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KMID : 1131320160180020023
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Journal of Korean Society of Computed Tomographic Technology
2016 Volume.18 No. 2 p.23 ~ p.39
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Radiation dose reduction and image quality assessment in neck CT using bolus shield
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Kim Yung-Kyoon
Kim Wan-Yuk
Kim Kwang-Soo
Byun Ji-Hye
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Abstract
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Purpose : This study aims to demonstrate the effectiveness with the comparison and evaluation of image quality and dose reduction effect for clinical usage protecting eye and thyroid with bolus in neck CT.
Materials and Methods : CT equipment which used in this study were GE VCT XTe 64 slice MDCT(General Electric medical systems, Milwaukee, USA) with Rando Phantom(model RAN-110, Churchin associate LTD, USA) and ACR Phantom(Model #438, Gammex TMI, USA).
For the protection of eye and thyroid, we used the latex (F&L Medical Products Co. 0.060 mmPb equivalent, USA) and Bolus (Eckert & Ziegler BEBIG Inc, Oxford, USA) covered bismuth. The parameters of standard protocol were 120 kVp, Noise Index 9.05, 100 ~ 300 mA, 2.5 mm thickness, pitch 0.984, and STD algorithm were set with AEC. Low dose protocol is adapted 100kVp and Fixed mA used as 200mA. The uniformity was evaluated by using ACR phantom program, and we evaluated CT number and noise of eye and neck area for using ADW 4.6(General Electric Healthcare, Barrington, USA) workstat ion. For the measurement of organ dose, it used fluoroglass dosimeter (GD-352M, 12 mm, FGD-1000 reader, Asahi Techno Glass Co, shizuoka, Japan). Program used in this study were PASW Statistics 18. Release 18.0.0 and Microsoft Office Excel 2007.
Results : As the result of assessment, low dose and standard protocol in bismuth group shows 12.58 and 12.17 highly. But, it was low as 1.16 ~ 2.42, 1.81 ~ 2.37 with 1, 2, 3 cm bolus(p<0.05). As the result of comparison evaluation on the SNR, noise, CT number in 5 groups (Non-shield, with Bismuth, with 1, 2, 3 cm Bolus) by T-test, showed significant differences on non-shield and Bismuth groups in standard and low-dose protocol regardless of AEC(p<0.05). But, the Bolus group didn t show the significant difference(p)0.05). CT number of organs depending on the thickness of the Bolus showed insignificant differences (5.73 HU) in applying AEC or not and each organs. Noise was increased with thickness, the differences were very slight 1.07 ~ 3.69 in eyeball(p<0.05), 0.14 ~ 2.09 in upper part of the neck, 0.06 ~ 2.86 in medial part of the neck, 0.14 ~ 2.19 in lower part of the neck. As the result of dose reduction, it shows the reduction of 26.1 ~ 34.7% of eye and 34.5 ~ 43.5% of thyroid in bismuth group. And it shows 9.2 ~ 26.53% eye dose and 6.6 - 28.9% thyroid in Bolus 1, 2, 3 cm attached.
Conclusion : In neck CT, the bolus shield is effective shield material because it rarely damage to the image quality with reducing thyroid and eye organ dose. Also bolus shield is very useful at 100 kVp area despite of 120 kVp in Adult without the adaptation of AEC.
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KEYWORD
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Neck CT, Bolus, Organ dose, Image quality
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