• Journal of Radiation Protection and Research
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• v.43 no.1
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• pp.1-9
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• 2018

Background: In this study, we investigate the image quality of virtual monochromatic images synthesized from dual-energy computed tomography (DECT) at voltages of 80/140 kV and 100/140 kV. Materials and Methods: Virtual monochromatic images of a phantom are synthesized from DECT scans from 40 to 70 keV in steps of 1 keV under the two combinations of tube voltages. The dose allocation of dual-energy (DE) scan is 50% for both low- and high-energy tubes. The virtual monochromatic images are compared to single-energy (SE) images at the same radiation dose. In the DE images, noise is reduced using the 100/140 kV scan at the optimal monochromatic energy. Virtual monochromatic images are reconstructed from 40 to 70 keV in 1-keV increments and analyzed using two quality indexes: noise and contrast-to-noise ratio (CNR). Results and Discussion: The DE scan mode with the 100/140 kV protocol achieved a better maximum CNR compared to the 80/140 kV protocol for various materials, except for adipose and brain. Image noise is reduced with the 100/140 kV protocol. The CNR values of DE with the 100/140 kV protocol is similar to or higher than that of SE at 120 kV at the same radiation dose. Furthermore, the maximum CNR with the 100/140 kV protocol is similar to or higher than that of the SE scan at 120 kV. Conclusion: It was found that the CNR achieved with the 100/140 kV protocol was better than that with the 80/140 kV protocol at optimal monochromatic energies. Virtual monochromatic imaging using the 100/140 kV protocol could be considered for application in breast, brain, lung, liver, and bone CT in accordance with the CNR results.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.2
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• pp.40-49
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• 1996

In this paper, we studied channel assignment and handover schemes for the indoor microcell systems. For efficient frequency spectrum reuse we proposed the high quality reassignment (HQR) scheme. Proposed HQR scheme tries to keep the reuse distances small by monitoring C/I of channels being used. To assign a channel for a new or handove call, the scheme checks C/I of all available channels. Then HQR assigns the channel that has C/I near the threshold value, A_TH. The scheme also checks C/I of ongoing calls and continuously reassigns a new channel when needed. It attempts handover not only when C/I gets below a handover threshold value, HO_TH, but also when C/I becomes above a high quality reassignment threshold, H_TH. The performance of the proposed HQR scheme was analyzed by a computer simulation configuraed. The performance of the scheme was also analyzed for various threshold values selected and the results are presented in this paper. The results show that HQR scheme perfomrs better than the scheme adopted for DECT.

• Proceedings of the Korea Information Processing Society Conference
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• 2002.11b
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• pp.1027-1030
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• 2002

본 논문에서는 제 3세대 이동 통신 시스템에서 안전한 전자상거래의 구현을 위한 인증 및 지불 메커니즘을 제안한다. 제 3세대 이동 통신 환경에서는 GSM이나 DECT와 같은 제 2세대 이동 통신 시스템에서 사용되지 못했던 공개키 기반 구조를 도입하여 각 이동 단말기 사이에 공개키 암호 시스템을 이용한 통신이 가능하게 되었다. 이동 사용자는 TTP(Trusted Third Party)로부터 획득한 공개키 인증서를 사용하여 외부 도메인에서도 종단간의 통신을 할 수 있으며 디지털 콘텐츠를 제공하는 사이트에 접속하여 안전한 서비스를 제공받을 수 있다. 본 논문은 이동 통신 환경에 적합한 소액지불 기법을 기반으로 하여 이동 사용자와 VASP간의 상호 인증 및 지불에 관한 기법을 제안한다.

• The Journal of Korean Society for Radiation Therapy
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• v.29 no.1
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• pp.77-84
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• 2017

Purpose: To evaluate the image quality improvement and dosimetric effects on virtual monochromatic images of a Dual Source-Dual Energy CT(DS-DECT) for radiotherapy planning. Materials and Methods: Dual energy(80/Sn 140 kVp) and single energy(120 kVp) scans were obtained with dual source CT scanner. Virtual monochromatic images were reconstructed at 40-140 keV for the catphan phantom study. The solid water-equivalent phantom for dosimetry performs an analytical calculation, which is implemented in TPS, of a 10 MV, $10{\times}10cm^2$ photon beam incident into the solid phantom with the existence of stainless steel. The dose profiles along the central axis at depths were discussed. The dosimetric consequences in computed treatment plans were evaluated based on polychromatic images at 120 kVp. Results: The magnitude of differences was large at lower monochromatic energy levels. The measurements at over 70 keV shows stable HU for polystyrene, acrylic. For CT to ED conversion curve, the shape of the curve at 120 kVp was close to that at 80 keV. 105 keV virtual monochromatic images were more successful than other energies at reducing streak artifacts, which some residual artifacts remained in the corrected image. The dose-calculation variations in radiotherapy treatment planning do not exceed ${\pm}0.7%$. Conclusion: Radiation doses with dual energy CT imaging can be lower than those with single energy CT imaging. The virtual monochromatic images were useful for the revision of CT number, which can be improved for target coverage and electron densities distribution.

• Archives of Reconstructive Microsurgery
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• v.3 no.1
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• pp.54-63
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• 1994

Pulp and palm of the hand and heel of the sole are anatomically unique. Satisfactory reconstruction of these areas presents the plastic surgeon with many challenges and requires durable and sensible skin coverage, minimal donor morbidity and reliable operative procedure. We presents 7 clinical cases of sensate instep free flap transfer in this paper during the last 2 years. Three cases were soft tissue defects due to crushing and avulsion injury on the pulp of finger. 1 case was unstable scar and redundant flap after reconstruction of soft tissue dect of palm and 1 case was contracture of first web of hand. One case was a soft tissue defect due to avulsion injury on heel. Lastly, one case was chronic osteomyelitis with open wound on lateral malleolar area. Follow-up period ranged from 3 months to 2 years. Through the whole follow-up period, all flaps were viable and durable to persistant stress or weight bearing and were sensible enough to porotect the recocstructed area from injuries and maintain functions. In conclusions, the instep free flap should be considered as a valuable tool in reconstruction of hand and extremity requiring durability and sensation.

• Nuclear Engineering and Technology
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• v.55 no.4
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• pp.1342-1349
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• 2023

The planning accuracy of charged particle therapy (CPT) is subject to the accuracy of stopping power (SP) estimation. In this study, we propose a method of deriving a pseudo-triple-energy CT (pTECT) that can be achievable in the existing dual-energy CT (DECT) systems for better SP estimation. In order to remove the direct effect of errors in CT values, relative CT values according to three scanning voltage settings were used. CT values of each tissue substitute phantom were measured to show the non-linearity of the values thereby suggesting the absolute difference and ratio of CT values as parameters for SP estimation. Electron density, effective atomic number (EAN), mean excitation energy and SP were calculated based on these parameters. Two of conventional methods were implemented and compared to the proposed pTECT method in terms of residuals, absolute error and root-mean-square-error (RMSE). The proposed method outperformed the comparison methods in every evaluation metrics. Especially, the estimation error for EAN and mean excitation using pTECT were converging to zero. In this proof-of-concept study, we showed the feasibility of using three CT values for accurate SP estimation. Our suggested pTECT method indicates potential clinical utility of spectral CT imaging for CPT planning.

• Journal of the Korean Society of Radiology
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• v.17 no.7
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• pp.1017-1023
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• 2023

The purpose of this study was to improve the accuracy of effective atomic number (EAN) and relative electron density (RED) using a polynomial-based calibration method using dual-energy CT images. A phantom composed of 11 tissue-equivalent materials was acquired with dual-energy CT to obtain low- and high-energy images. Using the acquired dual-energy images, the ratio of attenuation of low- and high-energy images for EAN was calibrated based on Stoichiometric, Quadratic, Cubic, Quartic polynomials. EAN and RED were extracted using each calibration method. As a result of the experiment, the average error of EAN using Cubic polynomial-based calibration was minimum. Even in the RED image extracted using EAN, the error of the Cubic polynomial-based RED was minimum. Cubic polynomial-based calibration contributes to improving the accuracy of EAN and RED, and would like to contribute to accurate diagnosis of lesions in CT examinations or quantification of various materials in the human body.

• Journal of Radiation Protection and Research
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• v.45 no.4
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• pp.171-177
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• 2020

Background: This study aims to determine the effective atomic number (Zeff) from dual-energy image sets obtained using a conventional computed tomography (CT) simulator. The estimated Zeff can be used for deriving the stopping power and material decomposition of CT images, thereby improving dose calculations in radiation therapy. Materials and Methods: An electron-density phantom was scanned using Philips Brilliance CT Big Bore at 80 and 140 kVp. The estimated Zeff values were compared with those obtained using the calibration phantom by applying the Rutherford, Schneider, and Joshi methods. The fitting parameters were optimized using the nonlinear least squares regression algorithm. The fitting curve and mass attenuation data were obtained from the National Institute of Standards and Technology. The fitting parameters obtained from stopping power and material decomposition of CT images, were validated by estimating the residual errors between the reference and calculated Zeff values. Next, the calculation accuracy of Zeff was evaluated by comparing the calculated values with the reference Zeff values of insert plugs. The exposure levels of patients under additional CT scanning at 80, 120, and 140 kVp were evaluated by measuring the weighted CT dose index (CTDIw). Results and Discussion: The residual errors of the fitting parameters were lower than 2%. The best and worst Zeff values were obtained using the Schneider and Joshi methods, respectively. The maximum differences between the reference and calculated values were 11.3% (for lung during inhalation), 4.7% (for adipose tissue), and 9.8% (for lung during inhalation) when applying the Rutherford, Schneider, and Joshi methods, respectively. Under dual-energy scanning (80 and 140 kVp), the patient exposure level was approximately twice that in general single-energy scanning (120 kVp). Conclusion: Zeff was calculated from two image sets scanned by conventional single-energy CT simulator. The results obtained using three different methods were compared. The Zeff calculation based on single-energy exhibited appropriate feasibility.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.655-662
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• 2016

We investigated on the usefulness of MAR algorithm by making a comparison of the CT value between before and after applying the MAR algorithm in dual energy CT, using the various kinds of medical metals, causing the artifact to lead to the low image quality. As a result, the artifact was reduced in most cases (P<0.05); in particular, the artifact was highly reduced (P<0.05) using high density material, like alloy-stainless (reduced by 78.1%) and platinum, for example GDC coil (reduced by 76.1%). The effect of decreasing the Black hole artifact was outstanding in both the alloy-stainless and alloy-titanium (P<0.05). However, in case of GDC coil-a type platinum, white streak artifact was reduced effectively (P<0.05). Therefore, in case of patients who have medical metals inserted, we think that high-quality image information can be provided by decreasing the artifact caused by high density material through MAR algorithm in dual energy CT.