The Influence Of Tube Voltage In Computed Tomography On The Image Quality, Physical Radiation Dose And Biological Effect

PART ONE: Impact of tube voltage protocols on CT image quality at the same physical radiation dose: phantom studyObjective: To evaluate the impact of tube voltage protocols on CT image quality at the same physical radiation dose.Materials and Methods: Different protocols of 80 k V, 100 k V, 120 k V and 140 k V at three physical radiation dose levels(5m Gy, 10 m Gy, 15 m Gy) were selected by dosimeter. A Catphan 600 phantom was scanned by a scanner(GE Lightspeed VCT) and Image quality was assessed with following aspect: high density resolution, low density resolution and image noise(SD).Results(1)The same high density resolutions of 6 lp/cm were achieved at 5mGy, 10 m Gy and 15 m Gy level.(2) The low density resolutions at 5m Gy, 10 m Gy and 15 m Gy level were 6mm@1%, 4mm@1% and 2mm@1%, respectively. The low density resolutions were same at each level,but different among the three levels.(3) The SD among the three radiation levels were 14.06±1.01Hu、10.51±0.89 Hu and 7.94±0.92 Hu respectively, with significant statistical difference(P<0.001), but there were no statistical differences of image noise(P>0.05) at each level.Conclusions: There are no significant differences in CT image quality with different tube voltage protocols at the same physical radiation level. The higher physical radiation dose we used, the higher low density resolution and image noise we got.PART TWO: The influence of tube voltage in computed tomography on the DNA damage in human peripheral blood mononuclear cells at the same physical radiation dose: an experimental studyPurpose: To investigate the DNA damage in human peripheral blood mononuclear cells after CT scans at different tube voltages by γH2AX–based fluorescence immunoassay, an in vitro study.Materials and Methods: Sixteen people were recruited prospectively; After written informed patient consent were obtained, blood samples were taken from the antecubital vein of all volunteers, and collected into vacuum tubes containing lithium heparin. The blood samples(in tubes) from each volunteer were exposed to different preset groups with GE Light Speed VCT scanner placed in center of a tissue equivalent abdomen phantom. 5 minutes later, blood samples were isolated, fixed, and stained for γH2AX expression. The γH2AX focus yields were determined with fluorescence microscopy. Data were analyzed by using One-way analysis of variance(containing pairwise multiple comparison procedures), linear correlation method.Results: The number of γH2AX focus in human PBMCs increase linearly with CT dose following different tube voltages(80, 100, 120, 140 k V), and the coefficient of determination(R2) are 0.9804, 0.9757, 0.9653, 0.9516. The γH2AX focus yields are not exactly the same between the scanning groups(P<0.05). The pairwise multiple comparison procedures show that there are significant difference between the 140/120 k V and 80 k V groups,which means the number of γH2AX focus in 80 k V are much more than 140/120 k V(P<0.05).Conclusion: The γH2AX focus yields in human PBMCs increase highly linear correlation with CT dose. The DNA damage of PBMCs after CT using 140-k V are much lightly than 80-k V with the same CT dose.