The Influence Of Different Monochromatic Spectral Images To Imaging Quality And Transluminal Attenuation Gradient In Spectral CT Coronary Angiography

Part Ⅰ Imaging quality optimization of CT coronary angiography by using virtual monochromatic spectral imagesBackground and Objective: CT coronary angiography has been widely used as an effective noninvasive imaging modality in the diagnosis of coronary heart disease. With the development of multiple slices helical CT, spectral CT have become another development direction of CT technology research. As the birth of the spectral CT, spectral CT had much potential use compared with conventional CT in the research and evaluation of cardiovascular disease. The aim of the current study was to evaluate objective imaging quality indices to determine the optimal monochromatic spectral image levels of CT coronary angiography. Methods and Materials: 100 patients(59 males, mean age 60.0±2.7 years old) underwent CT coronary angiography examination on a single-source dual-energy spectral CT scanner. The patients were divided into the normal group(no coronary artery plaque) and the lesion group(with coronary artery in any of the three main arteries). All the spectral imaging data were reconstruct to monochromatic spectral images from 40 to 140 ke V in 10 ke V increments with 30% ASi R. For 11 groups of monochromatic spectral image, the imaging Noise, SNR, CNR of all coronary arteries(proximal, middle, and distal segments of LAD, LCX, and RCA) in both groups were calculated and compared by using One-Way ANOVA and independent sample t test. In addition, the CNR of coronary plaque was calculated in 242 coronary artery segments of lesion group. P<0.05 was considered as the statistically significant. Results: The general trend from the ANOVA and Tukey pair comparison among groups showed that the cutting-off value for monochromatic spectral image Noise was 60 ke V. The image CNR and SNR of the range from 40 to 70 ke V monochromatic spectral image were significant higher than the other ke V intervals. There were no difference of SNR and CNR among normal and lesion group in 60 ke V level. Conclusion: monochromatic spectral images from 60 to 70 ke V levels could significantly improve the coronary image quality by raising the CNR and reducing the Noise in both normal and lesion group. Considering the overall objective imaging quality indices, monochromatic spectral image from 60 to 70 ke V levels could be used as the optimal ke V settings for the coronary arteries assessment.Part Ⅱ The influence of different ke V levels to transluminal attenuation gradient(TAG) in CT coronary angiography by using virtual monochromatic spectral imagesBackground and Objective: The conventional CT coronary angiography only can provide anatomic information of coronary artery, therefore, people try to use various methods to realize the one-stop examination of the heart to get the anatomic and functional information of coronary artery. Transluminal attenuation gradient was defined as the linear regression coefficient between luminal attenuation and axial distance. Some scholars consider that the TAG can be used to evaluate hemodynamic significance of coronary artery. At present, the value of TAG for evaluating the hemodynamic significance of coronary artery needs further research. The variance of TAG may caused by acquisition parameters, contrast density, and individual difference. The study was aimed to study the TAG changes in deferent energy levels of virtual monochromatic spectral images. Methods and Materials: A total of 50 patients(27 males, mean age 58±2.7 years old) with no stenosis in any coronary artery underwent coronary CTA examination on a single-source dual-energy spectral CT scanner(Discovery CT750 HDCT FREEdom Edition scanner, GE Healthcare, Milwaukee, WI, USA). All the spectral imaging data were reconstruct to monochromatic spectral images from 40 to 140 ke V in 5 ke V intervals on AW 4.6 work station. TAGs of the three main branches(LAD、LCX and RCA) were calculated at each ke V data set. The TAG changes among the branches and ke V levels were compared by using ANOVA. P<0.05 was considered as the statistically significant. Results: The whole trend of change of TAG of LAD、LCX and RCA from 40 to 140 ke V are indentical. From 40 to 70 ke V, TAG increases significantly; from 70 to 100 ke V, TAG increases more gentle; from 100 to 140 ke V level, increase is very gentle and tend to be a straight line. One-way ANOVA showed that three vessels of TAG values were significantly differences from 40 to140 ke V. In the 70 ke V, the TAG value of RCA and left coronary artery system are significantly different, the TAG value of RCA is slightly smaller than left coronary artery. Conclusion: TAG differed from left to right coronary arteries. At different ke V levels, the value of TAG is different. The energy level was an important factor to affect the TAG values.