Objective        To evaluate the effect of different tube voltage and noise index on radiation dose of different body thickness in phantom using tube current automatic regulation technology.       Methods        Home-made cone phantom was used for segmental scanning in order to simulate patients with different body thickness. Using tube current automatic regulation technology

the noise index (10-20) and tube voltage (80-140 kV) were

adjusted

respectively

and volume computed tomography dose index (CTDIvol) was recorded.       Results        When the average body thickness was less than 126.2 mm

CTDIvol was the lowest either the noise index was 10-12 and tube voltage was 80 kV or the noise index was 12-20 and tube voltage was 120 kV. When the average body thickness was not less than 126.2 mm

CTDIvol was the lowest if the noise index was 10-20 and tube voltage was 120 kV. The regression equation was established: CTDIvol=0.511+0.081 thickness-0.709 (noise index)+0.004 voltage. The coefficients of overall model

body thickness and noise index were all tested (

P

0.001)

and the coefficients of distance and voltage were also analyzed (

P

=0.487

0.415).       Conclusion      Using tube current automatic regulation technology

the radiation dose (CTDIvol) increases with the increase of the phantom thickness

and decreases with the increase of the noise index. Although there is no significant correlation between CTDIvol and tube voltage

the radiation dose can be reduced by using tube voltage of 120 kV within the range of adult body thickness.