The correlation between CT attenuations and tube current, tube voltage and iodine concentration as well as the percentage of reducing contrast agent volume while reducing tube voltage

Abstract

Objective To investigate the impact of tube current and tube voltage on CT attenuation, the correlation between CT attenuation and iodine concentration, as well as the percentage of reducing dosage for contrast agent while reducing the tube voltage. Methods A total of 100 saline solutions with decreasing dilution of contrast medium, in which concentration was between 0.5 to 50.0 mg/ml with the interval of 0.5 mg/ml, was produced. Each of the 25 syringes with a 4 ml sample was fixed on a cylindrical CT calibrated water phantom with an equal distance used the tape. CT scans were performed with a total of 15 scanning methods of the combination of the different tube voltages (70, 80, 100, 140 kV) and tube current (100, 200, 280 mA). All of the CT attenuations were measured and recorded. The differences of CT attenuations under different scanning tube currents and tube voltages were compared with one-way ANOVA. The Pearson correlation analysis was used to analyze the relationship between CT attenuation and iodine concentration, and linear correlation equations were calculated and shown by regression analysis. According to the equations, the changes of contrast medium dosage were calculated with the changes of tube voltage. Results There was no significant difference in CT attenuations on different tube currents when the tube voltage was fixed (all P>0.05), while when the tube current was fixed, the difference of CT attenuations on different tube voltages was statistically significant (all P<0.05). Under different scanning conditions, the CT attenuations was linearly related to the iodine concentration (r2 was 0.953 to 0.997, all P<0.01). While the tube voltage was reduced from 140 kV to 120 kV, 100 kV, 80 kV, 70 kV, respectively, the iodine concentration of the samples were reduced by 15.4%, 33.7%, 53.4%, 64.7% respectively. While the voltage was reduced from 120 kV to 100 kV, 80 kV, 70 kV, respectively, the iodine concentration were reduced by 21.6%, 44.9%, 58.2%, respectively. While the voltage was reduced from 100 kV to 80 kV and 70 kV, the iodine concentration was reduced by 29.7% and 46.7%, respectively. While the voltage was reduced from 80 kV to 70 kV, the iodine concentration was reduced by 24.1%. Conclusion CT attenuation can keep constant in low tube voltage setting by reducing the dosage of contrast agent, which can achieve a low radiation dose and low contrast agent dosage. Key words: Tomography, X-ray computed; Contrast media; Radiation dosage; Comparative study