• Proceedings of the KOSOMBE Conference
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• v.1998 no.11
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• pp.279-280
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• 1998

A new algorithm is developed that can reduce the metal artifact on CT caused by pedicle screws. Metal artifact has been recognized as a major problem in precise reading of CT images. In particular, spine surgeons have been bothered with the artifact appearing on CT taken after pedicle screw insertion. To reduce the artifact, our new algorithm first finds the center line from CT images, and then overlays an exact size screw image on the CT. The exact screw is obtained from an actual design specifications of screw, and the CT images are processed to maximize bone margins while minimizing screw images through adjusting the window width and level. 실험 결과 단순한 Window W/L 조절로는 해결되지 않는군요. This algorithm provides spine surgeons with more accurate CT images and thus better interpretation of CT to ascertain the success or failure of pedicle screw insertion.

• The Journal of Korean Society for Radiation Therapy
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• v.13 no.1
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• pp.109-112
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• 2001

1. 목적 : head and neck cancer 환자의, C-T 영상을 이용한 방사선치료계획시 치과 보철물에 의해 발생하는 artifact가 선량 계산에 미치는 영향을 분석하고자 한다. 2. 재료 및 방법:두 경부와 유사한 크기의 Polystyrenes Phantom ($20{\times}20{\times}25cm^3$) 을 제작하고, 팬톰내에 금으로 인공보철물을 제작하여 보철물 부착 전.후를 C-T Scan (High Speed Advantage, GE, US) 하였다. artifact에 의한 영향을 쉽게 분석하기위해 팬톰내에 다른 구조물은 만들지 않았으며 두가지 방법으로 얻어진 영상을 이용하여 조사면의 크기와 조사 방향을 변화 시켜 가며 1문 조사(SSD 100 cm)에 의한 치료 계획(3D RTP system, Prowess, US)을 수립하여 기준점(5,10 cm depth)에서의 선량 변화를 비교 분석하였다. 아울러 3회 반복 scan하여 artifact에 발생 유형과 CTNo을 이용한 density을 분석하였다. 3. 결과: C-T Scan으로 얻어진 image 상에 나타난 Artifact는 CT no $-1000{\sim}+2775$(기준 $-1000{\sim}+3700$)까지의 다양한 값을 가지며 보철물을 기준으로 방사형태로 분포하였다. artifact가 선량 계산에 미치는 영향을 분석한 결과 보철물 사용시 5cm깊이의 기준점에서 절대선량은 평균 $+1.5{\pm}2.8\%$, 10 cm 깊이에서는 $+1.8{\pm}3.5\%$의 오차를 보였다. 조사방향에 의한 오차는 artifact에 대해 측면 조사한(gantry $270^{\circ}$)경우에서 높게 관찰되었다. 4. 결론: 두 경부 종양의 방사선 치료시 치과 보철물에 의한 artifact는 흔히 관찰가능하며 본 실험을 통해 다양한 형태와 다양한 density을 가짐을 알수있었다. 영상에 나타난 정도에 비해 선량계산에 미치는 평균 오차는 낮게 평가되었지만 조사 방향과 보철물의 위치에 따라 변동이 크게 나타날 수 있어 치료 계획시 가능한 artifact의 영향을 적게 받는 빔의 선택이 정확한 선량 계산에 도움을 줄 것으로 사료된다.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.6
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• pp.462-467
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• 2002

A new approach for reducing the blocking artifact is proposed in this paper. This method can be applied to conventional transform coding, without introducing additional information or significant blurring. Main drawbacks of the Discrete Cosine Transform(DCT) are visible block boundaries due to coarse quantization of the coefficients. Therefore, restoration techniques result in unnecessary blurring of the image. The proposed deblocking algorithm is based on the heuristic approach for edge detection. All edges of the standard still images are categorized, and the best edges are selected. Several images are used fer experiments, and several other previous algorithms are compared with the proposed approach. The results show that the proposed algorithm works better than those of other previous researches. This algorithm can be used for JPEG, MPEG, and H.261 standard images.

• The Journal of Korean Society for Radiation Therapy
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• v.17 no.1
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• pp.45-55
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• 2005

Purpose : To evaluate the usefulness of the handmade patient immobilization device and to report the clinical results of it. Materials and methods : We made two fusion images and analyzed those images. One image is made with diagnostic MR image and CT image, the other with therapeutic planning MR image and CT image. With open head holder, we measured the skin dose and attenuation dose. Also, we made the planning CT couch plate with acrylic plate and styrofoam and compared artifact. Results : We could get more accurate fusion image when we use MR head holder(within 2mm error). The skin dose was reduced 2 times and the attenuation dose was reduced more than $20\%$ when open head holder used. The planning CT couch plate was more convenient than conventional board and reduced artifact remarkably. Conclusion : We could verify the localization point in the MR image which is taken with MR head holder. So we could fuse the image more accurately. The same method could be applied to PET and US image, if the alike immobilization device used. With open head holder, the skin dose and the attenuation dose was reduced. And those above devices could substitute for expensive foreign device, if those are manufactured adequately.

• Korean Journal of Radiology
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• v.22 no.8
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• pp.1341-1351
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• 2021

Objective: To compare the quality of various polychromatic and monochromatic images with or without using an iterative metal artifact reduction algorithm (iMAR) obtained from a dual-energy computed tomography (CT) to evaluate total knee arthroplasty. Materials and Methods: We included 58 patients (28 male and 30 female; mean age [range], 71.4 [61-83] years) who underwent 74 knee examinations after total knee arthroplasty using dual-energy CT. CT image sets consisted of polychromatic image sets that linearly blended 80 kVp and tin-filtered 140 kVp using weighting factors of 0.4, 0, and -0.3, and monochromatic images at 130, 150, 170, and 190 keV. These image sets were obtained with and without applying iMAR, creating a total of 14 image sets. Two readers qualitatively ranked the image quality (1 [lowest quality] through 14 [highest quality]). Volumes of high- and low-density artifacts and contrast-to-noise ratios (CNRs) between the bone and fat tissue were quantitatively measured in a subset of 25 knees unaffected by metal artifacts. Results: iMAR-applied, polychromatic images using weighting factors of -0.3 and 0.0 (P_-0.3i and P_0.0i, respectively) showed the highest image-quality rank scores (median of 14 for both by one reader and 13 and 14, respectively, by the other reader; p < 0.001). All iMAR-applied image series showed higher rank scores than the iMAR-unapplied ones. The smallest volumes of low-density artifacts were found in P_-0.3i, P_0.0i, and iMAR-applied monochromatic images at 130 keV. The smallest volumes of high-density artifacts were noted in P_-0.3i. The CNRs were best in polychromatic images using a weighting factor of 0.4 with or without iMAR application, followed by polychromatic images using a weighting factor of 0.0 with or without iMAR application. Conclusion: Polychromatic images combined with iMAR application, P_-0.3i and P_0.0i, provided better image qualities and substantial metal artifact reduction compared with other image sets.

• The Korean Journal of Nuclear Medicine Technology
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• v.18 no.1
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• pp.62-68
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• 2014

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.

• The Korean Journal of Nuclear Medicine Technology
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• v.22 no.1
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• pp.55-66
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• 2018

Purpose In PET/CT exam, washed-out artifact could occur due to severe motion of the patient and high specific activity, it results in lowering not only qualitative reading but also quantitative analysis. Scatter limitation correction by GE is an algorism to correct washed-out artifact and recover the images in PET scan. The purpose of this study is to measure the threshold of specific activity which can recovers to original uptake values on the image shown with washed-out artifact from phantom experiment and to compare the quantitative analysis of the clinical patient's data before and after correction. Materials and Methods PET and CT images were acquired in having no misalignment(D0) and in 1, 2, 3, 4 cm distance of misalignment(D1, D2, D3, D4) respectively, with 20 steps of each specific activity from 20 to 20,000 kBq/ml on $^{68}Ge$ cylinder phantom. Also, we measured the distance of misalignment of foley catheter line between CT and PET images, the specific activity which makes washed-out artifact, $SUV_{mean}$ of muscle in artifact slice and $SUV_{max}$ of lesion in artifact slice and $SUV_{max}$ of the other lesion out of artifact slice before and after correction respectively from 34 patients who underwent $^{18}F-FDG$ Fusion Whole Body PET/CT exam. SPSS 21 was used to analyze the difference in the SUV between before and after scatter limitation correction by paired t-test. Results In phantom experiment, $SUV_{mean}$ of $^{68}Ge$ cylinder decreased as specific activity of $^{18}F$ increased. $SUV_{mean}$ more and more decreased as the distance of misalignment between CT and PET more increased. On the other hand, the effect of correction increased as the distance more increased. From phantom experiments, there was no washed-out artifact below 50 kBq/ml and $SUV_{mean}$ was same from origin. On D0 and D1, $SUV_{mean}$ recovered to origin(0.95) below 120 kBq/ml when applying scatter limitation correction. On D2 and D3, $SUV_{mean}$ recovered to origin below 100 kBq/ml. On D4, $SUV_{mean}$ recovered to origin below 80 kBq/ml. From 34 clinical patient's data, the average distance of misalignment was 2.02 cm and the average specific activity which makes washed-out artifact was 490.15 kBq/ml. The average $SUV_{mean}$ of muscles and the average $SUV_{max}$ of lesions in artifact slice before and after the correction show a significant difference according to a paired t-test respectively(t=-13.805, p=0.000)(t=-2.851, p=0.012), but the average $SUV_{max}$ of lesions out of artifact slice show a no significant difference (t=-1.173, p=0.250). Conclusion Scatter limitation correction algorism by GE PET/CT scanner helps to correct washed-out artifact from motion of a patient or high specific activity and to recover the PET images. When we read the image occurred with washed-out artifact by measuring the distance of misalignment between CT and PET image, specific activity after applying scatter limitation algorism, we can analyze the images more accurately without repeating scan.

• Journal of the Korean Society of Radiology
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• v.7 no.4
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• pp.307-311
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• 2013

This study examined the change of artifact volume by analyzing the level of image change associated with the setting of threshold through 3D imaging in scan parameter(slice thickness and helical pitch) and 3D image reconstruction to explore whether the presence of pathology was fully distinguished when CT was taken by lower dose than the existent dose to reduce exposure. Furthermore, this study attempted to investigate Scan Parameter acceptable in CT to reduce exposure dose. For materials and methods, silicon was used to produce samples. Five spherical samples were produced at 10-millimeter intervals(50, 40, 30, 20, and 10 mm) in diameter and were fixed at 120 Kvp of tube voltage and 50 mA of tube current. Varied slab thickness((1.0, 2.0, 3.0, 5.0, and 7.0mm) and Helical Pitch(1.5, 2.0, 3.0) were scanned. The image at an interval of 1.0, 2.0, 3.0, 5.0, and 7.0mm was transmitted to the workstation. Threshold(-200, -50, 50 ~ 1,000) was changed using the volume rendering technique, 3D image was reconstructed, and artifact volume was measured. In conclusion, 1.5 of Helical Pitch showed the least change of volume and 3.0 of helical pitch showed the greatest reduction of volume change. The experiment suggested that as slice thickness was increased, artifact volume was decreased more than actual measurement. Furthermore, in the 3D image reconstruction, when the range of threshold was set as -200 ~1,000, artifact volume was changed the least. Based on the results, it is expected to have an effect of reducing exposure dose.

• The Journal of the Korea Contents Association
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• v.10 no.9
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• pp.302-308
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• 2010

In MRI, the Ferromagnetic artifact is generated by the metalization within in which the before inspection removal is impossible and the distortion of an image is brought. The distortion measure according to the steel for each sequence of T1 image and magnetic field intensity are analyzed and minimized method is looked into. We used SIEMENS 1.5T and 3.0T MRI for experiment equipment. First, it places within the Phantom making a metalization(Ti+Al, Stainless, Nitinol) on 1.5T, 3.0T MRI and the T1 weighted image for each Sequence is acquired. The distortion of an image and about adjacent portion change of the metal material were compared through the obtained image, we analyzed. In all metalizations, a distortion was generated and a distortion was few in particularly, and Titanium-Aluminium alloy. And the extent of a distortion was worse image in the Turbo spin Echo. The use of the Titanium-Aluminium alloy the inserted in an internal material of the metalization is recommend. and, equipment of 1.5T the patient inserting a metal in an internal is used in an inspection than equipment of 3.0T. Also, the sequence is suitable when it obtains the optimum T1 weighted image of an impersonate to use the Turbo spin Echo.

• Journal of the Korea Society of Computer and Information
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• v.22 no.12
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• pp.69-77
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• 2017

This paper represents a novel framework for multi-scale image fusion. Multi-scale Kalman Smoothing (MKS) algorithm with quad-tree structure can provide a powerful multi-resolution image fusion scheme by employing Markov property. In general, such approach provides outstanding image fusion performance in terms of accuracy and efficiency, however, quad-tree based method is often limited to be applied in certain applications due to its stair-like covariance structure, resulting in unrealistic blocky artifacts at the fusion result where finest scale data are void or missed. To mitigate this structural artifact, in this paper, a new scheme of multi-scale fusion framework is proposed. By employing Super Resolution (SR) technique on MKS algorithm, fine resolved measurement is generated and blended through the tree structure such that missed detail information at data missing region in fine scale image is properly inferred and the blocky artifact can be successfully suppressed at fusion result. Simulation results show that the proposed method provides significantly improved fusion results in the senses of both Root Mean Square Error (RMSE) performance and visual improvement over conventional MKS algorithm.