• The Journal of the Acoustical Society of Korea
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• v.29 no.4
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• pp.270-277
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• 2010

In this paper, we proposed an algorithm that improves tone quality of noisy audio signals by using ICA(Independent Component Analysis) algorithm and perceptual filters. Many algorithms have been proposed to eliminate the noise from the audio signals, such as spectral subtraction method, perceptual filter, etc. The perceptual filter uses a noise that is acquired from silent ranges in the input signal. In this case, the improvement rate of tone quality decreases if the noise energy is changed by the environmental variation in a signal frame. But the proposed method estimates a noise that is changed at each frame using ICA algorithm. The estimated noise is applied to perceptual filter. To show the performance of the proposed algorithm, several tests are performed to various input signals. With the proposed algorithm, we could confirm the enhancement of tone quality in terms of segmental SNR (SSNR), noise-to-mask ratio (NMR) and Degradation Category Rating (DCR) test.

• Journal of Korean Neurosurgical Society
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• v.67 no.4
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• pp.431-441
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• 2024

Objective : Gamma Knife radiosurgery (GKRS) is an effective and noninvasive treatment for high-risk arteriovenous malformations (AVMs). Since differences in GKRS outcomes by nidus type are unknown, this study evaluated GKRS feasibility and safety in patients with brain AVMs. Methods : This single-center retrospective study included patients with AVM who underwent GKRS between 2008 and 2021. Patients were divided into compact- and diffuse-type groups according to nidus characteristics. We excluded patients who performed GKRS and did not follow-up evaluation with magnetic resonance imaging or digital subtraction angiography within 36 months from the study. We used univariate and multivariate analyses to characterize associations of nidus type with obliteration rate and GKRS-related complications. Results : We enrolled 154 patients (mean age, 32.14±17.17 years; mean post-GKRS follow-up, 52.10±33.67 months) of whom 131 (85.1%) had compact- and 23 (14.9%) diffuse-type nidus AVMs. Of all AVMs, 89 (57.8%) were unruptured, and 65 (42.2%) had ruptured. The mean Spetzler-Martin AVM grades were 2.03±0.95 and 3.39±1.23 for the compact- and diffuse-type groups, respectively (p<0.001). During the follow-up period, AVM-related hemorrhages occurred in four individuals (2.6%), three of whom had compact nidi. Substantial radiation-induced changes and cyst formation were observed in 21 (13.6%) and one patient (0.6%), respectively. The AVM complete obliteration rate was 46.1% across both groups. Post-GKRS complication and complete obliteration rates were not significantly different between nidus types. For diffuse-type nidus AVMs, larger AVM size and volume (p<0.001), lower radiation dose (p<0.001), eloquent area location (p=0.015), and higher Spetzler-Martin grade (p<0.001) were observed. Conclusion : GKRS is a safe and feasible treatment for brain AVMs characterized by both diffuse- and compact-type nidi.

• Journal of the Korean Society of Radiology
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• v.83 no.5
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• pp.1153-1159
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• 2022

Dolichoectasia is an uncommon disorder characterized by the presence of a dilated, elongated, and tortuous cerebral artery. Its main pathologic mechanism is the disruption of the internal elastic lamina. Risk factors for dolichoectasia are advanced age, chronic hypertension, and metabolic disease. It mainly involves the vertebrobasilar vasculature (or "posterior circulation"), but dolichoectasia can also be seen in the anterior circulation, particularly the anterior cerebral artery. There are no reported cases of dolichoectasia involving both anterior and posterior circulation in South Korea. Here we report an unusual case of dolichoectasia involving both anterior and posterior circulation in a young female without any underlying disease on the basis of prominent imaging findings.

• Korean Journal of Radiology
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• v.20 no.6
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• pp.985-996
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• 2019

Objective: To determine the correlation between cerebral blood flow (CBF) on arterial spin labeling (ASL) MRI and the degree of postoperative revascularization assessed on digital subtraction angiography in children with moyamoya disease (MMD). Materials and Methods: Twenty-one children (9 boys and 12 girls; mean age, 8.4 ± 3.6 years; age range, 3-16 years) with MMD who underwent both pseudocontinuous ASL MRI at 1.5T and catheter angiography before and after superficial temporal artery encephaloduroarteriosynangiosis were included in this retrospective study. The degree of revascularization in the middle cerebral artery (MCA) territory was evaluated on external carotid angiography and was graded on a 3-point scale. On ASL CBF maps, regions of interest were manually drawn over the MCA territory of the operated side at the level of the centrum semi-ovale and over the cerebellum. The normalized CBF (nCBF) was calculated by dividing the CBF of the MCA territory by the CBF of the cerebellum. Changes in nCBFs were calculated by subtracting the preoperative nCBF values from the postoperative nCBF values. The correlation between nCBF changes measured with ASL and the revascularization grade from direct angiography was evaluated. Results: The nCBF value on the operated side increased after the operation (p = 0.001). The higher the degree of revascularization, the greater the nCBF change was: poor revascularization (grade 1), -0.043 ± 0.212; fair revascularization (grade 2), 0.345 ± 0.176; good revascularization (grade 3), 0.453 ± 0.182 (p = 0.005, Jockheere-Terpstra test). The interobserver agreement was excellent for the measured CBF values of the three readers (0.91-0.97). Conclusion: The nCBF values of the MCA territory obtained from ASL MRI increased after the revascularization procedure in children with MMD, and the degree of nCBF change showed a significant correlation with the degree of collateral formation evaluated via catheter angiography.

• Journal of the Korean Society of Radiology
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• v.85 no.2
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• pp.270-296
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• 2024

Coronary CT angiography (CCTA) is recognized for its role as a gatekeeper for invasive coronary angiography in patients suspected of coronary artery disease because it can detect significant coronary stenosis with high accuracy. However, heavy plaque in the coronary artery makes it difficult to visualize the lumen, which can lead to errors in the interpretation of the CCTA results. This is primarily due to the limited spatial resolution of CT scanners, resulting in blooming artifacts caused by calcium. However, coronary stenosis with high calcium scores often requires evaluation using CCTA. Technological methods to overcome these limitations include the introduction of high-resolution CT scanners, the development of reconstruction techniques, and the subtraction technique. Methods to improve reading ability, such as the setting of appropriate window width and height, and evaluation of the position of calcified plaque and residual visibility of the lumen in cross-sectional images, are also recommended.

• Journal of the Korean Society of Radiology
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• v.83 no.1
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• pp.184-188
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• 2022

Persistent trigeminal artery (PTA) represent an unusual remnant of the fetal carotid-basilar anastomosis. Persistent trigeminal artery variant (PTAV) is a rare anastomosis between the internal carotid artery and cerebellar artery, without an interposing basilar artery segment. We report the case of 49-year-old female with an incidentally discovered, rare variation of PTA that directly terminated in the ipsilateral superior cerebellar artery. The variation was observed on CT angiography, digital subtraction angiography, and MR angiography. Additionally, we reviewed the embryogenesis of PTA and PTAV and discussed the clinical implications of this variation.

• Journal of Cerebrovascular and Endovascular Neurosurgery
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• v.25 no.1
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• pp.62-68
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• 2023

The treatment of complicated anterior cerebral artery aneurysms remains challenging. Here, the authors describe a case of ruptured complicated A3 aneurysm, which was treated with trapping and in-situ bypass. A 47-year-old man presented to the emergency department with severe headache and vomiting. Computed tomography illustrated acute intracerebral hemorrhage in the right frontal lobe. Digital subtraction angiography (DSA) confirmed a ruptured fusiform A3 aneurysm with lobulation and a daughter sac. Trapping of the ruptured fusiform A3 aneurysm and distal end-to-side A4 anastomosis was performed. DSA on postoperative day 7 showed mild vasospasm to the afferent artery. However, 2 months later, DSA demonstrated that the antegrade flow through the anastomosis site had recovered. Thus, surgeons should be aware of the possibility of postsurgical vasospasm of anastomosed arteries, especially in cases of ruptured aneurysms.

• Journal of Cerebrovascular and Endovascular Neurosurgery
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• v.25 no.1
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• pp.87-92
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• 2023

Moyamoya disease (MMD) is a rare progressive steno-occlusive cerebrovascular disorder. Currently, revascularization surgery is used as optimal treatment to overcome MMD. However, revascularization for MMD has reported several complications. Also, iatrogenic complications such as pseudoaneurysms formation or dural arteriovenous fistulas (dAVFs) formation-has been identified in rare cases after the surgical intervention for revascularizations. We describe two cases. In first case, the patency of the anastomosis site was good and saccular type pseudoaneurysm formation was found at parietal branch of posterior middle meningeal artery (MMA) in transfemoral cerebral angiography (TFCA) performed on the twelfth day after surgery. We decided to treat pseudoaneurysm by endovascular embolization the next day, but the patient was shown unconsciousness and anisocoria during sleep at that day. Computed tomography showed massive subdural hemorrhage at the ipsilateral side, thus we performed decompressive craniectomy and hematoma evacuation. In second case, the patency of the anastomosis site was good and dAVF formation at right MMA was found in TFCA performed on the sixth day after surgery. We performed endovascular obliteration of the arteriovenous fistula under local anesthesia. Pseudoaneurysm formation or dAVF formation after revascularization surgery is an exceptional case. If patients have such complications, practioner should carefully screen the patients by implementing digital subtraction angiogram to identify anatomic features; as well as consider immediate treatment in any way, including embolization or other surgery

• Journal of Cerebrovascular and Endovascular Neurosurgery
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• v.25 no.4
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• pp.468-472
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• 2023

Bilateral posterior communicating (pComm) artery aneurysms represent only 2% of mirror intracranial aneurysms. Usually, these are surgically approached through bilateral craniotomies for clipping. We present the case of a 50-year-old female presenting with headache and horizontal diplopia. Neurological examination revealed a left oculomotor palsy, with no other neurological deficits. Imaging studies revealed bilateral aneurysmatic lesions in both internal carotid arteries (ICA). A conventional left pterional approach was planned in order to treat the symptomatic aneurysm, and, if deemed feasible, a contralateral clipping through the same approach. The procedure was performed in a hybrid operating room (HOR), performing an intraoperative digital subtraction angiography (DSA) and roadmapping assistance during dissection and clipping. Transoperatively, a post-fixed optic chiasm was identified, with a wide interoptic space, which allowed us to perform the contralateral clipping through a unilateral approach. This technique for clipping bilateral pComm aneurysms can be performed when the proper anatomical features are met.

• Journal of Cerebrovascular and Endovascular Neurosurgery
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• v.25 no.4
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• pp.475-484
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• 2023

Objective: This study aimed to develop microsurgical strategies based on the anatomical relationship between dorsal internal carotid artery (ICA) aneurysms, the falciform ligament (FL), and the anterior clinoid process (ACP). Methods: Between 2017 and 2022, 25 patients with unruptured dorsal ICA aneurysms (less than 4 mm in diameter) underwent microsurgical direct clipping. These cases involved the left ICA (n=17) and the right ICA (n=8), with a mean aneurysm size of 3.3 mm (range, 2.5 to 4 mm). We used computed tomography angiography (CTA) and digital subtraction angiography to elucidate the anatomical relationship between dorsal ICA aneurysms and other structures. All procedures involved an ipsilateral pterional approach with securement of the ipsilateral cervical ICA for proximal control. Results: Among the 25 dorsal ICA aneurysms, 8 (32%) were clipped without the FL being incised. Another 5 (20%) were clipped solely after the FL was cut. For the remaining 12 cases, the aneurysms were successfully clipped following FL incision and partial ACP removal. Patients exhibited favorable postoperative recoveries with good outcomes, and postoperative CTA revealed complete aneurysm clipping without any residual remnants. Conclusions: We were able to perform clipping without removing the ACP in 13 patients (52%), and in 8 of these (32%), the clipping was carried out directly without cutting the FL. Microsurgery, coupled with proximal control of the cervical ICA, can serve as a viable alternative for patients with small dorsal ICA aneurysms, especially when endovascular treatment options are limited, and 3D CTA confirms a clear anatomical relationship with the ACP.