Karl iterative reconstruction technique for dose reduction in chest examination using 16-slice CT:aphantom and patient study

Objective:To assess the value of Karl iterative reconstruction technique(IRT)for dose reduction in chest examination using 16-slice CT.Methods:A CT water phantom was scanned using a 16-slice CT scanner,120 kV and different tube current(150,136,123,109,95,83,68,55 and 41mAs).Except the imaging data using 150 mAs were reconstructed with filtered back projection(FBP)method,the other imaging data were reconstructed with Karl IRT.Image noise and contrastto-noise ratio(CNR)of all images with different parameters were measured and compared.In the clinical study,100 physical examinees were randomly selected into two groups(normal-dose group and low-dose group)and underwent chest CT scanning with two different protocols:for normal-dose group(group A),standard dose(120kV,150mAs)and FBP technique were used;for low-dose group,120 kV and 83 mAs were used and the imaging data were reconstructed by Karl IRT(group B)or FBP(group C).The image noise,signal-to-noise ratio(SNR),CNR,subjective score of image quality,volume CT dose index(CTDIvol)and effective dose(ED)in the three groups were measured and compared.Results:In the phantom study,the images obtained with 95 or 83mAs(60% or 50% standard dose)and Karl IRT showed comparable image noise and CNR with the images using standard dose and FBP method(P0.05).In the clinical study,the ED [(2.38±0.26)mSv]in group B and C was 51.1%lower than that[(4.87±0.37)mSv]in group A.There were no significant differences of the image noise,SNR,CNR and subjective score of image quality between group A and B(P0.05),but the SNR,CNR and subjective score of image quality of Group B were higher than those of group C with significantly statistic difference(P0.05).Conclusion:In chest CT scan,Karl IRT could maintain or improve image quality while saving 51.1%radiation dose,and is superior to FBP.