Objective To assess the feasibility of using an automatic tube current modulation (ATCM)method to obtmn consistent image quality with reduced radiation dose for young children undergoing chest scans with a set of 64-slice spiral CT.Methods Fifry young children underwent chest scans on a GE 64-slice VCT with automatic tube current modulation.The noise index(NI)for this study group was set to 8 or 9 based on the proposed reference for pediatric chest imaging in our hospital.We compared image quality and radiation dose for the study group with the age-matched control group of 50 young children acquired with standard protocol of fixed-mAs(120 and 150 mAs for under 1 and above 1 year old,respectively).The volume CT dose index(CTDIvol)values were recorded for beth groups.Two experienced pediatric radiologists assessed image quality on a 5-point scale with 5 being the best.Scores greater than or equal to 3 were considered clinically acceptable.The degree of interobserver concordance was determined by Kappa statistics.Results The average objective image noise and CTDIvol for control group was(4.78±0.58)and(6.68±0.62)mGy,respectively.For the study group the mean value of objective mAs wag(41.6±11.6)(20-79 mAs)with mean CTDIvol of(2.34 4±0.71)mGy,and the use of ATCM produced mean noise of(7.84±0.66).The average CTDIvol with the use of NI of 8-9 was about 65% lower than that with the fixed mAs setting.The mean image quality score for the study group and control group was(3.46±0.40)and(4.65±0.46)respectively.All studies had acceptable image quality,and there was good inter-observer agreement in diagnostic acceptability(Kappa=0.474 and 0.536).Conclusion The automatic tube current modulation method could be used to obtain consistent image qualityfor young children undergoing 64-slice MSCT chest scans.With proper noise level setting(NI=8 or 9),one may obtmn clinically acceptable images with much reduced radiation dose.