains of cognitively normal elderly adults. We recommend considering regional differences in K_trans values when evaluating BBB permeability in patients with neurodegenerative diseases.

• Investigative Magnetic Resonance Imaging
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• 제13권2호
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• pp.183-189
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• 2009

목적 : 유방자기공명영상에서 3 차원 최대 강도 투사 (3D MIP) 재건 영상의 유용성을 알아보고자 하였다. 대상 및 방법 : 유방암으로 진단받고 유방자기공명영상을 시행한 27명의 환자의 54개의 유방을 대상으로 하였다. GE Signa Excite Twin speed (GE medical system, Wisconsin, USA) 1.5 T 기기를 이용하여 기본 영상으로 축면 T2 강조 T1 강조 영상과 시상면 T1 강조 지방 억제 영상, 역동적 조영 증강 영상과 감산 영상을 얻었다. 이후 초기 역동적 조영증강 영상의 감산영상으로 워크스테이견 (GE Medical system)을 이용하여 3D MIP 영상을 얻었다. 3D MIP 영상과 기본 유방자기공명영상에서 발견된 병변을 ACR BI-$RADS^{(R)}$ MRI lexicon에 따라 분석하였다. 각각의 영상에서 발견된 병변의 소견들을 비교하고 3D MIP에서 기본자기공명영상에서 보다 추가적인 정보를 얻을 수 있는지 알아보았다. 결과 : 종괴의 경우 기본 유방자기공명영상에서 보이는 56개 중 43개가 3D MIP 영상에서 발견되었다 (76.8%). 비종괴성 조영 증강의 경우 20개 중 17개가 발견되었다 (85%). 169개의 초점성 조영증강 병변이 3D MIP 영상에서, 109개가 기본 유방자기공명영상에서 확인되었다. 3D MIP 영상에서 60.9%의 category 3병변이 발견되었고(14/23), 68.87%의 category 4 병변 (11/16), 100%의 category 5병변 (28/28)이 발견되었다. 3D MIP 영상에서 분석된 조영증강 병변들의 category가 기본 유방 자기공명 영상의 결과들과 통계적으로 일치하였다(p-value < 0.0001). 기본 유방 자기공명 영상에서 초점으로 분석된 2개의 병변들이 3D MIP 영상에서는 다초점성의 악성 병변으로 발견되었고, 1개의 추가적 병변이 3D MIP 영상에서만 발견되었다. 결론 : 3D MIP 영상은 한계점들을 갖고 있으나, 기본 유방자기공명영상의 분석에 있어 추가적으로 이용 시 유용하다.