• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.12
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• pp.587-591
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• 2001

This paper describes the general and efficient design method of an axial and a radial shim coils to correct field impurities of various harmonic orders in the imaging volume of Magnetic Resonance Imaging magnet. Shim coils are optimized by BCLSF subroutine of IMSL, which is the well-known commercial package for optimization, aiming at maximizing the magnitude of the desired field component as well as minimizing other field components. In order to evaluate their effect, the developed method was applied to the MRI magnet constructed in KERI.

• Investigative Magnetic Resonance Imaging
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• v.23 no.1
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• pp.1-16
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• 2019

Dynamic contrast enhanced (DCE) magnetic resonance (MR) imaging plays an important role in non-invasive detection and characterization of primary and metastatic lesions in the liver. Recently, efforts have been made to improve spatial and temporal resolution of DCE liver MRI for arterial phase imaging. Review of recent publications related to arterial phase imaging of the liver indicates that there exist primarily two approaches: breath-hold and free-breathing. For breath-hold imaging, acquiring multiple arterial phase images in a breath-hold is the preferred approach over conventional single-phase imaging. For free-breathing imaging, a combination of three-dimensional (3D) stack-of-stars golden-angle sampling and compressed sensing parallel imaging reconstruction is one of emerging techniques. Self-gating can be used to decrease respiratory motion artifact. This article introduces recent MRI technologies relevant to hepatic arterial phase imaging, including differential subsampling with Cartesian ordering (DISCO), golden-angle radial sparse parallel (GRASP), and X-D GRASP. This article also describes techniques related to dynamic 3D image reconstruction of the liver from golden-angle stack-of-stars data.

• Investigative Magnetic Resonance Imaging
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• v.23 no.4
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• pp.328-340
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• 2019

Purpose: To generate phase images with free of motion-induced artifact and susceptibility-induced distortion using 3D radial ultrashort TE (UTE) MRI. Materials and Methods: The field map was theoretically derived by solving Laplace's equation with appropriate boundary conditions, and used to simulate the image distortion in conventional spin-warp MRI. Manufacturer's 3D radial imaging sequence was modified to acquire maximum number of radial spokes in a given time, by removing the spoiler gradient and sampling during both rampup and rampdown gradient. Spoke direction randomly jumps so that a readout gradient acts as a spoiling gradient for the previous spoke. The custom raw data was reconstructed using a homemade image reconstruction software, which is programmed using Python language. The method was applied to a phantom and in-vivo human brain and abdomen. The performance of UTE was compared with 3D GRE for phase mapping. Local phase mapping was compared with T₂* mapping using UTE. Results: The phase map using UTE mimics true field-map, which was theoretically calculated, while that using 3D GRE revealed both motion-induced artifact and geometric distortion. Motion-free imaging is particularly crucial for application of phase mapping for abdomen MRI, which typically requires multiple breathold acquisitions. The air pockets, which are caught within the digestive pathway, induce spatially varying and large background field. T₂* map, that was calculated using UTE data, suffers from non-uniform T₂* value due to this background field, while does not appear in the local phase map of UTE data. Conclusion: Phase map generated using UTE mimicked the true field map even when non-zero susceptibility objects were present. Phase map generated by 3D GRE did not accurately mimic the true field map when non-zero susceptibility objects were present due to the significant field distortion as theoretically calculated. Nonetheless, UTE allows for phase maps to be free of susceptibility-induced distortion without the use of any post-processing protocols.

• Proceedings of the KOSOMBE Conference
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• v.1996 no.11
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• pp.161-164
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• 1996

An actively-shielded $r^{2}$-gradient coil has been developed for brain localized MRI or MRS. Spatial localization is very useful for spatial volume selection in MRI or MR Spectroscopy(MRS). The radial(or $R^{2}-$) gradient coil is useful in reducing the artifact or in improving the SNR by selecting the volume with less number of RF pulses. It is, however, difficult to implement the coil with a gradient intensity strong enough to use it for practical whole-body MRI system. For example, the smallest volume size for selection is just 6 cm in diameter with a 250 Ampere of current driving for a whole-body system (in case of 70-cm-diameter). In this study, an asymetric $r^{2}$-coil with a small diameter of 35 cm has been designed and implemented for brain localized MRI or MRS. An 8-rod high-pass-type birdcage RF coil has also been implemented. The coil set has been developed for 1.0 Tesla Medison MRI system and its performance has been verified experimentally.

• Archives of Reconstructive Microsurgery
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• v.21 no.2
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• pp.86-91
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• 2012

Purpose: Mass can compress around tissue and cause deviation of normal anatomical structures. Often, mass grows toward neurovascular pedicle and encircles depending on the nature of mature mass. Neglecting neurovascular involvement of the mass is a serious problem not to be overlooked. Authors have performed microscopic approach regarding mass involving the neurovascular pedicle in the hand. Materials and Methods: From January 2007 through February 2012, retrospective analysis for nine cases of mass involving neurovascular pedicles was done. Patients were evaluated preoperatively by ultrasonography or MRI and checked intraoperative finding. Masses were evaluated by site, preoperative evaluation, involved neurovascular pedicle, histopathologic diagnosis, complication, and recurrence. Results: The site of mass involving neurovascular pedicles was 4 cases on the wrist, 2 cases on the palm, 2 cases on the finger, 1 case on the hand dorsum. Involved neurovascular pedicles were 3 radial arteries and nerves, 3 proper digital arteries and nerves, 1 radial artery, 1 superficial branch of radial nerve, 1 common digital artery and nerve. The histopathologic diagnosis of mass were 3 ganglions, 2 giant cell tumors, 2 epidermal cysts, 1 fibroma, and 1 benign spindle tumor. There were 2 cases of recurrence and secondary excisions were performed. Conclusion: Neurovascular pedicle injury can lead to serious complication like sensory and motor disorders, distal part ischemia, and so on. In case of mass suspected neurovascular invasion, accurate preoperative evaluation such as ultrasonography or MRI is necessary. To prevent any neurovascular related complication during mass excision, delicate surgical technique using a microscope becomes essential.

• Korean Journal of Head & Neck Oncology
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• v.27 no.1
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• pp.27-31
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• 2011

Purpose : Anterolateral thigh and radial forearm flap is the most important fasciocutaneous flap widely used for reconstruction of tongue. One important purpose of flap is replacing the volume of tongue but still there is no data about the surface area and volume to be reconstructed after glossectomy. In this paper, surface area and volume is estimated from the 3-dimensionally reconstructed MRI images to see which flap is more ideal and to give the reference value for reconstruction. Materials and Methods : With coronal MRI image, tongue including only the intrinsic muscle is delineated in every section and reconstructed 3-dimensionally and calculated the volume and surface area to be reconstructed according to the degree of glossectomy. This volume and surface area was compared with the volume of anterolateral thigh and radial forearm flap. Results : The volume and surface area to be reconstructed in hemiglossectomy was $39.0{\pm}4.0cm^3$ and $31.8{\pm}2.7cm^2$ respectively. The average thickness of anterolateral thigh flap is $9.4{\pm}2.8mm$ and that of radial forearm is $3.8{\pm}1.0mm$. Comparing the curve of tongue surface area and volume with the volume of flap, the anterolateral thigh flap has more ideal volume to replace the defect. Conclusions : The surface area and volume requested for reconstruction could be suggested and the anterolateral thigh flap has more ideal volume for reconstruction of glossectomy defect.

• Journal of the Korean Arthroscopy Society
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• v.15 no.2
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• pp.108-112
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• 2011

Purpose: To evaluate the thickness of the posterior horn of the medial meniscus accompanying with degenerative radial tear. Materials and Methods: We retrospectively reviewed 170 cases which show degenerative meniscal tear with variable degree of meniscal degeneration from February 2000 to February 2010. All cases were older than 40 years and 57 cases were men and 113 cases were women. Mean age were 55-year-old. We grouped the cases into 3 categories. Group A were composed with cases which showed horizontal and radial tear in posterior horn of medial meniscus. Group B showed horizontal tear only and group C showed intrasubstance degeneration without meniscal tear. Results: The mean thickness of medial meniscus posterior horn in group A, B, C were 7. 44 mm, 6.52 mm, 6.04 mm respectively. Group A showed significant increase of the thickness of medial meniscus posterior horn than group B, C. Group B also showed significant increase of thickness than group C. The degree of meniscal degeneration was highest in group A, which showed significant higher meniscal degeneration than group B and C, and, group B showed higher degeneration than group C, however, there was no statistically difference between group A and B regarding the degree of meniscal degeneration. Conclusion: The thickness of medial meniscus posterior horn was increased when accompanied with radial tear, which may elicit pain caused by meniscal impingement.

• The Journal of the Korean bone and joint tumor society
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• v.13 no.1
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• pp.55-59
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• 2007

Synovial chondroma is an uncommon benign lesion characterized by metaplastic cartilage formation within the synovial connective tissue, usually intraarticular, commonly affects the knee, hip and elbow. We would like to present the case of a 65-year-old man suffering from synovial chondroma of the right elbow responsible for radial nerve entrapment neuropathy. This is a case of synovial chondroma of the right elbow in an 65-year-old man presenting with pain and restricted joint movement of the right elbow, loss of extension and sensation of the right thumb and wrist. Plain radiographs showed narrowing of elbow joint space, bony spur on the edge of the joint, and radio-opaque sclerotic change of subchondral area. MRI revealed $16{\times}12$ mm sized round mass on the radial head, homogenous low signal on T1WI, heterogenous high and low signal on T2WI. The patient underwent marginal excision of the mass, compressing the radial nerve. Diagnosis was confirmed by histologic examination.

• Archives of Plastic Surgery
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• v.35 no.2
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• pp.205-207
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• 2008

Purpose: Although muscle hernia has been well described in the lower-extremity, muscle hernias in the upper extremity are extremely rare. As with lower extremity muscle hernias, the forearm muscle hernia may result from forced exertion of strenuous activity or following blunt trauma. The objective of this paper is to report an extraordinary case of forearm muscle hernia after radial forearm sensory tendocutaneous free flap with references. Methods: A 58-year-old male patient received wide excision and radical neck dissection and lower lip reconstruction with radial forearm sensory tendocutaneous free flap for squamous cell cancer on the lower lip. 16 weeks after the operation, he complained of protruding mass on the forearm and the size was increasing. In postoperative 18 weeks, MRI showed herniation of flexor digitorum superficialis. For unaesthetic cause and preventing progress, the authors performed direct fascial closure and Mesh graft. Results: In 12 months after the surgery there was no recurrence and the patient remained symptom-free. Conclusion: Pain on extremity exertion and unaesthetic buldge of forearm due to forearm muscle hernia were the primary indications for surgery which consist of direct closure, fasciotomy, fascia lata onlay graft, fascia lata inlay graft, etc. The authors experienced uncommon forearm muscle hernia after radial forearm free flap and satisfying result of treatment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.12
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• pp.6284-6289
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• 2013

With the application of k-space trajectory in a different manner and analyzing the influence of noise and its direction, this study was conducted to obtain high-quality images with minimal influence of noise during an MRI examination for cerebrovascular disease, which has a low signal for imaging. To evaluate influence of the noise of different k-space trajectories, a linear Cartesian coordination trajectory and non-Cartesian coordination trajectory were applied to 38 people who had received a high-resolution MRI examination for the early detection of cerebrovascular disease. As a result, the non-Cartesian coordination trajectory showed a 43.32% lower signal of lumens in the internal carotid artery than a linear Cartesian coordination trajectory, and the noise level was also 50.19% lower in a non-Cartesian coordination trajectory. This result shows that noise occurs less in a non-Cartesian coordination trajectory than a linear Cartesian coordination trajectory, and a non-Cartesian coordination trajectory is more effective in low-signal and low-resolution MRI examination. Therefore, when performing high-resolution MRI examination with a low-signal cerebrovascular system, the use of non-Cartesian coordination k-space trajectory will minimize the influence of noise and provide good images.