• Imaging Science in Dentistry
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• 제38권1호
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• pp.7-15
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• 2008

Purpose: This study provides comparative measurements of absorbed and effective doses for newly developed cone beam computed tomography (CT) in comparison with these doses for conventional CT. Materials and Methods: Thermoluminescent dosimeter rods (TLD rod: GR-200, Thermo Fisher Scientific Inc., Waltham, MA, USA) were placed at 25 sites throughout the layers of Male ART Head and Neck Phantom (Radiology Support Devices Inc., Long Beach, USA) for dosimetry. Implagraphy, DCT Pro (Vatech Co., Hwasung, Korea) units, SCT-6800TXL (Shimadzu Corp., Kyoto, Japan), and Crane x 3+(Soredex Orion Corp., Helsinki, Finland) were used for radiation exposures. Absorption doses were measured with Harshaw 3500TLD reader (Thermo Fisher Scientific Inc., Waltham, MA, USA). Radiation weighted doses and effective doses were measured and calculated by 2005 ICRP tissue weighting factors. Results: Absorbed doses in Rt. submandibular gland were 110.57 mGy for SCT 6800TXL (Implant), 24.56 mGy for SCT 6800TXL (3D), 22.39 mGy for Implagraphy 3, 7.19 mGy for DCT Pro, 5.96 mGy for Implagraphy 1, 0.70 mGy for Cranex 3+. Effective doses $(E_{2005draft)$ were 2.551 mSv for SCT 6800TXL (Implant), 1.272 mSv for SCT 6800TXL (3D), 0.598 mSv for Implagraphy 3, 0.428 mSv for DCT Pro and 0.146 mSv for Implagraphy 1. These are 108.6, 54.1, 25.5, 18.2 and 6.2 times greater than panoramic examination (Cranex 3+) doses (0.023mSv). Conclusion: Cone beam CT machines recently developed in Korea, showed lower effective doses than conventional CT. Cone beam CT provides a lower dose and cost alternative to conventional CT, promising to revolutionize the practice of oral and maxillofacial radiology.

• 한국컴퓨터그래픽스학회논문지
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• 제7권2호
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• pp.29-35
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• 2001

영상기반 가상현실 시스템에서 사용되는 가상환경은 영상모자익(image mosaics)을 통해 만들어진 파노라마 영상으로 표현할 수 있다. 이 경우 실린더 파노라마 영상은 생성 시 제약성 때문에 고정 시점에 방향만을 바꿀 수 있는 탐색을 지원하다. Shum은 가상환경 내에서 자유로운 시점이동을 제공하기 위해 카메라를 일정한 간격으로 회전시켜 얻은 영상으로부터 동심원을 이루는 여러 개의 실린더 형태인 광필드(light field)의 4차원 함수를 세 개의 파라미터, 즉 중심으로부터 거리, 높이, 각도의 3차원 함수로 단순화시킨 동심원 모자익(concentric mosaics)을 제안하였다[10]. 그러나, 이 방법은 카메라의 동일한 간격의 수평 회전운동에 의해 영상을 얻어야 하기 때문에 특별한 장치가 필요하고, 중심으로부터의 거리에 따라 카메라를 배치시켜 촬영함으로써 많은 영상을 처리해야하는 단점이 있다. 본 논문에서는 Shum의 동심원 모자익 생성시의 단점을 보완하기 위하여 영상 스트립을 실린더 평면에 배치시키는 방법을 이용한 효율적인 동심원 모자익 생성 알고리즘을 제안한다. 이는 영상 촬영 시 자유로운 수평 회전이 가능하여 부가적인 촬영장치가 필요하지 않다. 또한 새로운 시점에 대한 영상을 생성할 때, 보간 영상의 사용을 최소화하여 영상의 질을 향상시켰다.

• Imaging Science in Dentistry
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• 제48권3호
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• pp.201-212
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• 2018

Purpose: The aim of this study was to compare cone-beam computed tomography (CBCT) and digital panoramic radiography (DPR) for the detection of pulp stones. Materials and Methods: DPR and CBCT images of 202 patients were randomly selected from the database of our department. All teeth were evaluated in sagittal, axial, and coronal sections in CBCT images. The systemic condition of patients, the presence of pulp stones, the location of the tooth, the group of teeth, and the presence and depth of caries and restorations were recorded. The presence of pulp stones in molar teeth was compared between DPR and CBCT images. Results: Pulp stones were identified in 105 (52.0%) of the 202 subjects and in 434 (7.7%) of the 5,656 teeth examined. The prevalence of pulp stones was similar between the sexes and across various tooth locations and groups of teeth (P>.05). A positive correlation was observed between age and the number of pulp stones(${\rho}=0.277$, P<.01). Pulp stones were found significantly more often in restored or carious teeth (P<.001). CBCT and DPR showed a significant difference in the detection of pulp stones(P<.001), which were seen more often on DPR than on CBCT. Conclusion: DPR, as a 2D imaging system, has inherent limitations leading to the misinterpretation of pulp stones. Restored and carious teeth should be carefully examined for the presence of pulp stones. CBCT imaging is recommended for a definitive assessment in cases where there is a suspicion of a pulp stone on DPR.

• Imaging Science in Dentistry
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• 제42권3호
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• pp.155-161
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• 2012

Purpose: This study was performed to investigate the prevalence, morphology, and calcification pattern of the elongated styloid process in the Mathura population and its relation to gender, age, and mandibular movements. Materials and Methods: The study analyzed digital panoramic radiographs of 2,706 adults. The elongated styloid process was classified with the radiographic appearance based on the morphology and calcification pattern. The limits of mandibular protrusion were evaluated for each subject. The data were analyzed by using a Student's t-test and chi-squared test with significance set at p=0.05. Results: Bilateral elongation having an "elongated" type styloid process with a "partially mineralized" pattern was the most frequent type of styloid process. No correlation was found between styloid process type and calcification pattern on the one hand and gender on the other, although elongated styloid was more prevalent in older and male populations (p<0.05). Further styloid process elongation showed no effect on mandibular protrusive movement (p>0.05). Conclusion: Dentists should recognize the existence of morphological variation in elongated styloid process or Eagle syndrome apparent on panoramic radiographs. We found higher prevalence of elongated styloid process in the population of the Mathura region when compared with other Indian populations. The calcification of the styloid process was more common in the older age group with no correlation to gender, mandibular movement and site. "Type I" with a "partially calcified" styloid process was observed more frequently in the population studied.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
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• pp.390-392
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• 2003

Video mosaicing techniques have been widely used in virtual reality environments. Especially in GIS field, video mosaics are becoming more and more common in representing urban environments. Such applications mainly use spherical or panoramic mosaics that are based on images taken from a rotating camera around its nodal point. The viewpoint, however, is limited to location within a small area. On the other hand, 2D-mosaics, which are based on images taken from a translating camera, can acquire data in wide area. The 2D-mosaics still have some problems : it can‘t be applied to images taken from a rotational camera in large angle. To compensate those problems , we proposed a novel method for creating video mosaics in 3D space. The proposed algorithm consists of 4 steps: feature -based optical flow detection, camera orientation, 2D-image projection, and image registration in 3D space. All of the processes are fully automatic and successfully implemented and tested with real images.

• 로봇학회논문지
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• 제17권3호
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• pp.353-358
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• 2022

Due to the limited field of view of the pinhole camera, there is a lack of stability and accuracy in camera pose estimation applications such as visual SLAM. Nowadays, multiple-camera setups and large field of cameras are used to solve such issues. However, a multiple-camera system increases the computation complexity of the algorithm. Therefore, in multiple camera-assisted visual simultaneous localization and mapping (vSLAM) the multi-view tracking algorithm is proposed that can be used to balance the budget of the features in tracking and local mapping. The proposed algorithm is based on PanoSLAM architecture with a panoramic camera model. To avoid the scale issue 3D LiDAR is fused with omnidirectional camera setup. The depth is directly estimated from 3D LiDAR and the remaining features are triangulated from pose information. To validate the method, we collected a dataset from the outdoor environment and performed extensive experiments. The accuracy was measured by the absolute trajectory error which shows comparable robustness in various environments.

• 한국전자통신학회논문지
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• 제6권6호
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• pp.831-838
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• 2011

컴퓨터 그래픽스 적용분야에서 표현되는 모습들은 현실 세계의 모습을 기반으로 컴퓨터 비전(Computer Vision) 분야에서는 사실적인 3D(Dimension) 모델 또는 가상 환경을 구축하기 위한 연구가 활발하게 진행되고 있다. 3D 디스플레이의 발전과 보급으로 인해 사용자들이 입체감 있는 3차원 가상현실을 손쉽게 접할 수 있게 됨에 따라 가상현실 콘텐츠에 대한 수요가 증가되고 있다. 본 논문은 소실점 위치에 따른 깊이지도 생성 기법을 이용하여 3D 파노라마 시스템을 제안했다. 3D 파노라마는 사용자에게 마치 촬영 장소에 서서 주위를 살펴보는 것과 같은 입체감 있는 효과가 나타난다. 또한, 3D 파노라마 시스템은 넓은 영역에 대해 근거리의 사물과 원거리의 배경에 대한 자유로운 시점과 변함없는 고화질의 사진과 같은 현실감 있는 3차원 입체영상이 제공된다.

• 한국해양환경ㆍ에너지학회지
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• 제3권1호
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• pp.25-34
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• 2000

이중유벽 사이에 가두어진 기름층과 전방 유벽의 끝에서 발생하는 보오텍스 거동간의 관계를 보기 위하여 파노라마 PIV 기법을 사용하였다. 물-기름 자유경계면 근처의 순간 및 시간평균 경계층 유속분포를 계측하여 경계면 상의 전단응력 도출가능성을 확인하였다. 본 기법을 사용하면 자유경계면의 거동이 작거나 규칙적인 경우 경계면상 전단층내 상세 유동구조를 파악하기 충분한 정도의 해상도를 가진 결과를 얻을 수 있다고 판단되었다.

• Maxillofacial Plastic and Reconstructive Surgery
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• 제37권
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• pp.30.1-30.7
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• 2015

Background: The inferior alveolar nerve (IAN) may be injured during extraction of the mandibular third molar, causing severe postoperative complications. Many methods have been described for evaluating the relative position between the mandibular third molar and the inferior alveolar canal (IAC) on panoramic radiography and computed tomography, but conventional radiography provides limited information on the proximity of these two structures. The present study assessed the benefits of three-dimensional computed tomography (3D-CT) prior to surgical extraction of the mandibular third molar, to prevent IAN damage. Methods: This retrospective study included 4917 extractions in 3555 patients who presented for extraction of the mandibular third molars. The cases were classified into three groups, according to anatomical relationship between the mandibular third molars and the IAC on panoramic radiography and whether 3D-CT was performed. Symptoms of IAN damage were assessed using the touch-recognition test. Data were compared using the chi-square test and Fisher's exact test. Results: Among the 32 cases of IAN damage, 6 cases were included in group I (0.35 %, n = 1735 cases), 23 cases in group II (1.1 %, n = 2063 cases), and 3 cases in group III (0.27 %, n = 1119 cases). The chi-square test showed a significant difference in the incidence of IAN damage between groups I and II. No significant difference was observed between groups I and III using Fisher's exact test. In the 6 cases of IAN damage in group I, the mandibular third molar roots were located lingual relative to the IAC in 3 cases and middle relative to the IAC in 3 cases. The overlap was ${\geq}2mm$ in 3 of 6 cases and 0-2 mm in the remaining 3 cases. The mean distance between the mandibular third molar and IAC was 2.2 mm, the maximum distance 12 mm, and the minimum distance 0.5 mm. Greater than 80 % recovery was observed in 15 of 32 (46.8 %) cases of IAN damage. Conclusions: 3D-CT may be a useful tool for assessing the three-dimensional anatomical relationship and proximity between the mandibular third molar and IAC in order to prevent IAN damage during extraction of mandibular third molars.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 신호처리소사이어티 추계학술대회 논문집
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• pp.187-190
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• 2003

In this paper, we propose an extrinsic calibration method for a multi-view camera to get an optimal pose in 3D space. Conventional calibration algorithms do not guarantee the calibration accuracy at a mid/long distance because pixel errors increase as the distance between camera and pattern goes far. To compensate for the calibration errors, firstly, we apply the Tsai's algorithm to each lens so that we obtain initial extrinsic parameters Then, we estimate extrinsic parameters by using distance vectors obtained from structural cues of a multi-view camera. After we get the estimated extrinsic parameters of each lens, we carry out a non-linear optimization using the relationship between camera coordinate and world coordinate iteratively. The optimal camera parameters can be used in generating 3D panoramic virtual environment and supporting AR applications.