Dose reduction potential in abdominal CT with advanced iterative reconstruction algorithms: A phantom study

Objective To assess the dose reduction potential in abdominal CT of advanced reconstruction algorithms(model-based iterative reconstruction and adaptive statistical iterative reconstruction ) with a standard man phantom by comparing image noise and contrast-noise-ratio(CNR) with the filtered back projection(FBP) reconstructions.Methods A Fluke Biomedical RANDO standard man phantom was scanned with Discovery CT750 HD under different tube currents(400 mA,350 mA,300 mA,250 mA,200 mA,180 mA,160 mA,140 mA,120 mA,100 mA,80 mA,60 mA,50 mA,40 mA,30 mA,20 mA and 10 mA),and the other parameters were: Tube voltage was 120 kV,scanning time was 0.60 s,screw pitch was 0.984,slice thickness was 5 mm,interlamellar spacing was 5 mm,matrix was 512×512,and DFOV was 35 cm.Volume CT dose indexes(CTDIvol) and dose-length product(DLP) were recorded.Three sets of 0.625 mm slice thickness CT images were reconstructed with FBP,50%ASiR and MBIR.CT value,imaging noise and contrast-to-noise ratio(CNR) for the lumbar vertebra relative to muscle were measured.Three experienced radiologists assessed all the 3 set of images blindly and subjectively.Results Under different tube currents(400—10 mA),compared with FBP,the average image noise reduction with 50%ASiR and MBIR was(27.86%—31.46%) and(45.36%—86.37%),respectively,and the CNR increase for lumbar vertebra with 50%ASiR and MBIR was(28.68%—31.08%) and(46.43%—84.38%),respectively.The minimum tube current for displaying lumbar vertebra clearly was 200 mA(FBP),140 mA(50%ASiR) and 80 mA(MBIR),respectively.On the other hand,to get similar quality images,MBIR and 50%ASiR could reduce dose by 59.91% and 35.94% compared with FBP,respectively.Conclusion Advanced reconstruction algorithms can greatly reduce image noise and improve image CNR.Compared with FBP,it is possible to reduce dose by 60% in abdominal CT examination with MBIR reconstruction.