The Quantitative Evaluation Of Acute Ischemic-reperfused Myocardial Infarction In A Swine Model By Spectral CT

Part Ⅰ Cardiac Spectral CT:attenuation density, iodine quantification and spectral curve of acute myocardial infarction in swinesBackground and Objective:As a new experiment introduced in recent year, spectral CT had much potential use compared with conventional CT in the research and evaluation of cardiovascular disease. The current study was to quantitatively assess acute ischemic-reperfused MI in swine model by cardiac spectral CT. Methods:12swines underwent left anterior descending coronary artery (LAD) occlusion just distal to the first diagonal branch by balloon angioplasty.90minutes later, the balloon was withdrawn to undergo myocardial reperfusion. Cardiac spectral CT coronary angiogram (CTCA) was performed after4±1days of successful acute MI model establishment. The signal to noise (SNR), contrast to noise ratio (CNR) and noise were compared among the21monochromatic energy images from40keV to140keV at an interval of5keV. The optimal energy image for MI delineation was chosen base on it. The characteristics of MI on optimal keV, high voltage and iodine density images were evaluated. The differences of CT value, iodine concentration (IC), and spectral curve among MI, risk area and remote myocardium were investigated by analysis of variance (ANOVA) or t test.1,3,5,10, and15minutes after contrast material administration, the delayed enhancement images were acquired to observe the evolution of MI on optimal keV images of spectral CT. The best delay time for MI evaluation was determined consequently. Addtionally, cardiac magnetic resonance imaging was performed to help determine the area at risk (high signal on T2images) in the current study. After radiologic examination, overdose muscle relaxant was given to swine. The heart was excised and sliced in4mm short axis. Each slice was stained by TTC to delineate the location and extent of MI. Results:From40keV-140keV, the70keV-75keV images were defined the optimal keV images for MI evaluation due to higher SNR, CNR, and lower noise. Significant differences of CT value, IC on spectral CTCA were found among infarction, risk area and remote myocardium on optimal keV (70keV), high voltage and iodine density images (p<0.05), especially on70keV images with higher SNR, CNR and lower noise (p<0.01). The start values and the log transformed slopes of infarct myocardium, risk area and remote myocardium had significant differences. The infarction enhancement was best shown in images obtain5～10minutes after contrast material administration on70keV images, the contrast between infarction and adjacent myocardium was more prominent. Conclusion:The spectral CTCA could assess acute myocardial infarction by CT value measurement.70keV images with higher SNR, CNR and lower noise was preferable. In addition, the IC and spectral curve also help the infarction evaluation.5～10minutes after contrast material administration was regard as the best delay time to demonstrate MI in swine. Part II Acute ischemic-reperfused MI:the comparison between spectral CTCA and myocardial perfusion SPECT as well as TTC stainBackground and Objective:The current study was to investigate the ability of spectral CTCA to evaluate MI and myocardial perfusion in swine model by comparing the cardiac spectral CTCA with TTC stain qualitatively and with myocardial perfusion SPECT quantitatively in MI recognition. Methods:12acute MI model of swines (weight,20.23±1.23kg,5male,6.0±0.7months) were established. LAD just distal to the first diagonal branch was occluded by balloon angioplasty.90minutes later, the balloon was drawn back to undergo myocardial reperfusion. Spectral CTCA, myocardial perfusion SPECT were performed after4±1days of successful acute MI model establishment. The images of spectral CTCA and TTC stain identify MI segments by their own criteria. Myocardial segmentation was according to American Heart Association standard. Cohen κ test was used to analysis the consistency between spectral CTCA and TTC stain in MI segment differentiation. In addition, receiver operating characteristic (ROC) curve was used to investigate the ability of spectral CTCA to differentiate MI segments confirmed by TTC stain. The myocardial defect of17segments measured by spectral CTCA and myocardial perfusion SPECT underwent Pearson correlation and intraclass correlation coefficient (ICC) consistency analysis. Accordingly, the ability of spectral CTCA to evaluate myocardial perfusion had been investigated. Results:12swines underwent acute MI model establishment successfully.2of them died of ventricular fibrillation after PCI.1of them died of ventricular fibrillation during the spectral CTCA examination. The rest9swines (5.3±0.6months,20.17±1.35kg,3male) all underwent spectral CTCA and myocardial perfusion SPECT examination.53and58myocardial segments were identified as MI by spectral CTCA and TTC stain respectively according to their diagnostic criteria. Cohen κ test demonstrate moderate consistency between spectral CTCA and myocardial perfusion SPECT in MI segment differentiation (κ=0.681, p<0.001). ROC curve showed high diagnostic accuracy of spectral CTCA to differentiate myocardial infarct segments (sensitivity,0.810; specificity,0.937; positive predictive value,0.887; negative predictive value,0.880and accuracy,0.874, p<0.001). Spectral CTCA identified53segments which myocardial perfusion defect larger than30%.47of the53segments were confirmed as MI segment by TTC stain. The mean perfusion defect of153segments in9swines was21.27%. The myocardial perfusion SPECT identified51segments which myocardial perfusion defect larger than30%.44of the51segments were confirmed as MI segment by TTC stain. The mean perfusion defect of153segments in9swines was19.82%, with no significant statistically difference with spectral CTCA (p=0.06). The correlation between spectral CTCA and myocardial perfusion SPECT was high in myocardial perfusion assessment. Conclusion:The spectral CTCA could identify MI segment confirmed by TTC stain with high diagnostic ability. In other words, spectral CTCA could assess acute MI qualitatively; however, the small MI may be missed by spectral CTCA examination. In addition, significant correlation and good consistency were investigated between70keV images of spectral CTCA and myocardial perfusion SPECT in myocardial perfusion defect measurement. Part Ⅲ Evaluation of myocardial infarction by iodine quantification and TUNEL stainBackground and Objective:The spectral CT could be used to evaluate myocardial perfusion by iodine quantification on the basic material decomposition image noninvasively. The purpose of this study was to evaluate IC of the no-reflow region, infarction and remote myocardium of acute ischemic-reperfused MI model in swines by spectral CT. Its correlation between iodine quantification and tunnel stain was analyzed. Methods:In compliance with the institutional animal care and use committee, Chinese mini swines received human care.12swines (5male,6.0±0.7months old, weight,20.23±1.23kg) underwent Percutaneous Coronary Intervention (PCI) to produce acute reperfusion MI by balloon dilation.4±1days after acute ischemic-reperfused MI model establishment, cardiac spectral CTCA and late enhancement imaging at5minutes after contrast material injection were performed to evaluate MI. The objects with no-reflow phenomenon on late enhancement imaging were chosen. The IC in no-reflow region, infarction and remote myocardium was measured. After radiologic examination, overdose vecuronium bromide was given in venous, the heart were excised and sliced into4mm short axis slices. With the consideration of spectral CT images and gross specimen, serial cutting sections in the no-reflow region, infarction and remote myocardium were used for immunofluorescent staining. Cell apoptosis was detected by a terminal deoxynucleotidyl transferase-mediated dUTP Nick-End Labeling (TUNEL) stain by using the In Situ Cell Death Detection Kit Fluorescein according to the manufacturer’s instructions. A Leica TCS SP5confocal microscope were used for acquisition of immunofluorescent staining images in3random field of view. The TUNEL positive nuclei were counted on each section by Image analysis system "Image-Pro Plus Version6.0". The results were represented as positive nuclei count/area and the mean value were recorded. The differences among groups were compared by using ANOVA and least significant difference test. The correlation between IC and cell apoptosis of no-reflow region, infarction and remote myocardium was test by Pearson correlation analysis. P<0.05was considered statistically significant. Results:The iodine concentrations were1043±282ug/cm3,1867±344ug/cm3, and3507±331ug/cm3for of no-reflow region, infarction and remote myocardium respectively. There was significant among them (p<0.001). The apoptosis cells in no-reflow region, infarction and remote myocardium were (2661±231)/mm2,(2270±241)/mm2and (27±22)/mm2respectively. Significant differences were detect among them (p<0.001). There was significant inverse correlation between iodine concentration and cell apoptosis (r2=0.871, p<0.001). Conclusions:The IC calculated on spectral CT images could differentiate no-reflow region from infarction or remote myocardium. Furthermore, the myocardial IC on spectral correlated with the TUNEL stain of apoptosis cell in acute MI of swine models. The iodine quantification on cardiac spectral CT may add valuable information for risk stratification in the future.