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KMID : 1131320160180020059
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Journal of Korean Society of Computed Tomographic Technology
2016 Volume.18 No. 2 p.59 ~ p.72
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The dose reduction effect and image quality evaluation of lens and Thyroid by using ODM and bismuth
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Lee Seung-Hyun
Oh Hyun-Sik
Kim Wan-Yuk
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Abstract
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Purpose : It is to know the method of the limiest dose reduction of lens and Thyroid which is comparative high sensitivity with the implementation of the best images during head and neck exam by using ODM(Organ Dose Modulation, ODM) that is AOBCM(automated organ current modulation) by GE manufacture company, AEC(Automatic exposure control) and bismuth.
Materials and Methods : CT equipment is used Discovery CT 750HD(General Electric Medical System, Milwaukee, Wisconsin USA), and Alderson Rando phantom(CNMC Company, USA) is used with attached Radiophoto Luminescent Glass Dosimeter five to head and six to neck for dose measurement using tour methods(AEC, ODM, bismuth, ODM+bismuth) with 10 times scan and acquired average value. Also to evaluate image quality, we used noise and CT number, and to measure linearity and uniformity by using ACR phantom (Model #438, Gamex RMI, USA). Statistic is used MedCalc version 16.1 to have average and standard deviation of all measurement values, and it could be judged statistically when p-value under 0.05 by AVOVA test.
Result : The standard by the usage of AEC, the measured dose result shows that lens were ODM 19.2%, bismuth 32.9%, ODM and bismuth 46.7% down, and to Thyroid shows that ODM 31.2%, bismuth 24.9%, ODM and bismuth 56.8% down. To evaluate image quality for noise, lens shows that ODM 7.1 %, bismuth 17.7%, ODM and bismuth 13.3% increase, to Thyroid shows that ODM 10.1 %, bismuth 30.0%, ODM and bismuth 36.9% increase, for CT number values, lens show that ODM 0.3%, bismuth 50.0% and ODM+bismuth 48.8% increase, to Thyroid shows that ODM 1.9% down, bismuth 296.2%, ODM and bismuth 305.8% increase. To evaluate using ACR phantom, for the usage of bismuth, linearity and uniformity were out of tolerance field recommended ACR because of artifact, by ODM case was under tolerance field for ACR recommendation. To judge statistical significance test, as the result of dose, noise and CT number values by ANOVA test, we confirmed that all results were significant with p-value< 0.05.
Conclusion : When using ODM, it was known that dose could be reduced over 25% and increased noise, but continued CT number. Also, neck which is lower thickness compared head shows low noise changes and CT number values continuation. Through this result, it is considered that ODM is more effective method for dose reduction and image quality to less thickness area.
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KEYWORD
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ODM, AOBCM, Orbit, Thyroid
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