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KMID : 1131320160180020107
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Journal of Korean Society of Computed Tomographic Technology
2016 Volume.18 No. 2 p.107 ~ p.113
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The Comparison and Evaluation of Image quality according to Pitch Change and applying to Double-Z Sampling Technifque with same Hardware of Corporation
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Kang Jung-Ho
Seo Beom-Jong
Lee Sook-Hee
Im Heung-Sun
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Abstract
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Purpose : We tried to compare image quality by measuring noise value using pitch change and applying to Double-Z Sampling technique with 2 CT modalities which are consist of same hardware of same corporation.
Materials and Methods: We used AAPM CT performance phantom (Nuclear Associates, Model 76-40), Brilliance 64 CT (Philips Healthcare, Netherlands) and Ingenuity 128 CT(Philips Healthcare, Netherlands).
On phantom study, All the parameters like CTDI value are same except pitch value. We measured average and standard deviation value by using ROI analyzing function of PACS after setting 4 x 4 cm sqaure on 1/4 spot from the center of noise measurement block of AAPM phantom towards 6 o clock position.
On clinical study, 30 patients who have taken Low-dose screening chest follow-up CT were chosen for this study applying to the same protocol as Low-dose chest CT in our hospital from January 2015 to December 2015. We applied different pitch values to 2 CT modalit ies. Brilliance 64 CT was 0.516 (Group1) and Ingenuity 128 CT was 1.048 (Group2). And we also set 36mm² of same ROI using ROI analyzing function of PACS and measured noise value of lung nearby rib cage and costal margin on thin section coronal plane.
Statistical analysis was used to Wilcoxon signed rank Test of SPSS program(Inc. Chicago) in order to verify statistical significance of noise value measured by two groups.
Result : In case of phantom study, noise value measured in Ingenuity 128 CT showed us average 5.31. It was higher than noise level measured in Brilliance 64 CT which was average 4.83. In case of clinical study, noise value of Group 1 was average 26, standard deviation 4.79 and Group 2 was average 28.86, standard deviation 6.67.
As a result of Wilcoxon Signed Rank Test, P-value was 0.006 and statistically significant on the comparison of noise value between Group 1 and Group 2.
Conclusion : Through this study, we found that the change of noise value showed us a few difference as pitch value increase. that is to say, noise value increase as scan hardware data acquisition following Double-Z sampling technique increase. But, it’s quite small difference that it can’t affect image quality. So we think that using Double-Z sampling is clinically useful due to advantage of getting double data acquisition.
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KEYWORD
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Double Z-Sampling, Z-flying focal spot, Pitch, Noise
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