Journal of the Korean Society of Radiology (한국방사선학회논문지)

The Korean Society of Radiology (한국방사선학회)
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The Effects of Image Quality due to Scattering X-ray according to increasing Patient Thickness

피사체 두께에 따른 산란선 발생이 화질에 미치는 영향

  • Park, Ji-Koon (Institute of Radiation Fusion Technology, International University of Korea) ;
  • Yang, Sung-Woo (Department of Radiological Science, International University of Korea) ;
  • Jun, Jae-Hoon (Department of Radiological Science, International University of Korea) ;
  • Cho, Su-Yeon (Department of Radiological Science, International University of Korea) ;
  • Kim, Kyo-Tae (Department of Biomedical Engineering, Inje University) ;
  • Heo, Ye-Ji (Department of Biomedical Engineering, Inje University) ;
  • Kang, Sang-Sik (Institute of Radiation Fusion Technology, International University of Korea)
  • 박지군 (한국국제대학교 방사선융합기술연구소) ;
  • 양승우 (한국국제대학교 방사선학과) ;
  • 전제훈 (한국국제대학교 방사선학과) ;
  • 조수연 (한국국제대학교 방사선학과) ;
  • 김교태 (인제대학교 의용공학과) ;
  • 허예지 (인제대학교 의용공학과) ;
  • 강상식 (한국국제대학교 방사선융합기술연구소)
  • Received : 2017.11.29
  • Accepted : 2017.12.31
  • Published : 2017.12.31
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Abstract

In this study, scattering factors affecting the quality of medical images were quantitatively analyzed and investigated. MCNPX simulation was conducted by using ANSI phantom, made of tissue equivalent materials, to calculate the scattering ratio occurred by the increase of the object thickness. Then, the result of the simulation was compared with the result of actual radiation measurement. In addition, we evaluated the image quality by the RMS evaluation, RSD and NPS analysis using X-ray images acquired with increasing object thickness. Furthermore, the scattering ratio was analyzed by increasing the thickness of acrylic phantom on chest phantom. The result showed that the scattering ratio was increased to 57.2%, 62.4%, and 66.8% from 48.9%, respectively, when the acrylic phantom thickness was increased by 1 inch from 6.1 inches. The results of MCNPX simulation and the actual measured scattering dose showed similar results. Also, as a result of RMS measurement from acquired x-ray images, the standard deviation decreased as the object thickness increased. However, in the RSD analysis considering the average incident dose, the results were increased from 0.028 to 0.039, 0.051, 0.062 as the acrylic phantom thickness was increased from 6.1 inches to 7.1 inch, 8.1 inch, and 9.1 inch, respectively. It can be seen that the increase of the scattering effect due to the increase of the object thickness reduces the SNR. Also, the NPS results obtained by measuring scattered radiation incident on the detector resulted in the increase of the noise as the object thickness increased.

본 연구에서는 피사체 두께 증가에 따른 산란선 발생이 의료 영상화질에 미치는 영향을 정량적으로 분석하기 위한 연구를 수행하였다. 기존 병원에서 검사빈도가 높은 흉부를 조직등가물질로 제작한 미국표준협회(ANSI; American National Standards Institute) 팬텀을 이용하여 피사체 두께가 증가함에 따라 발생하는 산란선 비율을 MCNPX 전산모사 하였으며, 실제 측정값과의 비교 분석을 수행하였다. 또한 피사체 두께 증가에 따라 획득된 X선 영상을 이용하여 RMS 입상성 평가, RSD 및 NPS 분석을 통해 산란선 발생 증가에 따른 화질 영향을 평가하였다. 흉부 팬텀위에 두께 1 인치의 아크릴 팬텀을 추가적으로 증가시키면서 분석한 결과, 표준 두께인 6.1 inch에서 산란선 비율은 48.9 %를 기준으로 1 인치 증가시마다 57.2 %, 62.4 %, 66.8 %로 증가하는 것으로 나타났으며, 이는 MCNPX 모의실험과 실제 측정한 산란선량은 유사한 결과를 보였다. 획득한 영상의 RMS 측정 결과, 피사체 두께가 증가함에 따라 표준편차가 낮아지는 값으로 도출되었다. 하지만 이를 평균 입사선량을 고려한 RDS 분석에서는 6.1 inch에서 0.028, 7.1 inch의 경우 0.039, 8.1 inch 경우 0.051 및 9.1 inch에서 0.062으로 증가하는 결과를 나타났다. 이는 피사체 두께 증가에 따른 산란선 발생 증가가 신호대 잡음비를 감소시킨다는 것을 알 수 있었다. 또한 검출기에 입사한 산란선 분포만 이용하여 측정한 NPS 결과에서도 피사체 두께가 증가할수록 노이즈가 증가하는 결과로 도출되었다.

Keywords

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