• Korean Journal of Metals and Materials
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• v.50 no.7
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• pp.487-493
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• 2012

To analyze the factors on stretch-flangeability for 980 MPa-grade hot-rolled steels, two types of steels (Fe-Cr and Fe-Mo) were manufactured by hot-rolling. Manufactured steels at the low coiling temperature, such as 400 and $500^{\circ}C$, had poor stretch-flangeability due to un-uniformly distributed carbides and a large deviation of interphase hardness. However, when the coiling temperature was set at $650^{\circ}C$ with Fe-Cr steel, 998 MPa of ultimate tensile strength, 19% of total elongation and 65% of the hole expanding ratio were achieved by microstructural constituents of polygonal ferrite (PF) and granular ferrite (GF) dispersed with fine carbides (<50 nm). Therefore, the material to attain 980 MPa with superior formability was the Fe-Cr steel that was precipitation-hardened in polygonal ferrite and granular ferrite at the coiling temperature $650^{\circ}C$.

• Journal of Korean Neurosurgical Society
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• v.65 no.4
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• pp.523-530
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• 2022

Objective : To evaluate the safety and efficacy of an overlapped stenting-assisted coiling technique in treating vertebral artery dissecting aneurysm (VADA) via Low-profile Visualized Intraluminal Support (LVIS) stent-within-Neuroform EZ stent. Methods : From January 2017 to June 2019, 18 consecutive patients with VADAs (ruptured : unruptured=5 : 13) were treated with the overlapping stents assisted-coiling technique in our center. The overlapping manner was a Neuroform EZ stent being deployed first, followed by LVIS stents placement using the 'shelf' technique. The patients' clinical characteristics, technical feasibility and safety, and immediate and follow-up angiographic results were retrospectively reviewed. Results : Seventeen (94.4%) procedures were technically successful with an exact deployment of the stents and patent parent or perforator arteries. The immediate angiographies after procedure confirmed Raymond class I, II, and III occlusion of VADAs were in 12 (66.7%), two (11.1%), and four cases (22.2%), respectively. Post-procedural complications developed in one patient (5.6%) with minor brainstem infarctions, which resulted from an in-stent thrombosis during the procedure. Angiographic follow-up at 5.7 months (range 3 to 9 months) demonstrated Raymond class I and II occlusion were in all cases (100%). The modified Rankin Scale scores at 21.3 months (range 15 to 42 months) 0-2 in 17 cases (94.4%) and three in one case (5.6%). Conclusion : Overlapping stents via LVIS stent-within-Neuroform EZ stent combined with coiling is safe and effective for patients with VADA in the midterm results.

• Journal of Korean Neurosurgical Society
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• v.48 no.1
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• pp.53-58
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• 2010

Objective : The purpose of this study was to review the safety and durability of aneurysms treated with stent-assisted coiling of ruptured anterior communicating artery aneurysms with small parent vessels (< 2.0 mm). Methods : Retrospective review of all ruptured aneurysm treated with stent assisted endovascular coiling between March 2005 and March 2009 at our institution was conducted. We report 11 cases of the Neuroform stent placement into cerebral vessels measuring less than 2.0 mm in diameter (range, 1.3-1.9 mm) in anterior cerebral artery. Clinical follow-up ranged from 3 to 12 months and imaging follow-up was performed with cerebral angiography at 6 months and 12 months after discharge. Results : Complete occlusion was achieved in 10 patients, and a remnant neck was evident in one. No stent displacement or no dislodgement occurred during stent placement. There was no evidence of thromboembolic complication, arterial dissection and spasm during procedure. We performed follow-up angiography in all patients at 6 months and/or 12 months from the first procedure. The follow-up angiographic data showed successfully results except one in-stent stenosis case. All patients improved clinical performances except one patient with severe vasospasm who showed poor clinical condition initially. Conclusion : We have safely and successfully treated 11 vessels smaller than 2.0 mm in diameter with self-expanding stents with good short and intermediate term results. More clinical data with longer follow-ups are needed to establish the role of stent-assisted coiling in ruptured aneurysms with small parent vessels.

• Journal of Korean Neurosurgical Society
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• v.61 no.5
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• pp.653-659
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• 2018

Objective : Surgical obliteration of ruptured aneurysm of the proximal posterior inferior cerebellar artery (PICA) is challenging because of limited surgical accessibility. In recent years, coil embolization is the first-choice treatment for these lesions. However, coil embolization is not always easy in ruptured PICA aneurysm owing to the variable anatomical diversity of its shapes, its relationship to the parent artery, its low incidence, and accordingly, lesser neurointerventionist experience. Methods : The parent artery and microcatheter for easier navigation and the embolization technique for stable coiling were identified. Results : This study aimed to identify the more appropriate approach route, microcatheter, and strategies for an easier and safer, and more durable coil embolization in the treatment of lesions in the proximal PICA. Conclusion : Coil embolization for aneurysmal subarachnoid hemorrhage due to a ruptured proximal PICA remains a challenge, but with the appropriate coiling plan, it can be treated successfully.

• Journal of Korean Neurosurgical Society
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• v.51 no.4
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• pp.222-226
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• 2012

The waffle-cone technique is a modified stent application technique, which involves protrusion of the distal portion of a stent into an aneurysm fundus to provide neck support for subsequent coiling. The authors report two cases of wide necked basilar bifurcation aneurysms, which were not amenable to stent assisted coiling, that were treated using the waffle-cone technique with a Solitaire AB stent. A 58-year-old woman presented with severe headache. Brain CT showed subarachnoid hemorrhage and angiography demonstrated a ruptured giant basilar bifurcation aneurysm with broad neck, which was treated with a Solitaire AB stent and coils using the waffle-cone technique. The second case involved an 81-year-old man, who presented with dizziness caused by brain stem infarction. Angiography also demonstrated a large basilar bifurcation unruptured aneurysm with broad neck. Solitaire AB stent deployment using the waffle-cone technique, followed by coiling resulted in near complete obliteration of aneurysm. The waffle-cone technique with a Solitaire AB stent can be a useful alternative to conventional stent application when it is difficult to catheterize bilateral posterior cerebral arteries in patients with a wide-necked basilar bifurcation aneurysm.

• Proceedings of the Korean Nuclear Society Conference
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• 1999.10a
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• pp.355.2-355
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• 1999

The spnng back phenomena occurring in the coiling process of a steam generator tube induces the dimensional inaccuracy and makes the coiling procedure difficult. In this research, an analytical model was developed to evaluate the amount of the spring back for SMART steam generator tubes. The model was developed on the basis of beam theory and elastic-perfectly plastic material property. This model was extended to consider the effect of plastic hardening and the effect of the tensile force on the spring back phenomena. Parametric studies were performed for various design variables of steam generator tubes in order to minimize the spring back in the design stage. A sensitivity analysis has shown that the low yield strength, the high elastic modulus, the small helix diameter, and the large tube diameter result in a small amount of the spring back. The amount of the spring back can be controlled by the selection of adequate design values in the basic design stage and reduced to an allowable limit by the application of the tensile force to the tube during the coiling process.rocess.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.111-113
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• 2007

The Mechanical properties of steel in hot strip mill were associated with the alloy composition, plastic deformation, cooling history and so on. In the case of the same alloy composition and deformation conditions, cooling history on ROT (run out table) is the main factor in affecting mechanical properties of steel, especially, in carbon steel. On ROT, the steel undergoes under various kinds of cooling conditions such as radiation, convection by air, water and wetting zone. The coiling temperature (CT) of the steel is also important factor in affecting mechanical properties. But with the same CT, the mechanical properties of steel can be different because the temperature history of cooling is more important factor than CT itself. In this study, we have studied the relations between temperature history and mechanical properties of steel and then the predicted mechanical properties have compared with the measured values.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.102-105
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• 2001

The spring back taking place after the coiling process of steam generator tube leads to the dimensional inaccuracy. In order to reduce the spring back, tension force was applied to the one end of the tube during forming. In this work, parametric study using FEM was performed to find the appropriate magnitude of tension force. The force that induces minimum suing back was found by simultaneously taking account of suing back amount, cross-sectional ovality, and thickness of the tube wall after deformation. In addition, stress relieving by heat treatment was also simulated as an alternative to the former method. The latter was found to be more effective under the given constraints.

• Journal of Ocean Engineering and Technology
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• v.17 no.2
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• pp.21-26
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• 2003

The reel-lay method of submarine pipelines a continuous string of pipe coiled onto a reel. Assembly of this pipe that is string is accomplished onshore by welding, and nondestructive testing is carried out prior to coiling the pipe. The total length of pipes on the reel depends on the reel and pipe diameters. Pipeline installation is accomplished by uncoiling, straightening the pipe, and laying out the pipe string onto the seabed as the barge moves forward. Installation associated with coiling and uncoiling is related to the bending moment and strain relationship of the pipeline, A highgrade pipe material is required when the reel-lay method is used. This paper is concerned with the highly plastic bending moment of the pipeline, including the effect of ovality. Moment calculation in the pipe is accomplished by the numerical method, including the variable ovalities during the plastic bending of the pipe string. The new calculation method of the high plastic bending moment was applied to the reel-lay method.

• Journal of Korean Neurosurgical Society
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• v.50 no.6
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• pp.517-519
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• 2011

Stent assisted coiling on intracranial broad neck aneurysm has been considered as an effective technique and has made the complex aneurysms amenable to coiling. However, stent navigation and application themselves often have the problems especially when the parent vessel angle (entrance between afferent and efferent vessel) is over 90 degrees. We report here a case of a ruptured broad neck basilar top aneurysm that was successfully coiled using two self-expandable stents (Enterprise and Neuroform) placed in a fashion of modified Y-configured stents with waffle cone technique.