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KMID : 1131320160180010111
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Journal of Korean Society of Computed Tomographic Technology
2016 Volume.18 No. 1 p.111 ~ p.117
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Study for optimization of patient dose by changing Noise Index
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Kim Jin-Sook
Lee Ki-Baek
Kwon Seoung-Ohk
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Abstract
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Purpose : There are many techniques for reduction of patient dose from CT scan. In this study, we researched feasibility that can minimize patient dose preserving image quality by selecting Noise index according to weight of patients unlike former CT scans.
Materials and method : We classified patients into 4 groups using weight and NI steps in each chest and abdomen & pelvis CT subjects. Classification standards are whether weight of patient is above 70kg or not, how many NI steps were raised(1 or 2 steps). Control group is patients whose scans were performed with routine protocols for chest and AP part. Patients of each group are 35 and their average of patient dose was compared. IR 30% was applied to experimental groups. Image quality assessments were performed in same location using ROI. CNR and SNR were used as criteria of Image quality.
Result : In abdomen & pelvis CT less than 70kg, exposure dose, volume CT dose index (CTDIvol) was 12.79mGy, 10.23mGy, 8.53mGy and the variation of dose compared with routine protocol was decreased to 20% and 33%. The mean value of SNR was 83.1, 98.3, 87.7. Above 70kg, exposure dose was 17.3mGy, 17.21mGy, 15.81mGy and the variation of dose compared with routine protocol was decreased to 0.5% and 8.6%. The mean value of SNR was 78.7, 108.01, 81.8. In Chest CT less than 70kg, exposure dose was 8.59mGy, 6.8mGy, 6.26mGy and the variation of dose compared with routine protocol was decreased to 20% and 27%. The mean value of SNR was 91.4, 97.1, 96.6. Above 70kg, exposure dose was 12.6mGy, 12.28mGy, 11.41mGy and the variation of dose compared with routine protocol was decreased to 2.5% and 9.4%. The mean value of SNR was 90.3, 112.1, 100.6.
Conclusion : We could have dose reduction without loss of image quality by adjusting NI and applying IR. In this reason, if we adopt more subspecialized protocols and use dose reducing techniques, we can obtain high-quality image with optimized radiation dose.
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KEYWORD
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dose optimization, noise index, ASiR
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