Effects Of Stent Types On The Coronary Angiography With 64-MSCT And Optimization Of Reconstruction Kernel

BackgroundWith the aging of the population,the morbidity of coronary artery disease(CAD) increased rapidly.According to the MONICA(Comparison of the Trends of Incidence Rate and Mortality Rate of Acute Coronary Events between Urban and Rural Area in Beijing)schedule of china in 1984～1993,annual incremental rate of acute CAD event morbidity was 2.3%.Coronary artery stenting is currently the predominant management of nonsurgical myocardial revascularization because of its less invasive and effective properties.But loss of the normal lumens after stenting lead to thrombosis and excessive proliferation of neogenesis endomembrane which resulted in in-stent restenosis(ISR).So the most important sequel of coronary artery stenting is ISR.Although coronary arteriography(CAG) was still the gold standard method on the diagnosis of ISR,it had many drawbacks such as high cost,invasive,serious complications by chance and repeated examinations which could induce to patient rejection.Besides,only a small fraction of patients(about 53%) should receive advanced interventional therapy.So it was imperative to find a reliable and non-invasive method to detect and evaluate coronary artery diseases before interventional therapy. According to published literatures,electron beam computed tomography, magnetic resonance imaging and 4- or 16-slice computed tomography faced a major problem on detection of ISR in most patients due to volume artifacts from the highly attenuated stent struts.With the increase of time resolution and spatial resolution and numerous post-processing reconstruction techniques of 64-multislice CT(64-MSCT), the quality of coronary stents CT arteriongraphy(CTA) was greatly improved.But metal artifacts were still the most important influential factor in coronary stents CTA.Some researchers stated that the artifacts of coronary CTA caused by stents were stent-type-dependent,which resulted in variable diagnosis accuracy.Physicians paid more attention on artifacts dependented on stent types.Which type of the stent may lead to overestimate or underestimate of ISR?Sixty-four-MSCT offers multiple post-processing reconstruction techniques, including different reconstruction kernel,Is the conventional kernel still suitable for coronary artery stent CTA? What is the outcome,when using different reconstruction kernel.Which one is the best suitable for coronary artery stent CTA? In order to solve the above issues,we made a series of researches.PurposePart oneTo analyze effects of stent types on the coronary angiography with 64-MSCT, including the material,inner diameter and struts of stents.Part twoTo optimize the reconstruction kernel of coronal artery stent CTA with 64-MSCT.Material and Methods Part oneCoronary artery CTA images of 60 patients with coronary artery implanted stents and suspected ISR were retrospectively analyzed.All of the patients received CAG detection after CT examinatoin within 3 months.The time,site,number,and character of the implanted stent were recorded,including the material,inner diameter and struts of stent.Sixty patients with a total of 95 stents were grouped into:(1) cobalt-chromium alloy group and stainless steel group based no stent material,(2) group of inner diameter≥3.5mm and＜3.5mm groups based on stent inner diameter, and(3) group of strut≤0.1mm and＞0.1 mm group based on stent struts.The accuracy, sensitivity,specificity,positive predictive,negative predictive and Kappa value for CTA diagnosis of prominent ISR were calculated.And we intended to investigate the influence of stent types on the CTA.and the diagnostic accuracy of CTA in detecting prominent ISR.The CT value of aortic root and inner stent were measured on the images which met the evaluation criteria,and the subtraction of CT value of inner stent from that of aortic root was calculated,which was defined as D.And we intended to investigate the relation between stent types and D,between ISR and D.Part twoTwenty-three patients with coronary artery implanted stent and suspected ISR underwent CT examination.The images of conventional coronary CT examination were reconstructed with different kernel,including soft,standard,lung,detail and the bone kernel with a slice of 0.625 mm.Image noise was measured in differernt kernel using a region of interest(ROI) technique.And the grades of stent struts artifacts and low-attenuation artifacts in stents were evaluated.The difference of image noise and artifacts when using differernt reconstruction kernel were analyzed. Statistical analysisThe statistical analysis were performed with the statistcal software packgae SPSS for Widow,version 13.0.Part one1.The accuracy,sensitivity,specificity,positive predictive,negative predictive and Kappa value for CTA diagnosis of prominent ISR(needing positive operation intervention) were calculated.2.Wilcoxon signed-rank test was applied for ranked data,comparison between artifacts of two different groups.3.Chi-square test was applied for numeration data,comparison between rate of CTA and CAG.4.Because the variable D is measurement data,the test of frequency distribution is needed.According to the frequency distribution,T-test or Wilcoxon signed-rank test was used.Part two1.Image noise is measurement data,the test of frequency distribution is also needed. According to the frequency distribution,ANOVA or Wilcoxon signed-rank test was chosen.If the data show skewness distribution,Bonferroni test was applied for comparison among(P=0.05/10=0.005).And if it was Gaussian distribution, LSD-t was used.2.Friedman's M test was used for comparison between arcifacts of different kernel. Bonferroni test was used for comparison among(P=0.05/10=0.005).ResultsPart oneNinety-five stents,including 13 types of stents,were implanted in 60 patients. Seventy-eight stems images met the evaluation criteria.The accuracy,sensitivity, specificity,positive predictive,negative predictive and Kappa value for CTA diagnosis of prominent ISR were 74.3%,81.4%,76.5%,79.5%and 0.558 respectively.Comparing to stainless steel stents,cobalt-chromium alloy stents seens less artifacts,and the rate of available evaluation(86.7%vs 77.5%,P=0.002) and the accuracy of diagnosis(94.7%vs 71.2%,P=0.034) were bigger.Stents of inner diameter≥3.5mm lead to better stent images(Rate of available evaluation:100%vs 67.9%,P＜0.001;Accuracy of diagnosis:88.4%vs 62.9%,P=0.008).The value D did not related to IRS but stent types.Part two1.Twenty-three patients with 30 stents imaging met the evaluation criteria.With the increase of kernel,the image noise ascends simultaneously(the median of image noise for soft,standard,detail,bone and lung kernel were 24.1Hu,30Hu,34.7Hu, 95.5Hu and 113.6Hu respectively,P＜0.001).the image noise of lung and bone kernel were the biggest(median:113.6Hu vs 95.5Hu,P=0.012＞0.005,lung or bone was different from other kernels,all the P valus＜0.005).The image noise of soft kernel was the smallest(just 21.1Hu,soft was different from other kernels, all the P valus＜0.005).2.With the increase of kernel,the stent struts seemed more sharp,and low-attenuation artifact in stent seemed more obvious.The stent struts seemed most obscure in soft kernel(soft was different from other kernel,all the P valus＜0.005),and seemed sharpest in lung kernel(lung was different from other kernels,all the P valus＜0.005).But lung kernel caused stent struts thickening artifacts and the most severe low-attenuation artifacts in stents.So both soft and lung kernel were unsuitable for coronary artery stent CTA.The stent strut seemed clear and sharp in both bone and detail,there are no or slight artifact surround the stents struts(Major artifact of the former is grade 1 and the latter is grade 1-2, P=0.002).Both of the kernel show good coronary artery stent CTA imaging.But the image noise of bone is 3 times that of detail,therefore considering of image noise and artifact,detail is slightly superior to bone kernel.3.When compared with conventional kernel standard,detail kernel reconstruct clear and sharp stent strut imaging(Major artifact of the former is grade 2 and the latter is grade 1,P＜0.001).Cosidering of low-attenuation artifacts,there were no statistical difference between each other(P=0.098).And image noise of detail just increase slightly(26.8Hu vs 32.3Hu,P＜0.001).Consequently detail is better than conventional kernel standard in coronary artery stent CTA.ConclusionPart oneCoronary artery stent CTA is a reliable and non-invasive method to detect prominent ISR.As compared with stainless steel stents,cobalt-chromium alloy stents showed less artifacts,and the rate of available evaluation and the accuracy of diagnosis were more bigger.Stents with inner diameter≥3.5mm lead to better stent images.We should pay attention that the ISR may be overevaluated in stainless steel stents or stents of inner diameter＜3.5mm with more artifacts on CTA.Because of metal artifacts,the value D is useless in detecting IRS.Part twoAs compared with conventional kernel standard,detail kernel offered by GE Light Speed VCT 64-slice CT showed good stent strut imaging.The stent strut seemed clear and sharp in detail kernel,and low-attenuation artifact was no or slight on detail kernel.We suggested detail kernel to reconstruct coronary artery stent CTA images.