Earticle

기하학적 불선예도는 진단용 엑스선 영상의 공간분해능을 저하시키는 주요 요인으로, 본 연구는 초점 크기, 선원-검출기 간 거리(source-to-detector distance, SDD) 및 검출기 내 위치에 따른 공간주파수 특성을 정량적으로 분석하였다. 대면적 평판형 검출기를 이용하여 45 kVp에서 초점 크기(Small, Large), SDD(90, 110 cm), 검출기내 위치(Anode, Cathode, Upper, Lower)를 변수로 설정하였다. 폴리메타크릴산 메틸(poly-methyl methacrylate, PMMA) 엣지 및 균일 영상으로 각각 변조전달함수(modulation-transfer function, MTF)와 정규화된 잡음력스펙트럼(normalized noise-power spectrum, NNPS)을 산출하고, 손가락 팬텀의 residual 영상 분석을 병행하였다. SDD 증가에 따라 MTF는 향상된 반면 NNPS는 증가하는 경향을 보였으며, 동일한 SDD에서 초점 크기에 따른 MTF 차이는 크지 않았으나 NNPS에서는 차이가 관찰되었다. 위치별 MTF는 Upper와 Lower에서 높았고 Anode, Cathode 순이었으며, NNPS는 Anode에서 가장 높고 나머지 위치에서는 유사하였다. 이상의 결과는 엑스선 영상의 공간주파수 특성이 기하학적 촬영 조건과 검출기 내 위치에 따라 달라질 수 있음을 보여주며, 화질 최적화 시 이러한 공간적 변화를 함께 고려할 필요가 있음을 시사한다.

Geometric unsharpness is a major factor that degrades spatial resolution in diagnostic X-ray imaging. This study quantitatively evaluated spatial-frequency characteristics in relation to focal spot size, source-to-detector distance (SDD), and detector position. Experiments were performed using a large-area flat-panel detector at 45 kVp, with focal spot size (Small and Large), SDD (90 and 110 cm), and detector position (Anode, Cathode, Upper, and Lower) as variables. The modulation-transfer function (MTF) and normalized noise-power spectrum (NNPS) were derived from poly-methyl methacrylate (PMMA) edge and uniform images, respectively, with additional residual image analysis using a finger phantom. MTF increased with increasing SDD, whereas NNPS tended to increase. At the same SDD, MTF differed only slightly between focal spot sizes, whereas NNPS showed some variation. MTF was higher in the Upper and Lower regions, followed by the Anode and Cathode regions, whereas NNPS was highest in the Anode region and comparable across the remaining regions. These findings indicate that spatial-frequency characteristics may vary with both geometric imaging conditions and detector position, suggesting that such spatial variations should be considered when optimizing image quality.

To remove unnecessary background from tooth X-ray images and enhance the sharpness of tooth and gum images, image processing techniques including contrast adjustment and histogram equalization are used. The introduction of two methods for detecting the boundary of the tooth and gum region and separating the tooth and gum from the background. In both cases, the background of the tooth X-ray images could be removed as a result, improving the quality of the images. The proposed method improves MTF (Modulation Transfer Function), an image performance indicator, as a result of measuring MTF. The original image's spatial frequency ranged from 4.73 to 11.40 lp/mm at the 10% response, whereas the proposed image's spatial frequency ranged from 10.90 to 11.85 lp/mm, giving uniformly enhanced results. In contrast, tooth and gums could not be completely separated from the background using Apple's Lift subject from background function.

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.

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.