• Investigative Magnetic Resonance Imaging
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• v.26 no.1
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• pp.32-42
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• 2022

Purpose: To evaluate the clinical benefit of 2D contrast-enhanced T2 fluid-attenuated inversion recovery (CE-T2 FLAIR) image for detecting leptomeningeal metastasis (LM) in the brain metastasis work-up for lung cancer. Materials and Methods: From June 2017 to July 2019, we collected all consecutive patients with lung cancer who underwent brain magnetic resonance image (MRI), including contrast-enhanced 3D fast spin echo T1 black-blood image (CE-T1WI) and CE-T2 FLAIR; we recruited clinico-radiologically suspected LM cases. Two independent readers analyzed the images for LM in three sessions: CE-T1WI, CE-T2 FLAIR, and their combination. Results: We recruited 526 patients with suspected lung cancer who underwent brain MRI; of these, we excluded 77 (insufficient image protocol, unclear pathology, different contrast media, poor image quality). Of the 449 patients, 34 were clinico-radiologically suspected to have LM; among them, 23 were diagnosed with true LM. The calculated detection performance of CE-T1WI, CE-T2 FLAIR, and combined analysis obtained from the 34 suspected LM were highest in the combined analysis (AUC: 0.80, 0.82, and 0.89, respectively). The inter-observer agreement was also the highest in the combined analysis (0.68, 0.72, and 0.86, respectively). In quantitative analyses, CNR of CE-T2 FLAIR was significantly higher than that of CE-T1WI (Wilcoxon signed rank test, P < 0.05). Conclusion: Adding CE-T2 FLAIR might provide better detection for LM in the brain-metastasis screening for lung cancer.

• Investigative Magnetic Resonance Imaging
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• v.20 no.4
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• pp.215-223
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• 2016

Purpose: The management of metal-induced field inhomogeneities is one of the major concerns of distortion-free magnetic resonance images near metallic implants. The recently proposed method called "Slice Encoding for Metal Artifact Correction (SEMAC)" is an effective spin echo pulse sequence of magnetic resonance imaging (MRI) near metallic implants. However, as SEMAC uses the noisy resolved data elements, SEMAC images can have a major problem for improving the signal-to-noise ratio (SNR) without compromising the correction of metal artifacts. To address that issue, this paper presents a novel reconstruction technique for providing an improvement of the SNR in SEMAC images without sacrificing the correction of metal artifacts. Materials and Methods: Low-rank approximation in each coil image is first performed to suppress the noise in the slice direction, because the signal is highly correlated between SEMAC-encoded slices. Secondly, SEMAC images are reconstructed by the best linear unbiased estimator (BLUE), also known as Gauss-Markov or weighted least squares. Noise levels and correlation in the receiver channels are considered for the sake of SNR optimization. To this end, since distorted excitation profiles are sparse, $l_1$ minimization performs well in recovering the sparse distorted excitation profiles and the sparse modeling of our approach offers excellent correction of metal-induced distortions. Results: Three images reconstructed using SEMAC, SEMAC with the conventional two-step noise reduction, and the proposed image denoising for metal MRI exploiting sparsity and low rank approximation algorithm were compared. The proposed algorithm outperformed two methods and produced 119% SNR better than SEMAC and 89% SNR better than SEMAC with the conventional two-step noise reduction. Conclusion: We successfully demonstrated that the proposed, novel algorithm for SEMAC, if compared with conventional de-noising methods, substantially improves SNR and reduces artifacts.

• Journal of Korean Neurosurgical Society
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• v.39 no.3
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• pp.210-214
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• 2006

Objective : We investigate risk factors of cerebral microbleeds[MBs] and their relation to concomitant magnetic resonance[MR] findings in intracerebral hemorrhages[ICHs] patients. Methods : We studied 100 consecutive patients with primary ICH over a 1-year period. These patients underwent brain MR images using 3.0-T scanners within the first week of the hemorrhage. MBs and old hematomas were located and counted by using $T2^*-weighted$ gradient-echo MR imaging. We also counted lacunes and graded white matter and periventricular hyperintensity on T1- and T2-weighted spin-echo sequences. The association between MBs and vascular risk factors and MR abnormalities were analyzed. Results : MBs were seen in 77 of ICH patients, and their number ranged from 1 to 65 lesions [mean 11, median 6]. The locations of MBs were subcortex-cortex [40.6%], basal ganglia [26.7%], thalamus [14.1 %], brain stem [12.5%], and cerebellum [9.1 %]. Analysis of clinical data revealed that age, hypertension, history of stroke, and duration of hypertension were frequently associated with MBs. The incidence of lacunes, old hematomas, and advanced leukoaraiosis was significantly higher in the MBs group, compared with the patients without MBs. Conclusion : MBs are frequently observed in ICH patients with advancing age, chronic hypertension, and previous hemorrhagic stroke, and are also closely related with morphological signs of occlusive type microangiopathy, such as lacunar infarct and severe leukoaraiosis.

• Investigative Magnetic Resonance Imaging
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• v.20 no.1
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• pp.44-52
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• 2016

Purpose: To quantitatively and qualitatively compare fat-suppressed MRI quality using iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) with that using frequency selective fat-suppression (FSFS) T2- and postcontrast T1-weighted fast spin-echo images of the head and neck at 3T. Materials and Methods: The study was approved by our Institutional Review Board. Prospective MR image analysis was performed in 36 individuals at a single-center. Axial fat suppressed T2- and postcontrast T1-weighted images with IDEAL and FSFS were compared. Visual assessment was performed by two independent readers with respect to; 1) metallic artifacts around oral cavity, 2) susceptibility artifacts around upper airway, paranasal sinus, and head-neck junction, 3) homogeneity of fat suppression, 4) image sharpness, 5) tissue contrast of pathologies and lymph nodes. The signal-to-noise ratios (SNR) for each image sequence were assessed. Results: Both IDEAL fat suppressed T2- and T1-weighted images significantly reduced artifacts around airway, paranasal sinus, and head-neck junction, and significantly improved homogeneous fat suppression in compared to those using FSFS (P < 0.05 for all). IDEAL significantly decreased artifacts around oral cavity on T2-weighted images (P < 0.05, respectively) and improved sharpness, lesion-to-tissue, and lymph node-to-tissue contrast on T1-weighted images (P < 0.05 for all). The mean SNRs were significantly improved on both T1- and T2-weighted IDEAL images (P < 0.05 for all). Conclusion: IDEAL technique improves image quality in the head and neck by reducing artifacts with homogeneous fat suppression, while maintaining a high SNR.

• Journal of Magnetics
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• v.22 no.1
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• pp.146-149
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• 2017

In this study, we compared the standardized value of each signal intensity, the apparent diffusion coefficient (ADC) that digitizes the diffusion of water molecules, and the signal to noise ratio (SNR) using b value 0 400, 1400 ($s/mm^2$). From March 2013 to December 2013, patients with suspicion of simple compound fracture and metastatic spine cancer were included in the MR readout. We used a 1.5 Tesla Achieva MRI system and a Syn-Spine Coil. Sequence is a DWI SE-EPI sagittal (diffusion weighted imaging spin echo-echo planar imaging sagittal) image with b-factor ($s/mm^2$) 0, 400, 1400 were used. Data analysis showed ROI (Region of Interest) in diseased area with high SI (signal intensity) in diffusion-weighted image b value 0 ($s/mm^2$) Using the MRIcro program, each SI was calculated with images of b-value 0, 400, and 1400 ($s/mm^2$), ADC map was obtained using Metlab Software with each image of b-value, The ADC is obtained by applying the ROI to the same position. The standardized values ($SI_{400}/SI_0$, $SI_{400}/SI_0$) of simple compression fractures were $0.47{\pm}0.04$ and $0.23{\pm}0.03$ and the standardized values ($SI_{400}/SI_0$, $SI_{400}/SI_0$) of the metastatic spine were $0.57{\pm}0.07$ and $0.32{\pm}0.08$ And the standardized values of the two diseases were statistically significant (p < 0.05). The ADC ($mm^2/s$) for b value 400 ($s/mm^2$) and 1400 ($s/mm^2$) of the simple compression fracture disease site were $1.70{\pm}0.16$ and $0.93{\pm}0.28$ and $1.24{\pm}0.21$ and $0.80{\pm}0.15$ for the metastatic spine. The ADC ($mm^2/s$) for b value 400($s/mm^2$) was statistically significant (p < 0.05) but the ADC ($mm^2/s$) for b value 1400 (p > 0.05). In conclusion, multi - b value recognition of signal changes in diffusion - weighted imaging is very important for the diagnosis of various spinal diseases.

• Journal of the Korean Society of Radiology
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• v.17 no.7
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• pp.1115-1122
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• 2023

This study aimed to present reasonable reception bandwidth application standards for the purpose of suppressing metal objects during MRI examinations. For this purpose, T2 contrast images were acquired using high-speed spin echo technology on a phantom made of screws for spinal surgery, and metal objects were detected. In addition, images were obtained by increasing the reception bandwidth from 100 Hz/PX to 800 Hz/PX by 100 Hz/PX. The metal artifacts were determined as the sum of the areas of the signal attenuation area and the signal accumulation area. In addition, Pearson correlation analysis was performed to analyze the pattern of metal artifacts according to imaging variables. As a result, the signal accumulation area did not change significantly as the reception bandwidth increased (p>0.05), but the signal loss area and the area of metal artifacts decreased as the reception bandwidth increased (p<0.05). Interestingly, the area of metal objects decreased to a maximum in the section where the reception bandwidth was increased from 100 Hz/PX to 200 Hz/PX, consistent with the section where the echo spacing was reduced to a maximum due to the increase in reception bandwidth. In addition, the correlation analysis results also showed that the eco spacing was more related to the signal attenuation area and the area of metal objects than to the reception bandwidth. Therefore, if the reception bandwidth is increased for the purpose of reducing metal objects, it is reasonable to set it based on a value that minimizes the echo spacing in consideration of image quality factors.

• Proceedings of the KOSOMBE Conference
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• v.1997 no.11
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• pp.555-558
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• 1997

A new approach to silent MR imaging using a rotating DC gradient has been explored and experimentally studied. As is known, acoustic or sound noise has been one of the major problems in handling patients, mainly due to the fast gradient pulsings in interaction with the main magnetic field. The sound noise is also proportionally louder as the magnetic field strength becomes larger. In this article, we have described a new imaging technique using a mechanically rotating DC gradient coil as an approach toward silent MR imaging, i.e., a mechanically rotated DC gradient effectively replaces both the phase encoding as well as the readout gradient pulsings and data obtained in this manner provides a set of project ion data which later can be used or the projection reconstructionorwithsomeinterpolation techniques one can also perform conventional 2-D FFT (Fast Fourier Transform) image reconstruction. We found, with this new technique, that the sound noise intensity compared with the conventional imaging technique, such as spin echo sequence, is reduced down to -20.7 dB or about 117.5 times. The experimental pulse sequence and its principle are described and images obtained by the new silent MR imaging technique are reported.

• Journal of Magnetics
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• v.21 no.1
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• pp.148-152
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• 2016

The main goal was to evaluate effectiveness of a modified TSE sequence compared with DIR (double inversion recovery) sequence in acquisition of fast flow brain vessel images using signal void effect. 32 healthy volunteers (10 men and 22 women; mean age of 31 years; ranging between 28-43 years) who underwent black blood DIR sequence (group A) and the modified TSE sequence (group B) were enrolled in our study. Signal to Noise Ratio (SNR) and Contrast to Noise Ratio (CNR) of the internal carotid arteries' lumen were compared in T1 and T2 weighted images for both group A and B. The images obtained from group B showed lower SNR values in internal carotid artery than the group A in both of the T1 and T2 weighted images (11.49% and 13.66% respectively). While the CNR values were higher in the group B than the group A in both of the T1 and T2 weighted images (8.69% and 7.55 % respectively). The qualitative score of all categories were not significantly different between the two groups. Furthermore approximately 49% of the total scan time was reduced from group B. Our study is to shorten the scanning time and minimize the inconveniences of the patients in acquisition of the black blood images of brain by using the signal void effect in the modified TSE technique while keeping the diagnostic value of the test.

• Proceedings of the KSMRM Conference
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• 2002.11a
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• pp.78-78
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• 2002

Purpose： The purpose of this study is to describe a distributed circuit approach to high frequency volume coil design illustrated with specific coils built accordingly and results obtained from animal studies at 3.0 tesla. Method： All experiments were conducted on 3T MRI system (Medinus Co., Ltd. Korea). The tuned TEM resonator measures 15cm outer diameter. by 10cm inside diameter by 30cm in length. The inside diameter and length were determined by animals body or head size (eg. rats or small dogs, etc.) while the outer diameter was chosen for compactness with some sacrifice of the optimal coil Q predicted for a larger cavity. A spin echo sequence with a TR/TE/flip angle=500/12.4ms/$75^{\circ}$was used to check image qualities with phantom. The breed of rat which used for animal images was Sprague-dawley(SD) and was anesthetic using ketamin hydrochloride 75mg/kg.

• Progress in Medical Physics
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• v.15 no.1
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• pp.54-58
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• 2004

The aim of this study was to develop special birdcage resonators for small objects including the human wrist, hand and small animals, using 3T MRI/MRS. Before substantial development, different types of parameters were arranged, based on theoretical analysis, through lumped element transmission line theory. The primary analysis was peformed with a network analyzer (HP 4195A) and the final experimental analysis was carried out with 3T MRI (Medinus, Korea). The manufactured birdcage resonator is typically composed of 12-element structures to which a low-pass filter is fundamentally applied. The diameter and length of each element of the birdcage resonator were as follows: (1) diameter 12 cm, length of element 22 cm, (2) diameter 15 cm, length of element 22 cm, and (2) diameter 17 cm, length of element 25 cm. Copper tape with a width of 1 cm was used for the coils. MRI acquisition parameters were TR=500 ms, TE=17 ms, and Ave=2 for T1-WT images, and TR=4,000 ms, TE=96 ms, and Ave=2 for T2-WT images. The ratio of the samples diameter to the birdcage resonators diameter was approximately 55%, 63% and 70%, respectively, for the three elements. This study determined that the best image quality and S/N ratio were obtained when the ratio of the object's diameter was approximately 50∼80%. A general theoretical analysis of the birdcage coil differs in many respects from the experimental results which were influenced by many factors that were not considering when the general theoretical analysis of the birdcage coil was peformed. The induced resistance may be considered as part of the resistive loss if the quantitative value can be determined using a radiation resistance approach.