I-131 SPECT/CT에서 Ringing Artifact 감소를 위한 다양한 Filter값의 적용

김하균,김수미,우재룡,오소원,이재성,김유경,Kim, Ha Gyun,Kim, Soo Mee,Woo, Jae Ryong,Oh, So Won,Lee, Jae Sung,Kim, Yu Kyeong 대한핵의학기술학회 2014 핵의학 기술 Vol.18 No.1

치료 후 I-131 SPECT/CT는 잔류 갑상선 위치확인 및 전이유무를 판단하기 위하여 시행된다. 잔류 갑상선에 집적이 심한 경우 영상은 ringing artifact에 의하여 왜곡된다. 본 연구는 ringing artifact를 제거하고 영상의 질을 향상시키기 위한 적절한 post-filter의 적용에 대하여 제시하고자 한다. 본 실험은 hollow sphere와 아크릴통으로 구성된 phantom을 사용하여 SPECT/CT Discovery 670 (GE Healthcare, USA) 장비로 수행하였다. I-131용액을 hollow sphere에 184, 46, 9.2, 2.3 MBq/cc, 아크릴통에 46 kBq/cc을 각각 주입하였고 sphere 대 background의 비를 4000:1, 1000:1, 200:1, 50:1로 설정하였다. 데이터는 다음과 같은 조건으로 획득하였다(HEGP collimator 사용, Attenuation collection 적용, scan time 40 secs/frame, step angle 6도, scan mode non circular, evolution 적용과 미적용). 획득된 데이터는 OSEM (iteration 2, subset 10) 방식으로 재구성하였다. Post-filer의 사용에 따른 이미지의 변화를 보기 위해 3가지의 다른 post-filer들이 사용되었다(butterworth filter cut-off: 0.38, 0.43, 0.48, 0.53, 0.58, hanning filter cut-off: 0.8, 0.85, 0.9, 0.95, 1, gaussian FWHM: 3, 3.4, 4, 4.5, 5). 각각의 데이터는 MRIcro를 사용하여 contrast ratio, background variability를 분석하였고 e.soft ROI tool을 사용하여 FWHM값을 구하였다. Evolution을 적용한 경우, 모든 결과에서 contrast ratio값이 높게 나타났다. Evolution을 적용하지 않은 경우 star artifact 등 왜곡이 발생하였고 영상의 질이 현저히 낮아짐을 확인할 수 있었다. 4000:1, 1000:1, 200:1의 경우, butterworth filter 사용 시 ringing artifact가 발생하였으며 cut-off값이 커질수록 artifact가 감소하였다. Hanning filter를 사용한 경우 ringing artifact는 발생하지 않았다. Contrast ratio와 FWHM값이 butterworth filter나 hanning filter 적용 시 우수하였다. Gaussian filter경우 contrast ratio와 FWHM값에서 저조한 결과를 얻을 수 있었다. 50:1의 경우, 모든 경우에서 ringing artifact가 발생하지 않았다. Butterworth filter를 적용한 경우 가장 높은 contrast ratio와 가장 우수한 FWHM값을 나타내었다. 본 논문을 통하여 I-131 SPECT에서 ringing artifact가 발생 할 경우(thyroid remnant를 포함) hanning filter를 사용하여 영상을 재구성하고, ringing artifact가 발생하지 않을(remnant thyroid를 포함하지 않음) 경우 butterworth filter를 사용하여 재구성하는 것이 바람직하다는 사실을 알 수 있었다. Purpose: After I-131 therapy, SPECT/CT is useful in identifying location of thyroid remnants and metastasis of thyroid cancers. An excessive uptake of thyroid leads to a ringing artifact in the SPECT images. The aim of this study is to investigate and suggest a proper post filters to remove ringing artifact and produce better image quality. Materials and Methods: A low-cost, customized thyroid-mimicking phantom, consisting of an acrylic bottle and a hollow sphere was used for SPECT/CT Discovery (GE Healthcare, USA). It was filled with I-131 solution. The ratio of hollow sphere to background were varied as 50:1, 200:1, 1000:1 and 4000:1. Acquired images were reconstructed by OSEM (2 iterations, 10 subsets) with and without Evolution (resolution recovery correction, GE). Three different post-filters were applied; Butterworth (cut off: 0.38 to 0.58 with intervals of 0.05), Hanning (cut off: 0.8 to 1 with intervals of 0.05) and Gaussian (FWHM: 3 to 5 with intervals of 0.5) filters. Contrast, background variability, air area variability, and full width half maximum (FWHM) were compared. Results: Higher contrasts were obtained from the SPECT images with Evolution than without Evolution. In the case of images without Evolution, image distortion such as star artifact was generated. For all sphere-to-background ratio, the Butterworth filter showed better constrasts and FWHMs than other two filters, but the ringing artifact was still generated in all studies except 50:1 and it was decreased as cutoff value was increased. The ringing artifact didn't appear with Hanning and Gaussian filters at all studies, however constrats and FWHMs with Gaussian was worse than Hanning filter. For the images having ringing artifacts, the background variability and air area variability were increased. Conclusion: In this study, we suggested that it is desirable to use Hanning filter when the ringing artifact is generated and to use Butterworth filter when ringing artifact is not generated in I-131 SPECT.

웨이블릿 변환을 이용한 영상복원의 물결현상 제거 방법

윤진영(Jinyoung Youn),유윤종(Yoonjong Yoo),전신영(Sinyoung Jun),신정호(Jeongho Shin),백준기(Joonki Paik) 대한전자공학회 2008 電子工學會論文誌-SP (Signal processing) Vol.45 No.6

디지털 영상이 멀티미디어의 핵심 매체로 자리를 잡게 되면서 영상의 열화요인을 제거하여 원래의 품질에 가깝게 개선하는 영상복원기술의 활용분야가 더욱 늘어나고 있다. 그러나 영상복원을 수행할 때 영상의 열화(degradation)가 선형공간불변이라고 가정하기 때문에 주파수영역에서 영상복원을 수행하면 그 결과 에지와 같이 밝기값의 변화가 큰 영역 주변에서 물결현상(ringing)이 나타나는 단점이 있다. 본 논문은 물결현상 제거를 위해 새로운 적응적 후처리 필터링 방법을 제안한다. 제안하는 알고리즘은 웨이블릿 변환을 사용하여 영상을 해석하고 에지맵을 추출하고 영역을 나누어 에지영역과 물결현상을 검출한 후 이를 쌍방향필터(bilateral filter)를 이용해 제거한다. 실험결과를 통해서 제안하는 방법이 효과적으로 물결현상을 제거하는 동시에 중요한 에지를 보존할 수 있음을 확인할 수 있다. Digital image find own level core media in multimedia as image restoration technology fields, which remove degradation factor for image enhancement, have been growing. Linear space-invariant image restoration algorithms often introduce ringing artifacts near sharp intensity transition areas. This paper presents a new adaptive post-filtering algorithm for reducing ringing artifact. The proposed method extracts an edge map of the image using wavelet transform. Based on the edge information, ringing artifacts are detected, and removed by an adaptive bilateral filter. Experimental results show that the proposed algorithm can efficiently remove ringing artifacts with edge preservation.

Fast blocking and ringing artifacts removal in JPEG-coded images

( Ekaterina V. Tolstaya ),( Michael N. Rychagov ),( Sang Ho Kim ),( Don Chul Choi ) 한국화상학회 2010 한국화상학회지 Vol.16 No.3

The paper relates to a method for effective reduction of artifacts, caused by JPEG coding. Most common artifacts produced by such type of coding, are blocking and ringing artifacts. To reduce the effect of coding artifacts, a variety of different algorithms and methods has been suggested. However, the majority of solutions propose to process all blocks in the image, which leads to increase of processing time, required resources, as well as image over-blurring after processing of blocks. In this paper we describe very effective procedures for detection of artifacts, and their subsequent correction. This approach helps to save notable amount of computational resources, since not all the blocks are involved in correction procedures. Detection steps are performed in frequency domain, using only DCT coefficients of an image. Numerous examples have been analyzed and compared with the existent solutions, and results prove the effectiveness of proposed technique.

평판 디텍터 기반 마이크로 CT시스템을 위한 Ring Artifact 보정 방법

김규원,이수열,조민형,Kim, Gyu-Won,Lee, Soo-Yeol,Cho, Min-Hyoung 대한의용생체공학회 2009 의공학회지 Vol.30 No.6

The most troublesome artifacts in micro computed tomography (micro-CT) are ring artifacts. The ring artifacts are caused by non-uniform sensitivity and defective pixels of the x-ray detector. These ring artifacts seriously degrade the quality of CT images. In flat-panel detector based micro-CT systems, the ring artifacts are hardly removed by conventional correction methods of digital radiography, because very small difference of detector pixel signals may make severe ring artifacts. This paper presents a novel method to remove ring artifacts in flat-panel detector based micro-CT systems. First, the bad lines of a sinogram which are caused by defective pixels of the detector are identified, and then, they are corrected using a cubic spline interpolation technique. Finally, a ring artifacts free image is reconstructed from the corrected projections. We applied the method to various kinds of objects and found that the image qualities were much improved.

Blind Post-Processing for Ringing and Mosquito Artifact Reduction in Coded Videos

Seok Bong Yoo,Kyuha Choi,Jong Beom Ra IEEE 2014 IEEE Transactions on Circuits and Systems for Vide Vol.24 No.5

<P>Block-based video-coding standards produce unwanted spatial and temporal artifacts in reconstructed videos. Among them, ringing and mosquito artifacts arise due to the quantization of high-frequency discrete cosine transform coefficients. Most of the existing artifact-reduction algorithms assume that coding information such as a standard quantization table and the corresponding quantization parameter for each block are available. In many multimedia applications, however, external video inputs are usually supplied without coding information. To effectively reduce the ringing and mosquito artifacts in a decoded input video sequence, it is necessary to control the filter strength block by block. In this paper, we present a blind block-based method to estimate the quantization amount and propose a novel post-processing algorithm based on the visibility of artifacts in terms of the human visual system using the estimated quantization amount. Experimental results demonstrate that the proposed algorithm better alleviates ringing and mosquito artifacts in various coded videos compared with the existing algorithms.</P>

Minimizing Ringing Artifact of Image Restoration Using Autocorrelation

Jinyoung Kang,Donggyun Kim,Joonki Paik 중앙대학교 영상콘텐츠융합연구소 2015 TechArt :Journal of Arts and Imaging Science Vol.2 No.3

Linear space-invariant image-restoration algorithms often introduce ringing artifacts near sharp intensity transition areas. This paper presents a new adaptive post-filtering algorithm to reduce the ringing artifacts. The proposed method extracts an edge map of the image using autocorrelation. On the basis of the edge information, ringing artifacts are detected and removed by an adaptive bilateral filter. Experimental results show that the proposed algorithm can efficiently remove ringing artifacts with edge preservation.

고려시대 魚子文 금속공예품 연구

임지윤 한국미술사학회 2011 美術史學硏究 Vol.271272 No.271272

魚子文기법은 금속표면에 끝부분이 둥글게 움푹 파인 釘을 망치로 두드려 작은 음각 圓文을 표현하는금속공예기법이다. 이 기법은 기원전부터 고대 서아시아 등에서 보이기 시작하여 중국을 거쳐 한국으로 전래되었다. 어자문기법은 7세기 이전까지 금속기의 부분 장식으로 이용되다가 唐代 金銀器에서 주문양을 돋보이게 하는 바탕 장식[地文]으로 성행하였다. ‘魚子’는 작은 원문을 수없이 늘어놓은 모습이 물고기 알처럼보인다 하여 붙여진 명칭으로, 일본 正倉院文書의 기록(760)에 근거하여 현재 보편적으로 불리고 있다. 어자문기법은 삼국시대에 문양의 일부, 또는 테두리를 장식하는 연주문 형태로 고급 威勢品과 金銅小形佛 등에 나타나기 시작하였다. 바탕 장식으로 사용된 시기는 唐과 활발한 교섭을 하였던 7세기 전반 경으로, 왕실사찰에서 출토된 舍利器에서 정착되어 가는 초기단계를 볼 수 있다. 통일신라시대에 어자문은 경주를 중심으로 제작된 불교공예품과 일부 장식품에 본격적으로 시문되었다. 고려시대에 어자문기법은 삼국·통일신라 공예기술의 전통을 기반으로 北宋·遼 등과의 대외교섭을 통해 11세기에서 12세기에 전성기를 이루었다. 특히 11세기에 요와의 밀접한 관계는 어자문 금속공예품의 제작에 상당한 영향을 끼쳤을 것으로 판단된다. 이와 더불어 고려전기에 官匠의 제도화를 토대로 한 官營手工業의 체계적인 생산체제는 어자문 금속공예품의 발전에 큰 원동력이 되었을 것이다. 고려시대 어자문 금속공예품은 왕실과 귀족층 등으로 수요가 확산되면서 기명류·화장용구·장신구 등의 일상공예품에 폭넓게 제작되었다. 어자문기법은 대표적인 주문양 기법인 線彫기법과 打出기법 등과의 결합에 따라서 시문수법에 영향을 받는다. 선조기법과 함께 장식된 어자문기법은 선조기법과 대등하게 음각된 원문 하나하나가 육안으로 분명하게 확인된다. 어자문기법의 유형은 성기거나 불규칙적인 유형과 치밀하고 정연한 유형으로 나눌 수있다. 전자는 통일신라 말의 경향을 이어 제작된 고려 초의 불교공예품에서 자주 보이며, 후자는 화장용구와 장신구 등이 해당된다. 高浮彫 타출기법과 결합된 어자문기법은 빽빽하게 타출한 꽃문양의 사이마다 눈에 보이지 않을 정도로 깨알 같이 시문되었다. 어자문은 凹凸의 차이에 따른 빛의 반사와 광택효과로 금속질감에 변화를 주어, 화려함을 더하고 주문양의 입체감을 더욱 강조하였다. 이처럼 금속공예품의 全面을 가득채운 고부조 타출기법과 질서정연하고 빈틈없는 어자문기법의 조합은, 요대 금은기에서도 볼 수 없는 고려만의 독자적인 특징으로서 늦어도 12세기를 下限으로 성행하였다고 생각된다. 본 논문은 고려시대 어자문기법 연구의 始發點으로서, 한국에 전래된 어자문기법의 전개과정과 그동안 주목받지 못했던 고려시대 어자문 금속공예품의 우수성과 독자성을 살펴보는 데 의의가 있다. The ring-matting technique is a metalworking technique consisting in hammering a burin with a hollow round head onto the surface of a metal item to create small ring-matted patterns in intaglio. This technique was used since before the beginning of the Common Era, and was brought from ancient West Asia to China, then to the Korean peninsula. Ringmatting was used until the early 7th century, only in small areas of a metal item. Since then,the technique had come to be popularly used in Tang China, to create background patterns in gold and silver items. The‘Eoja(魚子)’means literally‘fish roe’for ring-matted patterns, as the small round circles densely gathered together are reminiscent indeed of fish roes. This name, appearing in a record held in Japan’s Shosoin (760), is currently in use also in China and Japan. Ring-matted patterns first appeared in the Korean peninsula, during the Three Kingdoms period, in small areas of an item or as a bead band at the edges of an item. Initially, they were mostly seen on prestige items and small gilt-bronze Buddhist sculptures. The ring- matting technique was later used to create background patterns from the early 7th century when there was active artistic interaction between the Three Kingdoms and Tang China. Early examples of ring-matted background patterns are seen in sarira reliquary items, discovered in Buddhist temples protected by the royal house. During the UnifiedSilla period, the ring-matting was popularly used for decorating Buddhist craft items and some other ornamental items. Meanwhile, we know from the Shosoin record of ring-matting artisans during Nara-period who specialized in ring-matting active but also seemed to be highly considered in the Unified Silla. The Three Kingdoms-period and Unified Silla technique of ring-matting was transmitted to the ensuing period of the Goryeo, and reached its heyday in the 11th to 12th century, helped by the exchange with the Northern Song and Liao. The close ties formed with the state of Liao in the 11th century appear to have had a particularly important influence on the production of ring-matted metal craft items in the Goryeo. Meanwhile,the government artisan system, put into place in the early Goryeo, enabled a more systemic production of craft items; another major contributing factor to the thriving of ring-matted metal crafts. As the demand for ring-matted metal items grew in the royal house and among aristocrats, this metalworking technique was now applied to everyday items like vessels,grooming tools, and accessories. The ring-matting technique was later coupled with other major metalworking techniques such as chasing and repousse. When the ring-matting technique is used together with chasing, each of the ring patterns in intaglio is clearly cut, as distinct as the grooves created through chasing. There are two types of ring-matted patterns: sparse and irregular patterns and densely-gathered and regularly-shaped patterns. Patterns of the former type are mainly seen in late Unified-Silla metal items and also quite frequently employed in early-Goryeo Buddhist craft items. Patterns of the latter type, meanwhile, are often seen in grooming tools and accessories. Ring-matted patterns, when coupled with high-relief repousse patterns, look like tiny granules, densely filling the spaces between repousse floral patterns. Concave and convex ring-matted patterns reflect light in different manners. The lustrous effect produced by ring-matting helps create variation in the texture of a metal item,while adding brilliance to the overall surface design and depth to main motifs. Metal items with high-relief repousse patterns and even ring-matted patterns covering the background completely were only produced in the Goryeo period and uniquely characterize Goryeo metalwork. Such combination was not seen, for instance, in gold and silver items of the Liao state. The popularity of the combination of ring-matting and repousse methods appea...

X-ray micro-CT 이미지 내 패임 및 동심원상 화상결함 제거를 위한 이미지 보정 기법

정연종,김광염,윤태섭,주진현 한국지반공학회 2011 한국지반공학회논문집 Vol.27 No.11

High quality X-ray computed microtomography (micro-CT) imaging of internal microstructures and pore space in geomaterials is often hampered by some inherent noises embedded in the images. In this paper, we introduce image calibration techniques for removing the most common noises in X-ray micro-CT, cupping (brightness difference between the periphery and central regions) and ring artifacts (consecutive concentric circles emanating from the origin). The artifacts removal sequentially applies coordinate transformation, normalization, and low-pass filtering in 2D Fourier spectrum to raw CT-images. The applicability and performance of the techniques are showcased by describing extraction of 3D pore structures from micro-CT images of porous basalt using artifacts reductions, binarization, and volume stacking. Comparisions between calibrated and raw images indicate that the artifacts removal allows us to avoid the overestimation of porosity of imaged materials, and proper calibration of the artifacts plays a crucial role in using X-ray CT for geomaterials.

Investigation of Ring Artifact Using Algebraic Reconstruction Technique

Kwon Su Chon 한국방사선학회 2018 한국방사선학회 논문지 Vol.12 No.1

CT 장치는 물체 내부의 단면 영상 획득이 가능하기 때문에 여러 분야에 광범위하게 사용되고 있다. 단면 영상을 획득하는 여러 단계의 에러 요인들로 인해 다양한 아티팩트가 유발되고 있다. 장치에 의해 발생하는 링 아티팩트를 조사하였다. 512 × 512 크기의 수치 팬텀을 구현하고 대수적 재구성 기법으로 링 아티팩트의 특성을 연구하였다. 프로그램은 Visual C++로 작성하였으며 720개의 투영 및 1,280개의 검출기 픽셀을 갖는 상황에서 구현하였다. 링 아티팩트는 검출기 픽셀의 검출 효율이 서로 달라서 발생한다는 것을 확인하였다. Ring Value 값이 증가할수록 Ring Intensity의 값도 증가하였고, 영상의 원점에 가까울수록 링 아티팩트가 강하게 나타났다. 단면 영상에서 링 아티팩트가 발생하는 위치를 파악하고 역으로 검출기 픽셀의 위치를 추적해 검출효율을 보정함으로써 링 아티팩트를 제거할 수 있을 것이다. Computed tomography system is widely used on various fields because section image of an object can be acquired. During several step to obtain section image, artifacts by many error factors can be added on the image. Ring artifact induced by the CT system is examined in this study. A test phantom of 512 × 512 size was constructed numerically, and the ring artifact was investigated by the algebraic reconstruction technique. The computer program was realized using Visual C++ under the fan beam geometry with projections of 720 and detector pixel of 1,280. The generation of ring artifact was verified by applying different detection efficiency on detector pixels. The ring intensity became large as increasing the ring value, and the ring artifacts were strongly emphasized near the center of the reconstructed image. The ring artifact may be eliminated by tracking the position of ring artifact on the reconstructed image and by calibrating the detector pixel.

대수적 재구성 기법을 통한 링 아티팩트 조사

천권수(Kwon Su Chon) 한국방사선학회 2018 한국방사선학회 논문지 Vol.12 No.1

CT 장치는 물체 내부의 단면 영상 획득이 가능하기 때문에 여러 분야에 광범위하게 사용되고 있다. 단면 영상을 획득하는 여러 단계의 에러 요인들로 인해 다양한 아티팩트가 유발되고 있다. 장치에 의해 발생하는 링 아티팩트를 조사하였다. 512 × 512 크기의 수치 팬텀을 구현하고 대수적 재구성 기법으로 링 아티팩트의 특성을 연구하였다. 프로그램은 Visual C++로 작성하였으며 720개의 투영 및 1,280개의 검출기 픽셀을 갖는 상황에서 구현하였다. 링 아티팩트는 검출기 픽셀의 검출 효율이 서로 달라서 발생한다는 것을 확인하였다. Ring Value 값이 증가할수록 Ring Intensity의 값도 증가하였고, 영상의 원점에 가까울수록 링 아티팩트가 강하게 나타났다. 단면 영상에서 링 아티팩트가 발생하는 위치를 파악하고 역으로 검출기 픽셀의 위치를 추적해 검출효율을 보정함으로써 링 아티팩트를 제거할 수 있을 것이다. Computed tomography system is widely used on various fields because section image of an object can be acquired. During several step to obtain section image, artifacts by many error factors can be added on the image. Ring artifact induced by the CT system is examined in this study. A test phantom of 512 × 512 size was constructed numerically, and the ring artifact was investigated by the algebraic reconstruction technique. The computer program was realized using Visual C++ under the fan beam geometry with projections of 720 and detector pixel of 1,280. The generation of ring artifact was verified by applying different detection efficiency on detector pixels. The ring intensity became large as increasing the ring value, and the ring artifacts were strongly emphasized near the center of the reconstructed image. The ring artifact may be eliminated by tracking the position of ring artifact on the reconstructed image and by calibrating the detector pixel.