Journal of the Korean Society of Radiology (한국방사선학회논문지)

The Korean Society of Radiology (한국방사선학회)
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The Effect of Grid Focus Distance on Patient Dose, Exposure Index, and Image Quality in Digital Abdominal Radiography

격자의 초점거리가 디지털 복부 방사선검사의 환자선량 및 노출지수 그리고 영상 품질에 미치는 영향

  • Young-Cheol Joo (Department of Radiology, Samsung Medical Center) ;
  • Sin-Young Yu (Department of Radiological Technology, Donggang University)
  • 주영철 (삼성서울병원 영상의학과) ;
  • 유신영 (동강대학교 방사선과)
  • Received : 2024.10.15
  • Accepted : 2024.10.31
  • Published : 2024.10.31
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Abstract

The purpose of this study is to investigate the effect of differences in grid focal distance used in general radiography on the exposure index and image quality, and to provide useful information for the application of grids in clinical radiography. With AEC applied and SID set to 110 cm, 30 images were obtained for each focus distance of the grid at 110 cm, 140 cm, and 180 cm under the same exposure conditions. The dose was measured using the DAP and ESD, while image quality was evaluated using the SNR and CNR. The exposure index (EI) was determined based on the values shown in the image. EI was derived from the values indicated in the images. The mean DAP values at focus distances of 180, 140, and 110 cm were 10.944±0.613, 10.687±0.516, and 9.74±0.588 cGy·cm2, respectively. The ESD values were 1041.75±57.92, 1019.99±49.61, and 930.86±55.77 μGy, while the EI values were 205.97±11.77, 210.59±10.37, and 193.8±11.86. The SNR values were 28.48±0.62, 28.41±0.64, and 27.13±0.72 dB, and the CNR values were 0.09859±0.004276, 0.09864±0.004378, and 0.09026±0.004783 dB. The differences in the mean values were statistically significant (p < 0.01). The values were significantly higher at focal distances of 140 cm and 180 cm compared to 110 cm, but there was no significant difference between the focal distances of 140 cm and 180 cm. The correlation analysis results revealed significant negative correlations between FD and DAP (r = -0.642, p < 0.01), ESD (r = -0.629, p < 0.01), EI (r = -0.376, p < 0.01), SNR (r = -0.615, p < 0.01), and CNR (r = -0.575, p < 0.01) for all variables. The results of this study showed a moderate negative correlation between the focus distance of the grid and the SNR, CNR, DAP, and ESD, and a weak negative correlation with the EI. Therefore, radiological technologists should be aware that even when the same exposure conditions are applied using an AEC system, variations in focus distance of the grid can affect the exposure index, dose, and image quality. Careful consideration is needed when setting the target exposure index.

본 연구의 목적은 일반 방사선검사 시 사용되는 격자의 초점거리 차이가 노출지수와 영상의 품질에 미치는 영향을 알아보고, 임상에서 방사선검사를 위해 격자 적용 시 유용한 정보를 제공하는 데 있다. AEC 적용 후 SID 110 cm로 설정하고, 동일한 노출 조건에서 격자의 초점거리(110 cm, 140 cm, 180 cm) 별로 격자를 변경하여 각 30개의 영상을 획득하였다. 선량은 면적선량과 입사표면선량을 측정하였고, 영상 품질은 신호 대 잡음비와 대조도 대 잡음비로 평가하였다. 노출지수(EI)는 영상에서 나타난 수치를 이용했다. 획득한 자료는 정규성검정 후 일원배치분산분석(사후분석 Duncan)을 통해 평균비교분석을 실시하였으며, Pearson 상관분석을 통해 독립변수와 종속변수의 상관성을 분석하였다. 초점거리 180, 140, 110 cm의 DAP 평균값은 10.944±0.613, 10.687±0.516, 9.74±0.588 cGy×cm2이었고, ESD는 1041.75±57.92, 1019.99±49.61, 930.86±55.77 μGy, EI는 205.97±11.77, 210.59±10.37, 193.8±11.86 이었으며, SNR은 28.48±0.62, 28.41±0.64, 27.13±0.72 dB, CNR은 0.09859±0.004276, 0.09864±0.004378, 0.09026±0.004783 dB이었다. 각 평균값의 차이는 통계적으로 유의한 차이가 있었다(p<0.01). 초점거리 110 cm 보다 유의미하게 초점거리 140 cm와 180 cm에서 높게 나타났으나 초점거리 140 cm와 180 cm의 차이는 없는 것으로 나타났다. 상관관계 분석 결과 FD와 DAP(r=-0.642, p<0.01), ESD(r=-0.629, p<0.01), EI(r=-0.376, p<0.01), SNR(r=-0.615, p<0.01), CNR(r=-0.575, p<0.01)의 모든 변수에서 유의미한 음의 상관관계가 나타났다. 본 연구의 결과 격자의 초점거리는 신호 대 잡음비와 대조도 대 잡음비, 면적선량과 입사표면선량과는 중간정도 음의 상관관계가 있었고, 노출지수와는 약한 음의 상관관계가 있는 것으로 나타났다. 그러므로 방사선사는 자동노출조절장치를 이용한 방사선검사 시 동일한 조사조건을 적용해도 격자의 초점거리에 따라 노출지수 및 선량, 영상의 품질에 변화가 발생할 수 있음을 인지하고, 목표 노출지수 설정 시 유의할 필요가 있다고 사료 된다.

Keywords

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