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Je, U.K.,Park, C.K.,Lim, H.W.,Cho, H.S.,Lee, D.Y.,Lee, H.W.,Kim, K.S.,Park, S.Y.,Kim, G.A.,Kang, S.Y.,Park, J.E.,Kim, W.S.,Jeon, D.H.,Woo, T.H. Elsevier BV * North-Holland 2017 Nuclear Instruments & Methods in Physics Research. Vol. No.
<P><B>Abstract</B></P> <P>We have recently developed precise x-ray grids having strip densities in the range of 100 – 250 lines/inch by adopting the precision sawing process and carbon interspace material for the demands of specific x-ray imaging techniques. However, quality assurance in the grid manufacturing has not yet satisfactorily conducted because grid strips of a high strip density are often invisible through an x-ray nondestructive testing with a flat-panel detector of an ordinary pixel resolution (>100 μ m). In this work, we propose a useful method to evaluate actual grid strip densities over the Nyquist sampling rate based on the moiré artifact analysis. We performed a systematic simulation and experiment with several sample grids and a detector having a 143- μ m pixel resolution to verify the proposed quality assurance method. According to our results, the relative differences between the nominal and the evaluated grid strip densities were within 0.2% and 1.8% in the simulation and experiment, respectively, which demonstrates that the proposed method is viable with an ordinary detector having a moderate pixel resolution for quality assurance in grid manufacturing.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The precise carbon-interspaced antiscatter grids have been studied. </LI> <LI> It is proposed for a useful method to evaluate actual grid strip densities over the Nyquist sampling rate based on the moiré artifact analysis. </LI> <LI> The simulation and experimental results demonstrate that the proposed method is viable with an ordinary detector having a moderate pixel resolution (>100 μ m) for quality assurance in grid manufacturing. </LI> </UL> </P>
Je, U.K.,Lee, M.S.,Cho, H.S.,Hong, D.K.,Park, Y.O.,Park, C.K.,Cho, H.M.,Choi, S.I.,Woo, T.H. Elsevier 2015 Nuclear Instruments & Methods in Physics Research. Vol.784 No.-
<P><B>Abstract</B></P> <P>In practical applications of three-dimensional (3D) tomographic imaging, there are often challenges for image reconstruction from insufficient sampling data. In computed tomography (CT), for example, image reconstruction from sparse views and/or limited-angle (<360°) views would enable fast scanning with reduced imaging doses to the patient. In this study, we investigated and implemented a reconstruction algorithm based on the compressed-sensing (CS) theory, which exploits the sparseness of the gradient image with substantially high accuracy, for potential applications to low-dose, high-accurate dental cone-beam CT (CBCT). We performed systematic simulation works to investigate the image characteristics and also performed experimental works by applying the algorithm to a commercially-available dental CBCT system to demonstrate its effectiveness for image reconstruction in insufficient sampling problems. We successfully reconstructed CBCT images of superior accuracy from insufficient sampling data and evaluated the reconstruction quality quantitatively. Both simulation and experimental demonstrations of the CS-based reconstruction from insufficient data indicate that the CS-based algorithm can be applied directly to current dental CBCT systems for reducing the imaging doses and further improving the image quality.</P>
Je, U.K.,Cho, H.M.,Cho, H.S.,Park, Y.O.,Park, C.K.,Lim, H.W.,Kim, K.S.,Kim, G.A.,Park, S.Y.,Woo, T.H.,Choi, S.I. Pergamon 2016 Radiation physics and chemistry Vol.119 No.-
<P>In this paper, we propose a new/next-generation type of CT examinations, the so-called Interior Computed Tomography (ICT), which may presumably lead to dose reduction to the patient outside the target region-of-interest (ROI), in dental x-ray imaging. Here an x-ray beam from each projection position covers only a relatively small ROI containing a target of diagnosis from the examined structure, leading to imaging benefits such as decreasing scatters and system cost as well as reducing imaging dose. We considered the compressed-sensing (CS) framework, rather than common filtered-backprojection (FBP)-based algorithms, for more accurate ICT reconstruction. We implemented a CS-based ICT algorithm and performed a systematic simulation to investigate the imaging characteristics. Simulation conditions of two ROI ratios of 0.28 and 0.14 between the target and the whole phantom sizes and four projection numbers of 360, 180, 90, and 45 were tested. We successfully reconstructed ICT images of substantially high image quality by using the CS framework even with few-view projection data, still preserving sharp edges in the images. (C) 2015 Elsevier Ltd. All rights reserved.</P>
Kim, K.S.,Kang, S.Y.,Kim, W.S.,Cho, H.S.,Park, C.K.,Lee, D.Y.,Kim, G.A.,Park, S.Y.,Lim, H.W.,Lee, H.W.,Park, J.E.,Jeon, D.H.,Lim, Y.H.,Je, U.K.,Woo, T.H. BUTTERWORTH-HEINEMANN 2018 NDT AND E INTERNATIONAL Vol.98 No.-
<P><B>Abstract</B></P> <P>In conventional radiography, image visibility is often limited mainly due to the superimposition of the object’s structure under investigation and scattered x-rays. Several methods, including the antiscatter grid technique, the air-gap technique, and scatter correction methods using measurements, mathematical-physical modeling, or a combination of both, have been extensively investigated in an attempt to overcome these difficulties. However, these methods require special equipment, geometry, and extra work to measure the scatter characteristics. In this study, we propose a new image restoration method based on a simple radiographic scattering model in which the intensity of the scattered x-rays and the direct transmission function of a given object are estimated from a single x-ray image by using the dark-channel prior. We implemented the proposed algorithm and performed a systematic experiment by using a 450-kV industrial x-ray inspection system to demonstrate its viability for nondestructive testing. Our results indicated that the structure of the examined object was much more clearly visible in the restored image, considerably improving the radiographic visibility.</P>
Kim, K.S.,Park, S.Y.,Kim, G.A.,Cho, H.S.,Je, U.K.,Park, Y.O.,Park, C.K.,Lim, H.W.,Woo, T.H.,Park, S.M.,Lee, H.W.,Seo, C.W. Applied Science Publishers 2016 Optics and lasers in engineering Vol.86 No.-
In this work, we investigated a compressed-sensing (CS)-based deblurring scheme for image deblurring of high accuracy in digital tomosynthesis (DTS). We implemented the proposed deblurring scheme and performed a systematic simulation to demonstrate its viability for improved x-ray nondestructive testing. We also performed an experiment by using a table-top setup which consists of an x-ray tube (90kV<SUB>p</SUB>, 6mAs) and a CMOS-type flat-panel detector having a 198-μm pixel resolution. In both the simulation and the experiment, 51 projection images were taken with a tomographic angle range of θ=60<SUP>o</SUP> and an angle step of Δθ=1.2<SUP>o</SUP> and then deblurred by using the proposed algorithm before performing the common filtered-backprojection (FBP)-based DTS reconstruction. Our results indicate that the proposed deblurring scheme appears to be effective for the blurring problems in DTS and is applicable to improve the image characteristics in the present x-ray nondestructive testing.
Fernando, I.P. Shanura,Sanjeewa, K.K. Asanka,Samarakoon, Kalpa W.,Lee, Won Woo,Kim, Hyun-Soo,Kim, Eun-A,Gunasekara, U.K.D.S.S.,Abeytunga, D.T.U.,Nanayakkara, Chandrika,de Silva, E.D.,Lee, Hyi-Seung,Je The Korean Society of Phycology 2017 ALGAE Vol.32 No.1
Polysaccharides of marine algae exhibit different structural characteristics and interesting biological functions. In this study, crude polysaccharides (CP) of eleven Sri Lankan marine algae obtained through hot water extraction and ethanol precipitation were investigated for DPPH, alkyl, and hydroxyl radical scavenging activities using electron spin resonance spectrometry and for intracellular reactive oxygen species scavenging activity in the Chang liver cell line. Characterization of CPs was done by Fourier transform infrared (FTIR) spectroscopy and by analysis of the monosaccharide composition. Time-dependent density functional theory quantum-chemical calculations at the RB3LYP/6-31G(d,p) level for constructed dimeric units of the corresponding polysaccharides were used to resolve the FTIR spectra. CPs from Chnoospora minima showed the highest DPPH and alkyl radical scavenging activities and higher intracellular reactive oxygen species scavenging effects for both AAPH and $H_2O_2$ induced ROS production in "Chang" cells. The major polysaccharide constituent in C. minima CP was identified as fucoidan and it displayed a higher sulfate content. The degree of sulfation of these polysaccharides suggests a positive correlation with the observed antioxidant properties.
Je, U.,Kim, J.,Cho, H.,Lim, H.,Park, C.,Kim, G.,Park, S.,Park, Y.,Kim, K.,Woo, T.,Chung, N.,Kim, J.,Kim, J. Published for IMEKO by the Institute of Measuremen 2016 MEASUREMENT -LONDON- Vol.91 No.-
We have recently developed very precise carbon-interspaced antiscatter grids having a wide range of grid strip densities (i.e., 85-234lines/in.) by adopting the sawing process, depending on the demands of specific imaging modalities. However, because grid strips of the recently developed grids are mostly invisible through X-ray nondestructive testing due to their high strip densities, quality assurance in the manufacturing has not yet satisfactorily made. In this work, we proposed a pragmatic method to measure actual grid strip densities over the Nyquist sampling rate based on the moire pattern analysis. We prepared several samples of the carbon-interspaced grids having nominal grid strip densities of 85, 103, 130, 150, 178, 203, 215, and 234lines/in. and measured their strip densities by using the proposed method to demonstrate its viability assessment. The differences between the nominal and the measured grid strip densities were less than about 1.8%, indicating the proposed method is useful for the quality assurance in grid manufacturing.
D. K. Hong,S. H. LEE,조효성,J. E. Oh,M. S. Lee,김효정,Y. O. Park,U. K. Je,S. I. Choi,Y. S. Koo,H. M. Cho 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.11
In the paper, we proposed a pragmatic method capable of implementing a cost-effective, low-dose CT reconstruction directly onto a dental panoramic X-ray imaging system by adopting a spiral source trajectory. In the proposed geometry, a linear-type panoramic imaging sensor is rotated 90˚ from the orientation for panoramic imaging to imitate fan-beam image acquisition. For image reconstruction, we considered a total variation (TV) minimization-based algorithm that exploited the sparsity of the image gradient and was capable of reconstructing CT images with substantially high image accuracy against the image artifacts from sparse-view data. We implemented the algorithm for the proposed geometry and performed systematic simulation works to demonstrate its feasibility for dental imaging applications. CT images were successfully reconstructed from the proposed geometry, and the reconstruction quality was evaluated quantitatively by using an image similarity metric. We expect the proposed method to be applicable to developing a cost-effective, low-dose, all-in-one dental imaging system.