Effect Of Reconstruction Algorithms On Coronary Artery Calcium Score Using Reduced Radiation Dose Protocols And Study Of Myocardial Function In Coronary Chronic Total Occlusion

Part OneEffect of Different Reconstruction Algorithms on Coronary Artery Calcium Score Using Reduced Radiation Dose ProtocolBackground and Objectives:Coronary artery calcium(CAC)scoring is a reliable,reproducible,noninvasive imaging technique used to assess the asymptomatic patients with intermediate cardiac risk.It is also a good predictor of future cardiovascular risk independent of conventional risk scores,such as the Framingham risk score.Agatston score(AS)method,which has been introduced for the first time in 1990C,is the main system for quantification of CAC,however,the high image noise and radiation dose of AS with reference protocol limited the use for asymptomatic people.Thus,the purpose of our study is to evaluate the effects of different iterative reconstruction(IR)algorithms on coronary artery calcium(CAC)score quantification using reduced radiation dose(RRD)protocol in an anthropomorphic phantom and patients.Materials and Methods:A thorax phantom was scanned with the reference(120 kv,80 mAs)and RRD protocols(120 kV,20 mAs-80 mAs,5 mAs interval)using a 256-slice CT scanner.Raw data were reconstructed with FBP and other IR algorithms(iDose4-level-1-7 and IMR-level-1-3).Agatston score(AS)were calculated and the correction factor was derived from linear regressions analysis between reference and other image series.Forty patients were scanned with RRD protocol(50 mAs)and reconstructed with FBP,iDose4-level-4 and IMR-level-2.AS was calculated and was corrected by applying a correction factor for the IMR group.Agreement of risk stratification with different reconstruction algorithms was also analyzed.Results:For the phantom study,the tube current of 50 mAs was determined for clinical study and the correction factor was 1.14.For the clinical study,AS from iDose4 and IMR groups were both significantly lower compared to the FBP group.After applying the correction factor,the adjusted AS from the IMR group had no significant difference with the FBP group.The agreement in risk stratification between FBP and IMR was improved from 0.81 to 0.85.Conclusions:A correction factor of 1.14 should be applied for the clinical RRD CAC scoring scan reconstructed with IMR to reduce the AS under-estimation effect and maintain excellent agreement for patient risk stratification with images reconstructed with FBP.Part TwoEvaluation of Coronary Chronic Total Occlusion Patients Using Dynamic CT Myocardial Perfusion ImagingBackground and Objectives:Coronary chronic total occlusions(CTO)are the most serious lesions in coronary artery disease(CAD).Successful percutaneous coronary intervention(PCI)can improve the prognosis and quality of life of CTO patients.Effective evaluation of CTO myocardial perfusion function and survival myocardium before PCI can help cardiologists evaluate the benefit of PCI and prognosis of CTO patients more objectively.Coronary collaterals circulation(CCC)are intraarterial connections that provide blood flow to a vascular territory whose original supply vessel is obstructed,which could improve myocardial perfusion function and protect survival myocardium in CTO patients.The classical and widely used angiographic grading system of CCC was described by Rentrop,which cannot evaluate function of CCC in maintaining myocardial perfusion accurately.Dynamic CT myocardial perfusion imaging(CT-MPI)could evaluate the changes of myocardial hemodynamic quantitatively,thus can assess myocardial perfusion function and survival myocardium more accurately.The purpose of this study were(1)to evaluate diagnostic performance of CT-MPI on myocardial perfusion function of CTO patients and(2)to evaluate diagnostic performance of CT-MPI and ECV based dual-energy CT(DECT)on CCC of CTO patients.Materials and Methods:The institutional review board of our institution approved this study and all patients signed written informed consent.21 CTO patients who were diagnosed by coronary angiography(CAG)and performed single-photon emission computed tomography myocardial perfusion imaging(SPECT-MPI)were included in this study.All of patients were scanned with specialized CT-MPI protocol in third generation dual-source CT and the dual-energy CT scan was run after a 7-min delay.Myocardial blood flow(MBF),myocardial blood volume(MBV),time to start(TTS),time to peak(TTP),extravascular extracellular volume(EEV),flow extraction product(FE)and perfusion capillary blood volume(PCBV)were recorded by drawn region of interesting(ROI)on every myocardial segment.Ratio of myocardial blood:flow(rMBF)and extracellular volume(ECV)based dual-energy CT(DECT)were calculated.Patients were divided into normal perfusion and abnormal perfusion groups,different ischemic degrees groups,myocardial survival and infarction groups based on SPECT-MPI.Quantitative parameters of different groups were compared and ROC analysis were performed.Patients were divided into well-developed collaterals and poorly-developed collaterals groups based on Rentrop grade.Quantitative parameters of different groups were compared and Spearman analysis were performed between significant parameters and Rentrop grade.Normality of the data were assessed Kolmogorov-Smirnov test.For the variables with normal distribution,difference of parameters between two groups were compared by independent-sample t test,difference of parameters among multiple groups were compared by ANOVA and further multiple comparison of intra-group were used LSD-t test.For the variables without normal distribution,difference of parameters between two groups were compared by Mann-Whitney U rank sum test.A P value of 0.05 was considered significant.Results:1.21 CTO patients with 357 myocardial segments were included in this study,there were 16 men and 5 women and average age was 60.71 years2.There were 235 myocardial segments in normal perfusion group and 122 myocardial segments in abnormal perfusion group respectively.MBF?rMBF?MBV?FE?PCBV and EEV in abnormal perfusion group were lower but TTS and TTP were higher compared to normal perfusion group(all P<0.05).The AUC of MBF were 0.809,which were higher than other parameters.The cutoff value of MBF was 74.5 ml/100ml/min,Sensitivity and specificity were 0.78 and 0.73 respectively.3.MBF and rMBF were decreased as ischemic level increasing but moderate and severer ischemic group have no significant deference(P=0.722 and 0.709 respectively).The AUC of MBF and rMBF were 0.836 and 0.872 respectively.The cutoff values were 67.5 ml/100ml/min and 78.13%respectively when distinguishing myocardial survival and infarction.Sensitivity were both 0.83 and specificity were 0.74 and 0.79 respectively.4.MBF,MBV,FE and EEV in well-developed collaterals group were significantly higher than that in poorly-developed collaterals group(all P<0.05),but there was no significant difference with other parameters(all P>0.05).However,there were poor relativity between MBF,MBV,FE,EEV and Rentrop grade(all |r|<0.3);5.The ECV based on DECT have no significant difference between well-developed collaterals and poorly-developed collaterals groups(P=0.906).Conclusions:1.Quantitative parameters of CT-MPI have good diagnostic value for myocardial perfusion,ischemic levels and collaterals circulation in CTO patients;2.there seems no correlation between quantitative parameters of CT-MPI and Rentrop grade;3.ECV based on DECT do not predict CCC in CTO patient accurately.