• Korean Journal of Optics and Photonics
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• v.22 no.4
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• pp.161-169
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• 2011

In this paper, a tolerance allocation method using Monte-Carlo simulation with measured reflective eccentricity for high-sensitive IR optics is proposed. During optics fabrication and alignment, reflective eccentricity was measured using an optical centration measurement instrument. A Monte-Carlo simulation was performed using measured eccentricity data, and it gives statistical estimated performance of the optics after fabrication. The validity of the proposed tolerance allocation method was verified comparing the estimated MTF result with the measured MTF result of the fabricated optics.

• Journal of the Korean Society of Radiology
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• v.15 no.2
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• pp.173-179
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• 2021

Scattered x-ray generated by digital radiography systems also have the advantage of increasing signals, but ultimately detectability is reduced by decreasing resolution and increasing noise of x-ray images transmitted objects. An indirect method of measuring scattered x-ray in a modulation-transfer function (MTF) for evaluating resolution in a spatial-frequency domain can be considered as a drop in the MTF value corresponding to zero-frequency. In this study, polymethyl methacrylate (PMMA) was used as a patient tissue equivalent, and MTFs were obtained for various thicknesses to quantify the effect of scattered x-ray on resolution. X-ray image signals were observed to decrease by 35 ~ 83% with PMMA thickness increasing, which is determined by the absorption or scattering of x-rays in PMMA, resulting in reduced MTF and increased scatter fraction. The method to compensate for MTF degradation by PMMA resulted in the MTF inflation without considering the optical spreading generated by the indirect-conversion type detector. Data fitting or zero-padding are needed to compensate for MTF more reasonably on edge-spread function or line-spread function.

• Progress in Medical Physics
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• v.19 no.4
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• pp.219-226
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• 2008

In this study, we have conducted characterization of imaging performance for a flat panel digital X-ray detector using amorphous Selenium and a-Si TFT which was developed by the authors. The procedures for characterization were in concordance with internationally recommended standards such as IEC (international electrotechnical commission). The measures used for imaging performance characterization include response characteristic, modulation transfer function (MTF), detective quantum efficiency (DQE), noise power spectrum (NPS), and quantum limited performance. The measured DQEs at lowest and highest spatial frequencies were 40% and 25% respectively, which was superior to that of commercial products by overseas vendor. The MTF values were significantly superior to that of CR and indirect type DRs. The quantum limited performance showed the detector was limited by quantum noise at the entrance exposure level below 0.023 mR, which is sufficiently low for general X-ray examination.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.2
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• pp.203-209
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• 2013

Digital Radiography (DR) has improved a quality of resolution based on a wide dynamic range, high detective quantum efficiency (DQE), and modulation transfer function (MTF), compared with film/screen(F/s). Unlike expectation that a low level of radiation can be used in examination, high level of signal to noise ratio(SNR) due to over-exposure caused increase of exposed dose to patients. Also, the auto exposure control (AEC) using Kilovolage(kVp) in F/S can cause over-exposure. Hence, in this study, we proposed a proper method for using DR, in which effect of tubing Kilovolage on device's image, DR MTF measurement with changes of tubing current (mA), and the quantitative evaluation of skull phantom captured images' PSNR were evaluated. Changes of contrast with tubing Kilovolage can be improved by retouching, and MTF changes according to tubing current(1.41~1.39 lp/mm in 50% area, and 3.19~2.8 lp/mm in 10% area) does not influence on resolution of image. As a result, high tubing Kilovoltage, and tubing current will be suitable to use of DR.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.4
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• pp.323-335
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• 1992

In this paper, an adaptive cosine transform coding scheme which incorporate human visual properties into the coding scheme is investigated. Human vision is relatively sensitive to mid-frequency band, and insensitive to very low and very high frequency band. These property was mathematically modelled with MTF(Modulation Transfer Function) through many psychovisual experiment. DCT transforms energy in spatial domain into frequency domain, so can exploit the MTF very efficiently. Another well-known visual characteristics is spatial masking effect that visibility of noise is less in regions of high activity than in regions of low activity. Proposed coding scheme imploys quantization matrix which represent the properties of these spatial frequency response of human vision, and adaptively quality of an image. To compute the activity index of an image block, simple operation is performed in spatial domain, and according to activity index. block of low activity region is more exactly quantized relatively than that of high activity region. Results showed that, at low bit rate, the subjective quality of the reconstructed images by proposed coding scheme is acceptible than that of coding scheme without HVS properties.

• Journal of radiological science and technology
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• v.27 no.3
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• pp.25-29
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• 2004

Among the digital radiography systems, the computed radiography Image Plate Detector System is most frequently being used for the general radiography and also this system commonly diffracts the x-ray images since it is the system that is influenced by the light diffusion from the fluorescent substances. In this study, by using the X-ray Generator, a comparative analysis has been made between 2 different models of computer radiography image plate investigate each model's resolution and sharpness through the modulation transfer function(MTF) measurement. For the analysis, two image plates for general radiography one Fuji ST-VN model(more than 3years old) and one Fuji ST-VL model(less than 2years old) that are currently being used in "Hospital A" were sampled for the MTF measurement here. As the experimental method for this study, the resolution chart method has been carried out by using X-ray generator. Also all the experimental data were printed out by laser printer and measured by microdensitometer. As the results of the experiment carried out in this study, some differences have been found between the two different IP models and Fuji ST-VL has shown its excellence in both of the resolution and the sharpness fields.

• Journal of radiological science and technology
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• v.39 no.2
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• pp.193-198
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• 2016

In clinical computed tomography (CT), regular quality assurance (QA) has been required. This study is to evaluate the MTF for analyzing the spatial resolution using AAPM phantom in CT exam. The dual source somatom definition flash (siemens healthcare, forchheim, Germany), the brilliance 64 (philips medical system Netherlands) and aquilion 64 (toshiba medical system, Japan) were used in this study. The quantitative evaluation was performed using the image J (wayne rasband national institutes of health, USA) and chart method which is measurement of modulation transfer function (MTF). In MTF evaluation, the spatial frequencies corresponding to the 50% MTF for the CT systems were 0.58, 0.28, and $0.59mm^{-1}$, respectively and the 10% MTF for the CT systems were 1.63, 0.89, and $1.21mm^{-1}$, respectively. This study could evaluate the characteristic of spatial resolution of MTF using chart method, suggesting the quantitative evaluation method using the data.

• The Journal of the Korea Contents Association
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• v.16 no.7
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• pp.681-688
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• 2016

This study assess their quality of radiation on analysis of the spectrum of resolution suggesting IEC 61267 in radiation quality that RQA3, RQA5, RQA7, RQA9 and combination of clinical condition using several quality of radiation. In experiments edge method first, the spatial resolution assessment used image of the additional filter and SID is obtained the IEC 62220-1, spatial resolution and sharpness of the obtained image was evaluated in the MTF value 10%(0.1), MTF value 50%(0.5) using a Matlab program. Second, MCNPX simulation used spatial resolution analysis was radiation quality particle fluence and spectrum analysis in energy. As a result, make use of additional filter, image quality evaluation of SID that RQA3 radiation quality combination qualification is higher spatial resolution and sharpness make unused of additional filter and SID 100cm. RQA7 radiation quality combination qualification is higher that spatial resolution make unused of additional filter and SID 150cm. RQA9 radiation quality combination qualification is higher that spatial resolution and sharpness make used of additional filter and SID 180cm. spectrum analysis of radiation quality by reducing consequent errors occurring in the experiment that error due to the reproducibility of the X-ray tube, occur in an error of correction the detector suggest ideal conditions from spectrum analysis through MCNPX simulation. In conclusion, by suggesting spatial resolution and sharpness of result for various radiation quality, It provide basic data that radiation quality condition and quantitative assessment method for laboratory in clinical using detector evaluation.

• Progress in Medical Physics
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• v.23 no.3
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• pp.154-161
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• 2012

Digital Radiography (DR) has rapidly developed in megavoltage X-ray imaging (MVI). Thus, a very simple and general quality assurance (QA) method is required. The purpose of this study was to evaluate the modulation transfer function (MTF), the noise power spectrum (NPS) and the detective quantum efficiency (DQE) for MVI using general QA method and computed radiography (CR) device. We used tungsten edge block with $19{\times}10{\times}1cm^3$ thickness and 6MV energy. For detector, CR-IP (image plate), CR-IP-lead, the CR-IP-back (lanex TM fast back screen), CR-IP-front (lanex TM fast front screen) were used and pre-sampling MTF was calculated. The MTF of CR-IP-front showed the highest value with 1.10 lp/mm although the CR-IP showed the only 0.70 lp/mm. The best NPS was observed in CR-IP front screen. According to the increase in spatial frequency, our results showed that DQE was approximately 1.0 cycles/mm. The present study demonstrates that the QA method with our home-made edge block can be used to evaluate MTF, NPS and DQE for MVI.

• Aerospace Engineering and Technology
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• v.12 no.2
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• pp.30-39
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• 2013

In this study, calibration processes and methods of evaluating the radiometric quality of satellite images from the meteorological payload on the GEO-KOMPSAT-2A were described. MTF(Modulation Transfer Function), SNR(Signal-To-Noise Ratio), NEdT(Noise Equivalent Delta Temperature), and Dynamic Range, which are the major parameters for assessment of data radiometric quality of space-borne visible and infrared sensors, are focused. Key process of the quality check of the satellite data is the comparing the image radiometric performance parameters during the In-Oribit Test with those acquired from the ground tests. Validation plan of the image quality of the GEO-KOMPSAT-2A Meteorological Imager is addressed based on the analyses results of COMS MI data during the COMS In-Orbit Test period