A Study on the Dynamic Range Performance Evaluation Method of Detector with Variation of Tube Voltage and Automatic Exposure Control (AEC) in Digital Radiography (DR) -Focused on the Dynamic Step Wedge and Histogram Evaluation

DR(Digital Radiography)에서 관전압 및 자동노출제어장치의 감도 변화에 따른 검출기의 동적 범위 성능평가 방법연구 -Dynamic Step Wedge와 히스토그램 평가를 중심으로

  • 황준호 (경희대학교병원 영상의학과) ;
  • 최지안 (경희대학교병원 영상의학과) ;
  • 김현수 (신구대학교 방사선과) ;
  • 이경배 (경희대학교병원 영상의학과)
  • Received : 2019.01.29
  • Accepted : 2019.02.20
  • Published : 2019.04.28


This study proposes a method to evaluate the performance of a detector by analyzing the dynamic step wedge and histogram according to the change of the tube voltage and sensitivity when using the Automatic Exposure Control (AEC). The performance of a detector was evaluated by measuring X-ray quality, Entrance Surface Dose (ESD), tube current, dynamic range corresponding to detector sensitivities of S200, S400, S800, S1000 per tube voltage of 60, 70, 81, 90 kVp. As a results, all of the qualities satisfied the acceptance criteria, and the Entrance Surface Dose and tube current were decreased stage by stage as sensitivity was set higher. In the dynamic step wedge, the observable dynamic range has also increased as tube voltage became higher. The histogram showed the quantization separation phenomena as the tube voltage was set higher. The higher the sensitivity, the more the underflow and overflow occurred in which the amount of information on both ends of the histogram was lost. In conclusion, the deterioration in the performance of the detector was found to be insufficient to realize the change of the tube voltage and sensitivity when using the Automatic Exposure Control, and it is useful to use dynamic step wedge and histogram in evaluating detector performance evaluation.

본 연구는 자동노출제어장치 사용 시 관전압과 감도 변화에 따른 dynamic step wedge와 히스토그램의 동적 범위 분석을 통해 검출기의 성능을 평가하는 방법을 제안하고자 하였다. 실험방법은 관전압 60, 70, 81, 90 kVp 별로 검출기 감도 S200, S400, S800, S1000에 해당하는 선질, 입사표면선량, 관전류량, 동적범위를 측정하여 검출기의 성능을 평가하고자 하였다. 그 결과 선질은 모두 합격 기준에 부합하였고, 입사표면선량과 관전류량은 감도가 높게 설정될수록 단계적으로 감소하였다. Dynamic step wedge는 관전압이 높아질수록 관찰 가능한 동적 범위도 함께 증가하였고, 또한 히스토그램은 관전압과 감도가 높게 설정될수록 양자화 이격 현상과 히스토그램 양단의 정보량이 상실되는 언더플로우와 오버플로우가 나타났다. 결론적으로 검출기가 성능 저하로 인하여 자동노출제어장치 사용 시 관전압과 감도 변화에 따른 동적 범위를 제대로 구현해내지 못한다는 것을 알 수 있었고, 검출기 성능평가 시 dynamic step wedge와 히스토그램을 통한 평가가 유용하다는 점을 알 수 있었다.


CCTHCV_2019_v19n4_368_f0001.png 이미지

그림 1. Primus A phantom

CCTHCV_2019_v19n4_368_f0002.png 이미지

그림 2. 다목적 선량계 MagicMax Universal과 Unfors Raysafe ThinX

CCTHCV_2019_v19n4_368_f0003.png 이미지

그림 3. Philips DIGITAL DIAGNOST VR(A)와 Philips DIGITAL DIAGNOST VR(B)의 dynamic step wedge 영상

CCTHCV_2019_v19n4_368_f0004.png 이미지

그림 4. 관전압 및 감도 변화에 따른 히스토그램

표 1. 방사선 발생장치와 관련된 특성

CCTHCV_2019_v19n4_368_t0001.png 이미지

표 2. 방사선 발생장치의 검사조건

CCTHCV_2019_v19n4_368_t0002.png 이미지

표 3. Philips DIGITAL DIAGNOST VR(A)의 백분율 평균 오차와 반가층

CCTHCV_2019_v19n4_368_t0003.png 이미지

표 4. Philips DIGITAL DIAGNOST VR(B)의 백분율 평균 오차와 반가층

CCTHCV_2019_v19n4_368_t0004.png 이미지

표 5. Philips DIGITAL DIAGNOST VR(A)의 입사표면선량의 평균과 표준편차

CCTHCV_2019_v19n4_368_t0005.png 이미지

표 6. Philips DIGITAL DIAGNOST VR(B)의 입사표면선량의 평균과 표준편차

CCTHCV_2019_v19n4_368_t0006.png 이미지


CCTHCV_2019_v19n4_368_t0007.png 이미지

표 8. Philips DIGITAL DIAGNOST VR(A)와 Philips DIGITAL DIAGNOST VR(B)의 동적 범위의 정성적 평가

CCTHCV_2019_v19n4_368_t0008.png 이미지


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