Earticle

본 연구에서는 ATS-539 다목적 초음파 팬텀을 이용하여 초음파 영상의 변조전달함수(Modulation-Transfer Function, MTF)를 분석하고, 임상 프리셋(THYROID, BREAST, APPE-L) 및 장비 설정 변수(Gain, Dynamic Range, Frame Average)의 변화가 영상의 공간 해상도에 미치는 영향을 정량적으로 평가하였다. 획득된 영상의 분석 결과, 중심 주파수가 높을수록 MTF 50% 값이 증가하여 세부 구조 재현성이 향상되는 경향을 보였다. 반면 Gain, DR, FA 변화에 따른 MTF 50% 값은 큰 차이를 나타나지 않았다. 또한 ATS-539 다목적 초음파 팬텀의 수직 방향 표적 분석 결과, 초점 영역이 형성된 근거리(상단) 위치에서 MTF 값이 높게 측정되어 깊이에 따른 공간 해상도 변화가 확인되었다. 이러한 결과는 초음파 영상 품질의 정량적 관리(Quality Assurance, QA) 및 장비 성능 검증의 표준화에 기여할 수 있으며, 초음파 영상의 진단적 품질 유지와 영상 최적화에 기여할 수 있을 것으로 기대된다.

In this study, the modulation transfer function (MTF) of ultrasound images was analyzed using the ATS-539 multi-purpose ultrasound phantom, and the effect of changes in clinical presets (THYROID, BREAST, APPE-L) and equipment setting variables (Gain, Dynamic Range, Frame Average) on the spatial resolution of images was quantitatively evaluated. As a result of analyzing the obtained images, the higher the center frequency, the higher the MTF 50% value, which tended to improve the detailed structure reproducibility. On the other hand, there was showed little variation in the MTF 50% value according to changes in Gain, DR, and FA. In addition, as a result of the vertical direction target analysis of the ATS-539 multi-purpose ultrasound phantom, the MTF value was measured high at the near (top) location where the focal area was formed, confirming the change in spatial resolution according to depth. These results are expected to contribute to the standardization of the quality assistance (QA) of ultrasound image quality and equipment performance verification, and to the maintenance of diagnostic quality of ultrasound images and image optimization.

본 연구에서는 변조전달함수(Modulation transfer function, MTF)를 이용한 컴퓨터 방사선영상의 감도 노출 분류에 따른 공간분해능을 평가하여 컴퓨터 방사선영상 획득의 기초자료로 제시하고자 하였다. 본 실험에서는 100 μmm 픽셀의 영상판을 이용하여 엣지법의 MTF를 측정하였다. 방사선 선질은 IEC 61267에서 권고하고 있는 RQA5를 이용하였다. X-선이 조사된 영상판은 감도 노출 분류를 50, 100, 200, 300, 400, 600, 800, 1200으로 각각 설정한 후 디지털 영상화하였다. 최종 획득된 영상들은 공인된 영상분석 프로그램인 image J와 Origin 8.0을 이용하여 MTF 50%와 10%를 구하여 평가하였다. 그 결과 감도 노출 분류 200에서 가장 우수한 MTF 50%(1.979 ± 0.114 lp/mm)와 MTF 10%(3.932 ± 0.041)의 공간주파수를 구하였다. 따라서 골절 등과 같이 높은 공간분해능을 요구하는 질병진단에 유용할 것으로 사료된다.

The purpose of the study was to present basic data to evaluation of the spatial resolution for exposure class(EC) in computed radiography(CR) by using the modulation transfer function(MTF). In this study, MTF was measured the edge method by using image plate(IP) of 100 μmm pixels. A standard beam quality RQA5 based on an international electro-technical commission(IEC) standard was used to perform the X-ray imaging studies. Digital imaging began to set the sensitivity to EC 50, 100, 200, 300, 400, 600, 800, 1200 in X-ray irradiated to IP. The MTF 50% and 10% in the final images was analysis by using an authorized image analysis program the Origin 8.0 and the image J. As a results, the EC 200 was the best spatial resolution at MTF 50% (1.979 ± 0.114 lp/mm) and MTF 10% (3.932 ± 0.041). Therefore, the EC 200 could be useful for the diagnosis of diseases that require high spatial resolution such as fractures.

The Modulation Transfer Function (MTF) is commonly used to characterize the spatial quality of imaging systems. This work is the attempt to measure the MTF at Nyquist frequency of the satellite imaging system what has 1m spatial resolution for KOMPSAT-2 image using the edge function. Artificial tarp targets are used in this study. A type of this tarp edge consists of two adjacent uniform bright and dark sides commonly used to test the performance of an optical system in edge function. The results from this work demonstrate the potential applicability of this method to estimate the response characteristics for KOMPSAT-2 that is scheduled to be launched.

The Modulation Transfer Function (MTF) is commonly used to characterize the spatial quality of imaging systems. This work is the attempt to measure the MTF for KOMPSAT EOC using the non-parametric method as ground inputs. The spatial performance of the KOMPSAT EOC was analyzed by edge method while in flight using multi-temporal image data collected over test site in Seoul. The results from this work demonstrate the potential applicability of this method to estimate MTF for high spatial resolution satellite KOMPSAT-2 that is being developed to be launched in 2005.

The dynamic modulation transfer function (MTF) for image degradation caused by sinusoidal vibration is formulated based on a Bessel function of the first kind. The presented method makes it possible to obtain an analytical MTF expression derived for arbitrary frequency sinusoidal vibration. The error obtained by the use of finite order sum approximations instead of infinite sums is investigated in detail. Dynamic MTF exhibits a stronger random behavior for low frequency vibration than high frequency vibration. The calculated MTFs agree well with the measured MTFs with the slant edge method in imaging experiments. With the proposed formula, allowable amplitudes of any frequency vibration are easily calculated. This is practical for the analysis and design of the line-of-sight stabilization system in the remote sensing camera.

The modulation transfer function (MTF) is a widely used indicator in assessments of remote-sensing image quality. This MTF method is also used to restore information to a standard value to compensate for image degradation caused by atmospheric or satellite jitter effects. In this study, we evaluated MTF values as an image quality indicator for the Geostationary Ocean Color Imager (GOCI). GOCI was launched in 2010 to monitor the ocean and coastal areas of the Korean peninsula. We evaluated in-orbit MTF value based on the GOCI image having a 500-m spatial resolution in the first time. The pulse method was selected to estimate a point spread function (PSF) with an optimal natural target such as a Seamangeum Seawall. Finally, image restoration was performed with a Wiener filter (WF) to calculate the PSF value required for the optimal regularization parameter. After application of the WF to the target image, MTF value is improved 35.06%, and the compensated image shows more sharpness comparing with the original image.

Purpose: This study was designed to investigate the effects of voxel size, the oversampling technique, and the direction and area of measurement on modulation transfer function (MTF) values to identify the optimal method of MTF measurement. Materials and Methods: Images of the wire inserts of the SedentexCT IQ phantom were acquired, and MTF values were calculated under different conditions(voxel size of 0.1, 0.2, and 0.3 mm; 5 oversampling techniques; simulated pixel location errors; and different directions and areas of measurement). The differences in the MTF values across various conditions were evaluated. Results: The MTF 10 values showed smaller standard deviations than the MTF 50 values. Stable and accurate MTF values were obtained in the 0.1-mm voxel images. In the 0.3-mm voxel images, oversampling techniques of 11 lines or more did not show significant differences in MTF values depending on the presence of simulated location errors. MTF 10 values showed significant differences according to the direction and area of the measurement. Conclusion: To measure more accurate and stable MTF values, it is better to measure MTF 10 values in small-voxel images. In large-voxel images, the proper oversampling technique is required. MTF values from the radial and tangential directions may be different, and MTF values vary depending on the measured area.

The performance of a staring infrared imaging system can be characterized based on estimating the modulation transfer function (MTF). The slant edge method is a widely used MTF estimation method, which can effectively solve the aliasing problem caused by the discrete undersampling of the infrared focal plane array. However, the traditional slant edge method has some limitations such as the low precision of the edge angle extraction and using the approximate function to fit the edge spread function (ESF), which affects the accuracy of the MTF estimation. In this paper, we propose a modified slant edge method, including an edge angle extraction method that can improve the precision of the edge angle extraction and an ESF fitting algorithm which is based on the transfer function model of the imaging system, to enhance the accuracy of the MTF estimation. This modified slant edge method presents higher estimation accuracy and better immunity to noise and edge angle than other traditional methods, which is demonstrated by the simulation and application experiments operated in our study.

The world's first geostationary ocean color imager (GOCI) is a three-mirror anastigmat optical system 140 mm in diameter. Designed for 500 m ground sampling distance, this paper deals with on-orbit modulation transfer function (MTF)measurement and analysis for GOCI. First, the knife-edge and point source methods were applied to the 8th band (865 nm) image measured April 5th, 2011. The target details used are the coastlines of the Korean peninsula and of Japan, and an island 400 meters in diameter. The resulting MTFs are 0.35 and 0.34 for the Korean East Coastline and Japanese West Coastline edge targets, respectively, and 0.38 for the island target. The daily and seasonal MTF variations at the Nyquist frequency were also checked, and the result is $0.32{\pm}0.04$ on average. From these results, we confirm that the GOCI on-orbit MTF performance satisfies the design requirements of 0.32 for 865 nm wavelength.

디지털 방사선 검출기의 성능을 측정하기 위해 변조전달할수(Modulation Transfer Function)을 측정하여 기존 방사선 영상 시스템인 필름/스크린과 비교하였다. 제작된 디지털 방사선 검출기는 TFT 패널위에 진공 증착법을 통해 비정질 셀레늄이 코팅되었다. 비교 측정물이 감도 400의 필름/스크린은 아날로그 방식의 방사선 검출기로서 현재 임상에서 이용되고 있는 필름이다. Square wave & slit 측정법을 통해 두 시스템의 변조전달함수를 측정하였다. 필름/스핀린의 반치폭(FWHM)은 357㎛(1.4 lp/mm at 50% spatial frequency)으로 측정되었으며, 디지털 방사선 검출 시스템은 200㎛(2.5 lp/mm at 50%)였다. 영상의 표현성능 평가의 결과 디지털 방사선 시스템은 필름 시스템보다 높은 것으로 나타났다.

To evaluate the performance of the digital radiography(DR) system developed in our group, the modulation transfer function(MTF) was measured and compared with that of an analog X- ray detector, film/screen system. The DR system has an amorphous selenium(a-Se) layer vacuum-evaporated on a TFT flat panel detector. The speed class 400 film/screen (Fuji) system has been being used in the clinical field as analog X-ray detectors. Both the square wave and slit method were used to evaluate their MTF. The square method was applied to both film/screen and the DR system. The slit method, however, was applied to only DR system. The full-width half maximum resolution of film/screen was 357${\mu}{\textrm}{m}$(1.4 lp/mm at 50% spatial frequency), and the resolution of DR was limited to 200${\mu}{\textrm}{m}$(2.5 lp/mm at 30%). These results indicate the measured resolution limitations approximate to the pixel pitch, 139 ${\mu}{\textrm}{m}$ of TFT. The MTF of DR is higher than that of film/screen by the factor of 1.785. It is proved that our a-Se based DR system has potential usefulness in the clinical field.

디지털 MTF의 정확도를 결정하는 요소로는 정확한 엣지 각도의 결정, 합성 ESF 또는 합성 LSF을 작성을 위한 재 샘플링, 스무징, 커브핏팅 등을 들 수가 있다. 본 실험에서는 Edge를 이용한 MTF커브 핏팅방법을 구현하였고, 슬릿법에 의한 MTF산출결과와 비교하였다. 실험결과 공간주파수 2.0 LP/mm 근방까지의 저주파수영역에서는 엣지법이 높은 수치를 나타내며 2.0 LP/mm 이상의 주파수 영역에서는 MTF값이 역전이 되어 슬릿법이 더욱 높은 값을 나타내었다. 이는 Cunningham의 보고와 완전히 일치한다.

Medical imaging zero-phase-sequence component in estimation for picture that is gotten that importance weight of digital device is increased day by day at the same time also so much important. Special quality about resolution uses Modulation Transfer Function by representative method to evaluate sharpness on important element in image quality. Get MTF converting slit, differentiating this making composition ESF edge method uses Excel by edge method in this study to be composition LSF get in fourier to informed measuring mean universally. Such method is considered that can help in principle grasping of step before make Program using C language as many as Matlab.

디지털 X선영상으로 출력한 화상데이터를 Personal Computer로 가져와서 디지털 특성곡선, MTF, 위너스펙트럼을 계산할 수가 있다. 여기서는 디지털화상의 선예도를 후지타(藤田) 등의 이론에 의한 프리샘플링(presampling) Modualtion Transfer Function(MTF)을 산출하고 보정하는 방법에 대하여 검토하였다. 사용한 프로그램은 엑셀이며 슬릿의 촬영, 디지털 특성곡선, 합성 LSF법, 이산 퓨리어 변환, 고속 퓨리어 변환 등의 순서로 기술하였다. 이 방법의 커다란 장점은 퓨리어트랜스폼의 공식과 MTF 산출과정을 완전히 이해할 수 있다는 점과, 별도로 값비싼 프로그램이나 컴퓨터언어를 배우지 않았어도 MTF 결과를 산출할 수가 있다는 것이다. 그리고 워크시트 표시되는 엑셀의 장점을 그대로 살려 X선 영상계의 오류나 산출결과의 부적합성을 발견하기 쉽다는 점이다.

By using CR image pixel data, We examined the way how to calculate the MTF and digital characteristic curve. It can be changed to the text-file(Excel) from a pixel data which was printed with a digital x-ray equipment. In this place, We described the way how to figure out and correct the sharpness of a digital images of the MTF from FUJITA. Excel program was utilized to calculate from radiography of slit. Digital characteristic curve, Line Spread Function, Discrete Fourier Transform, Fast Fourier Transform digital specification curve, were indicated in regular sequence. A big advantage of this method, It can be understood easily and you can get results without costly program and without full knowledge of computer language. It shows many different values by using different correction methods. Therefore we need to be handy with appropriate correction method and we should try many experiments to get a precise MTF figures.

본 연구는 간접평판형검출기(Indirect flat panel detector; FPD) 시스템 장비의 의료영상 품질 내용을 엣지법에 의한 위치에 따른 변조전달함수를 비교 분석하는 것이 목적이다. 간접 평판형 검출기(Indirect FPD) 방식의 Aero (Konica Minolta, Japan)를 사용하였다. 수용체의 크기는 14 × 17인치이며, 행렬 Matrix는 1994 × 2430 픽셀, 픽셀 피치(pixel pitch)는 175 ㎛이다. 국제전기기술위원회(IEC) 규격 기준으로 MTF를 측정하였고, 첫 번째 구역의 MTF 값이 0.1일 때 공간주파수 3.31 lp/mm, 두번째 구역의 MTF 값이 0.1일 때 공간주파수 3.81 lp/mm, 세 번째 구역의 MTF 값이 0.1일 때 공간주파수 4.31 lp/mm이었다. 또 다른 해석으로는 공간주파수 1.0 lp/mm일 때 MTF 값 0.61, 0.81, 0.83이었다. 결론적으로, 국제전기기술위원회(IEC)의 기준뿐 아니라, 실험 시 엣지의 각도 및 위치를 정확히 설정하고 구역별로 선정하여 MTF를 정량적으로 평가하는 것이 필수적이다. 따라서 본 논문의 결과는 엣지 각도 및 위치 선정 시 참고할 수 있는 유의미한 기준을 제시하며, 향후 관련 실험 설계에 있어 실질적인 도움이 될 것으로 사료된다.

The purpose of this study is to compare and analyze the modulation transfer function (MTF) according to edge position using the edge method, focusing on image quality in an indirect flat panel detector (FPD) system. An indirect FPD system, Aero (Konica Minolta, Japan), was used. The detector size was 14 × 17 inches, with a matrix size of 1994 × 2430 pixels and a pixel pitch of 175 ㎛. MTF was measured based on the standards of the International Electrotechnical Commission (IEC). When the MTF value was 0.1, the corresponding spatial frequencies were 3.31 lp/mm for the first region, 3.81 lp/mm for the second region, and 4.31 lp/mm for the third region. Alternatively, when the spatial frequency was fixed at 1.0 lp/mm, the corresponding MTF values were 0.61, 0.81, and 0.83, respectively. In conclusion, it is essential not only to comply with the IEC standards but also to accurately set the edge angle and position during experiments and to select regions systematically for quantitative evaluation of MTF. Therefore, the findings of this study provide meaningful reference data for selecting edge angle and position, and are expected to offer practical guidance for the design of future experiments.

임상적으로 computed tomography (CT)에서 정기적인 quality assurance (QA)는 요구되는 사항이다. 본 논문에서는 CT 검사에서 공간분해능에 대해서 AAPM Phantom을 이용하여 정확한 성능 분석을 위해 변조전달함수를 평가하고자 한다. CT장비는 dual source somatom definition flash (siemens healthcare, forchheim, Germany), brilliance 64 (phili ps m edi cal system N etherlands), a qui li on 64 (toshiba m edi cal system, Japan)를 사용하였으며, l mage J (wayne rasband national institutes of health, USA)프로그램을 실행하여 변조전달함수의 측정 방법인 chart method를 이용하여 영상에 대해서 정량적인 평가방법을 시행하였다. 변조전달함수를 이용하여 평가한 결과, 공간주파수를 이용한 데이터 값이 높아짐에 따라 변조전달함수는 감소됨을 알 수 있었다. 그리고 CT 장비에서 변조전달함수는 공간주파수(50%)에 있어서는 0.58, $0.28\;0.59mm^{-1}$으로 나타났으며, 변조전달함수 공간주파수(10%)에 있어서는 1.63, $0.89\;1.21mm^{-1}$으로 나타났다. 본 연구에서는 chart method를 이용하여 변조전달함수의 공간해상력에 대한 특성을 확인하고, 정량적인 평가방안을 제시하였다는 점에서 학술적 의의를 둘 수 있다.

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.

This study has investigated the relationship between heat release fluctuations and the flow perturbations in a partially premixed gas turbine combustor using a commercial CFD code. Special focus of the current work is placed on the effect of equivalence ratio on the flame dynamics in a partially-premixed system. As the first step for this combustion dynamics study in the non-perfectly premixed combustor, flame behaviors are modeled and then compared with measured results under both steady and unsteady conditions. The calculated results of the flame transfer function with equivalence ratio fluctuation are found to well capture the main qualitative characteristics of the combustion dynamics for the partially-premixed flames.