| Objective:To evaluate the feasibility of adaptive statistical iterative reconstruction-V(ASIR-V)to improve image quality,polyp detection rate and reduce radiation dose in CT colonography.Materials and Methods:A series of thirty artificial polyps sized from 1mm to 15mm were established by ligation in an isolated segment of porcine colon(according to polyp diameter(D)were divided into 3 groups:ten ? 1mm and<5mm,ten? 5mm and<10mm,ten>10mm and ?15mm).Volume data was acquired on Revolution CT scanner(GE,USA)with High Definition scan at different scan methods:120 kVp with different mA(10,30,50,70,90,100,120,140,160,180,200,220,240,260,respectively).Images were reconstructed with six different ASIR-V levels of 0(filtered back projection,FBP),10%,30%,50%,70%and 90%.Two radiologists(10 and 3 years of CTC diagnosis experience),blinded to tube current and methods of image reconstruction,independently interpreted the CTC using CTC post processing images(CTVE,MPR,VD,VR)in 84 different conditions(14 kinds of tube current for the combination of 6 kinds of reconstruction algorithms).The readers assigned a subjective image quality by using a 4-point score and a confidence rating by using a 5-point score,calculated polyp detection rate of each image.While two observers measured and analyzed the objective data independently,including image noise(SD),signal-to-noise ratio(SNR)and contrast-to-noise ratio(CNR).The kappa test was used to assess interobserver agreement in subjective image quality score and per-polyp confidence level.When the two were in good agreement,the average score of two observers was used for statistical analysis.To assess the diagnostic performance of different tube current and different level of reconstructions in polyp detection,polyp detection rate and confidence rating were compared using the linear regression.ICC test was used to examine the consistency of the measurements between two observers,the average data from two observers were performed for further statistical analysis.SD,SNR,CNR was performed for statistical analysis in different tube current and different levels of ASIR-V using variance analysis(ANOVA).A P value of 0.05 or less was considered to be statistically significant.Results:Interobserver agreement for subjective image quality score was good with a kappa value of 0.683.The variation of the tube current(r=0.734,P=0.000)and ASIR-V level(r=0.220,P=0.044)is related to the subjective score of image quality.Under the condition of the same tube current,image quality score of 50%ASIR-V reconstruction was the highest.Interobserver agreement for per-polyp confidence rating was good with a kappa value of 0.831.The tube current(r=0.884,P=0.000)and the changes of ASIR-V(r=0.861,P=0.028)will affect the per-polyp confidence rating,the difference was statistically significant.At the same level of tube current,50%ASIR-V reconstruction images showed higher confidence.All the polyps were detected when the lowest scanning tube current was 30mA and the lowest ASIR-V weight was 50%.When the tube current was 50mA and above,the detection rate of any level of ASIR-V reconstruction was 100%.When the tube current was lower than or equal to 30mA,the increase of tube current(r=0.677,P=0.016)and ASIR-V(r=0.644,P=0.024)can improve the detection rate of all polyps,there was a significant correlation between them.The size of polyps was significantly correlated with the detection rate of polyps(r=0.688,P=0.000).With the increase of polyp diameter,the detection rate of polyps increased with the same condition.The tube current at the 1 ? D<5mm polyps detection was 30mA,with 50%ASIR-V reconstruction.Tube current increase can improve polyp detection rate which diameter less than 5mm,showed a significant correlation between them(r=0.729,P=0.007).When the tube current was 10mA,levels of ASIR-V reconstruction had no significant effect on the polyp detection rate(r=0.756,P=0.082),when the tube current was 30mA,ASIR-V levels increased to improve the detection rate of polyps,there was significant positive correlation between them(r=0.924,P=0.008).When the current was above 50mA,the detection rate was 100%,the difference was not statistically significant.The minimum tube current for 5<D<10mm polyps detected was 30mA,with 30%ASIR-V reconstruction,tube current can affect the detection rate of polyps,showed a significant correlation between them(r=0.612,P=0.034);when the tube current was 10mA or 30mA,there was a significant positive correlation between ASIR-V levels and polyp detection rate(P<0.05).With the increase of ASIR-V level,polyp detection rate gradually increased.For the D = 10?15 polyps,all the conditions of the polyp detection rate can reach 100%,the difference was not statistically significant.When the tube current was 30mA,the effective dose was 0.61mSv.Two objective data consistency is good.Image noise(F=423.58,P=0.000),SNRs(F=124.26,P=0.000)and CNRs(F=1030.17,P=0.000)of different tube current and different levels of ASIR-V reconstruction,the differences were statistically significant.In the same tube current,with increased levels of ASIR-V,image noise reduced,CNRs increased.SNR only in 10,120,140,160;220,240,260mA,the differences were statistically significant.For the same level of ASIR-V reconstruction,with the increase of tube current,the image noise decreased,SNR and CNR increased gradually.Conclusion:In the CT colonography,the application of ASIR-V algorithm can significantly reduce the noise and enhance the image contrast noise ratio and improve image quality,and can improve the detection rate of polyps and effectively reduce the radiation dose to ensure low dose.In the premise of ensuring low dose,ASIR-V algorithm of Revolution CT can achieve the purpose of finding and diagnosing of lesions,provide the possibility for low-dose screening. |
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