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X-선 스펙트럼 변화에 의한 CsI(Tl) 디지털 X-선 검출기 MTF의 에너지 의존성 평가

Estimation of Energy dependency for Modulation Transfer Function of CsI(Tl) Digital Radiography Sensor by X-ray Spectrum

  • 박민석 (Park, MinSeok, 대학원 보건과학과 방사선과학전공)

초록/요약

The Modulation Transfer Function (MTF) of radiography system have been widely used for evaluating the resolution and contrast of detecting system. Recently, Digital Radiography System and Detector are propagated for clinical usage. A method for acquiring the MTF has been devised to accurately measure the MTF of digital X-ray systems. However evaluation method for MTF was not considered the current characteristic of X-ray System and Sensor. Therefore, this research was measuring the MTF for variable radiation quality condition by the simulation and experimental study for evaluating the energy dependency of MTF through the progress which was suggested by IEC-62220-1 ("Medical electrical equipment _ Characteristics of digital X-ray image devices : Determination of the detective quantum efficiency" ,2000). For acquiring the MTF, in this research, a digital image of the edge is processed to obtain the presampled MTF. This Edge method has been compared to the slit method using measurements on standard and high-resolution imaging plates of a digital storage phosphor (DSP) radiography system. The edge method provides a convenient measurement of the presampled MTF for digital radiographic system with good response at low frequencies. In simulation result, the MTF data of RQA3 had higher value than other MTF of RQA5, RQA7, RQA9. Therefore, the result of MTF data for RQA3 was verified by the Two-sample test (t-test). The verification result showed that distinction between MTF data for RQA3 and other Radiation quality was not significance. The experimental study was performed by Digital Radiography System, Remote Radeye 200 sensor which was producted by Rad-icon imaging. Edge test device was used for acquiring the Edge spread function. The MTF result of each radiation quality showed the subequal trends of MTF curve. However, the MTF result via this progress was not accuracy and many experimental errors of X-ray system were generated. For this reason the simulation study for using Monte Carlo method, was also performed. In the simulation study, all condition of experiment were ideal and the result data were quantitatively calculated. Considering the results for both studies, however, MTF was a little influenced by radiation quality. Because CsI(Tl) sensor which was used for the Digital radiography system has low energy K-absorption edge. Therefore if the mean value of radiation energy was closed to the K-absorption edge of CsI(Tl) material, the effect of K-absorption edge was builded up. In conclusion, the radiation quality affect to the image resolution and contrast. Although the influence of radiation quality was not decisive, we might consider the effect of radiation energy to the sensor material for calculating the MTF.

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목차

제 1 장 서 론 1

1.1 연구 배경 1
1.2 연구 목적 2
1.3 논문 구성 3


제 2 장 이론적 배경 5

2.1 Digital Radiography System (디지털 X-선 영상 시스템) 5
2.2 Direct and Indirect 방사선 영상 검출기 7
2.3 Radiation Quality 9

2.4 방사선 영상의 해상특성 평가 10
2.5 MTF (Modulation Transfer Function) 12
2.5.1 MTF 산출 이론 12
2.5.2 Edge Spread Function Method 18
2.5.3 MTF 산출 시 Slit 및 Edge의 각도 20


제 3 장 MTF 산출 시뮬레이션 및 실험 방법 21

3.1 실험 재료 21
3.2 MTF 산출 시뮬레이션 방법 22
3.3 MTF 산출 실험 방법 25


제 4 장 MTF 산출 시뮬레이션 및 실험 결과 28

4.1 시뮬레이션을 통한 MTF 산출결과 28
4.1.1 Edge의 영상 및 Edge Spread Function과
Line Spread Function 28
4.1.2 각각의 RQA에 따른 Modulation Transfer Function 비교 31
4.2 실험을 통한 MTF 산출 결과 33
4.2.1 디지털 검출기를 이용한 Edge test device의 영상 및
Edge Spread Function 33
4.2.2 각각의 RQA에 따른 Modulation Transfer Function 비교 38


4.3 실험과 시뮬레이션을 통한 MTF의 산출 비교 평가 39


제 5 장 고 찰 42


제 6 장 결 론 44


참고 문헌 45

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