Dose Modulation 기법에서 Noise Index 변화에 따른 선량 및 영상 Noise의 변화

Variation of Dose and Image Noise by Change of Noise Index

Purpose To evaluate the variation of exposure dose and image noise by change of noise index in a study of CT. Materials and methods 64 MDCT, Rando phantom, and photoluminescence dosimeter(PLD) were used for this study. We changed the noise index from 2 to 70 in phantom study with the same condition of abdominal CT, and then evaluated the variation of exposure dose(dose length product and organ dose) and value of image noise according to the noise index. Results In the variation of exposure dose, value of dose length product(DLP) was decreased to 33.3%, 35.5%, 30.3%, 26.2%, 24.3%, in changing from noise index 6 toward 8, 8 toward 10, 10 toward 12, 12 toward 14, 14 toward 16, respectively, and value of organ dose in liver was also decreased to 39.8%, 38.4%, 27.6%, 19.7%, 28.9%, in changing from noise index 6 toward 8, 8 toward 10, 10 toward 12, 12 toward 14, 14 toward 16, respectively. In the variation of image noise, the mean value and standard deviation was 7.01±1.21, 7.04±1.21, 11.29±1.18, 13.37±1.04, 15.66±1.13, 18.30±1.60, 20.19±1.49, in noise index 4, 6, 8, 10, 12, 14, 16, 18, respectively. Conclusion The variation of exposure dose was shown irregularly according to regular changing of noise index, and the most variation was between noise index 6 and 16 used in clinic mainly. The value of image noise was slightly higher than that of setting noise index in all measured range, the value of that between noise index 2 and 14 was constantly shown standard deviation with 1.5 and less.