Preliminary study of X-ray dosage reduction using post-processing filter in 64-slice spiral CT cardiac examination

Abstract

Objective To evaluate the adaptive post-processing filter(C_2)on reducing X-ray dosage in 64-slice CT cardiac examinations.Methods The study was divided into two steps:(1)On 30 consecutive patients(group A)prescribed for cardiac scans on 64-slice CT,the scan protocol was 120 kV,640 mA,0.35 s/r,0.625 mm slice thickness,0.22—0.24 pitch and large body bowtie.For each patients,cardiac images were reconstructed with and without C_2 filter to create two image sets(C_2 and NC_2, respectively).The image quality was blindly evaluated between C_2 and NC_2.Image noises were also measured and their means and standard deviations calculated for the two sets.Statistical t-test analysis was performed on the quality scores and the noise between the two data sets.(2)On the 30 consecutive cardiac patients in another group(group B),the protocol was kept the same as in group A except for decreasing the tube current 450 mA based on the results from group A.Images were reconstructed using post-processing filter C_2 to create 2C_2 image set.Statistical t-test was performed between image sets of 2C_2 and NC_2 in step 1.(3)CTDIvol values from the 2C_2 and NC_2(C_2)groups were converted into effective dose(ED)and the ED values of the two groups were compared.Results(1)The image quality scores for the C_2 and NC_2 sets were 3.71±0.31 and 3.72±0.29,respectively,with t-test of P0.05,indicating no significant statistical difference(P0.05).The noise of C_2 and NC_2 sets were 22±4、27±5,respectively,indicating the difference was statistically significant(P0.01).The noise with C_2 filter had 18% noise reduction compared to those without C_2 filter.(2)The image quality scores for the 2C_2 and NC_2 sets were 3.67± 0.34,3.72±0.29,indicating no significant statistical difference(P0.05).The noise of 2C_2 and NC_2 sets were 26±3,27±5,indicating no significant statistical difference(P0.05).(3)The average CTDIvol values were 60±5 mGy,88±10 mGy for 2C_2 and NC_2(C_2)groups,respectively.The corresponding ED values were(12.3±1.0)and(18.0±2.0)mSv,respectively.The CTDIvol and ED values for 2C_2 group were about 32% lower than those of NC_2 group and were statistically significant with P0.01.Conclusion The adaptive post-processing filter C_2 can reduce tube current requirement by 30% for cardiac CT imaging without compromising the image quality and can reduce X-ray dosage for the examination.