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디지털 래디오그라피의 신호 및 잡음 특성에 대한 방사선 영향에 관한 연구
김호경,조민국,Thorsten Graeve 대한의용생체공학회 2007 의공학회지 Vol.28 No.6
For the combination of phosphor screens having various thicknesses and a photodiode array manufactured by complementary metal-oxide-semiconductor (CMOS) process, we report the observation of image-quality degradation under the irradiation of 45-kVp spectrum x rays. The image quality was assessed in terms of dark pixel signal, dynamic range, modulation-transfer function (MTF), noise-power spectrum (NPS), and detective quantum efficiency (DQE). For the accumulation of the absorbed dose, the radiation-induced increase both in dark signal and noise resulted in the gradual reduction in dynamic range. While the MTF was only slightly affected by the total ionizing dose, the noise power in the case of Min-RTM screen, which is the thinnest one among the considered screens in this study, became larger as the total dose was increased. This is caused by incomplete correction of the dark current fixed-pattern noise. In addition, the increase tendency in NPS was independent of the spatial frequency. For the cascaded model analysis, the additional noise source is from direct absorption of x-ray photons. The change in NPS with respect to the total dose degrades the DQE. However, with carefully updated and applied correction, we can overcome the detrimental effects of increased dark current on NPS and DQE. This study gives an initial motivation that the periodic monitoring of the image-quality degradation is an important issue for the long-term and healthy use of digital x-ray imaging detectors.
Characterization of CMOS Pixel Detectors for Digital X-Ray Imaging
Cho, Min Kook,Kim, Ho Kyung,Graeve, Thorsten,Kim, Jung Min Trans Tech Publications, Ltd. 2006 Key Engineering Materials Vol.321 No.-
<P>In order to develop a cost-effective digital X-ray imaging system, we considered a CMOS (complementary metal-oxide-semiconductor) photodiode array in conjunction with a scintillation screen. Imaging performance was evaluated in terms of MTF (modulation-transfer function), NPS (noise-power spectrum) and DQE (detective quantum efficiency). The presampled MTF was measured using a slanted-slit method. The NPS was determined by 2-dimensional Fourier analysis. Both the measured MTF and NPS, and a self-developed computational model for the X-ray spectral analysis were used to determine the spatial frequency-dependent DQE. From the measured MTF, the spatial resolution was found to be about 10.5 line pairs per millimeter (lp/mm). For a 45-kVp tungsten spectrum, the measured DQE around zero spatial frequency was about 40%.</P>
Measurements of X-ray Imaging Performance of Granular Phosphors With Direct-Coupled CMOS Sensors
Cho, Min Kook,Kim, Ho Kyung,Graeve, Thorsten,Yun, Seung Man,Lim, Chang Hwy,Cho, Hyosung,Kim, Jung-Min IEEE 2008 IEEE transactions on nuclear science Vol.55 No.3
<P> For <TEX>${\hbox {Gd}}_{2}{\hbox {O}}_{2}{\hbox {S}}{:}{\hbox {Tb}}$</TEX> granular phosphor screens having a wide range of mass thicknesses, we have investigated the fundamental imaging performance in terms of modulation-transfer function (MTF), noise-power spectrum (NPS) and detective quantum efficiency (DQE). As an optical photon readout device, a CMOS photodiode array with a pitch of 48 <TEX>$\mu{\hbox {m}}$</TEX> was used. Under the representative radiation quality, RQA 5, recommended by the IEC (International Electrotechnical Commission, Report 1267), the MTF was measured using a slanted-slit method to avoid aliasing and the NPS was determined by two-dimensional (2D) Fourier analysis of white images. The DQE was assessed from the measured MTF, NPS and the estimated photon fluence. Figure-of-merit (FOM) curves are presented to describe the tradeoff between the X-ray sensitivity and spatial resolution of screens as a function of mass thickness. This study will be useful for the selection guidance of <TEX>${\hbox {Gd}}_{2}{\hbox {O}}_{2}{\hbox {S}}{:}{\hbox {Tb}}$</TEX> phosphors for the relevant imaging tasks of digital radiography. </P>
( Esther Martinez-lombardia ),( Linsey Lapeire ),( Vincent Maurice ),( Iris De Graeve ),( Lorena Klein ),( Philippe Marcus ),( Kim Verbeken ),( Leo Kestens ),( Yaiza Gonzalez-garcia ),( Arjan Mol ),( 한국부식방식학회(구 한국부식학회) 2017 Corrosion Science and Technology Vol.16 No.1
When aiming for an increased and more sustainable use of metals a thorough knowledge of the corrosion phenomenon as function of the local metal microstructure is of crucial importance. In this work, we summarize the information presented in our previous publications[1-3] and present an overview of the different local (electrochemical) techniques that have been proven to be effective in studying the relation between different microstructural variables and their different electrochemical behavior. Atomic force microscopy (AFM)[1], scanning electrochemical microscopy (SECM)[2], and electrochemical scanning tunneling microscopy (EC-STM)[3] were used in combination with electron backscatter diffraction (EBSD). Consequently, correlations could be identified between the grain orientation and grain boundary characteristics, on the one hand, and the electrochemical behavior on the other hand. The grain orientation itself has an influence on the corrosion, and the orientation of the neighboring grains also seems to play a decisive role in the dissolution rate. With respect to intergranular corrosion, only coherent twin boundaries seem to be resistant.