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KMID : 1143620160200020021
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Korean Journal of Nuclear Medicine Technology
2016 Volume.20 No. 2 p.21 ~ p.26
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Metal artifact SUV estimation by using attenuation correction image and non attenuation correction image in PET-CT
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Kim June
Kim Jae-Il
Lee Hong-Jae
Kim Jin-Eui
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Abstract
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Purpose : Because of many advantages, PET-CT Scanners generally use CT Data for attenuation correction. By using CT based attenuation correction, we can get anatomical information, reduce scan time and make more accurate correction of
attenuation. However in case metal artifact occurred during CT scan, CT-based attenuation correction can induce artifacts and quantitative errors that can affect the PET images. Therefore this study infers true SUV of metal artifact region from attenuation corrected image count -to- non attenuation corrected image count ratio.
Materials and Methods : Micro phantom inserted 18F- FDG 4mCi was used for phantom test and Biograph mCT S(40) is used for medical test equipment. We generated metal artifact in micro phantom by using metal. Then we acquired both metal artifact region of correction factor and non metal artifact region of correction factor by using attenuation correction image count ?to- non attenuation correction image count ratio. In case of clinical image, we reconstructed both attenuation corrected images and non attenuation corrected images of 10 normal patient(66±15age) who examined PET-CT scan in SNUH. After that, we standardize several organs of correction factor by using attenuation corrected image count -to- non attenuation corrected count ratio. Then we figured out metal artifact region of correction factor by using metal artifact region of attenuation corrected image count -to- non attenuation corrected count ratio And we compared standard organs correction factor with metal artifact region correction factor.
Results: according to phantom test results, metal artifact induce overestimation of correction factor so metal artifact region of correction factors are 12% bigger than the non metal artifact region of correction factors. in case of clinical test, correction factor of organs with high CT number(>1000) is 8±0.5%, correction factor of organs with CT number similar to soft tissue is 6±2% and correction factor of organs with low CT number(-100>) is 3±1%. Also metal artifact correction factors are 20% bigger than soft tissue correction factors which didn`t happened metal artifact.
Conclusion : metal artifact lead to overestimation of attenuation coefficient. because of that, SUV of metal artifact region is
overestimated. Thus for more accurate quantitative evaluation, using attenuation correction image count -tonon attenuation correction image count ratio is one of the methods to reduce metal artifact affect.
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KEYWORD
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PET/CT, CT attenuation correction, metal artifact, 18F-FDG
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