Objective To investigate the effects of X-ray beam hardening from contrast agent on CT values on CTA images.Methods The 20 mL syringes were numbered 1 to 26.The syringe 1,4,7,23 and 20 were filled with 1 mL,0.8 mL,0.6 mL,0.4 mL and 0.2 mL of iodine contrast medium (300 mg I/mL),respectively,and then mixed each of them with 0.9％ NaC1 solution to get a total of 20 mL solution in each syringe.The rest of 26 syringes were filled with 20 mL of 0.9％ NaC1 solution,as the experimental group to simulate carotid artery CTA examination.Matched 26 numbered syringes were filled with 20 mL 0.9％ NaC1 solution respectively,as control group to simulate plain scan.CT scans were performed,CT values were measured,and then the difference of CT values of 0.9 ％ NaCl solution in two groups was analyzed statistically.Results The mean,maximum and minimum CT values of saline in the experimental group vs control group were (-0.139±10.322) HU vs (5.585±2.939) HU,14.6 HU vs 9.7 HU,-23.8 HU vs-2.4 HU,respectively,and the differences were significant (t=2.695,P＜0.05).The CT values of saline around the high concentrations of iodine solution showed a large fluctuation range.Conclusion The X ray beam hardening effects caused by high concentration of iodine contrast on carotid artery CTA phase,may cause significant fluctuations of CT values.