Quantification Of Individual Coronary Artery Calcified Plaques As Measured By MSCT

【Objective】To systematically assess the characteristics of individual calcifiedplaques, especially calcium concentration (CC) and the constituent ratio of eachsegment segmented by CT value, to analyze their relationship to other individualparameters and global parameters, and to approach their potential of assessing thecoronary event risk and plaque progression and regression by using 16-slice spiralcomputed tomography (16-SCT) and calibration phantom images.【Materials and Methods】Coronary artery calcium (CAC) was analyed in650 successive participants of CT coronary artery angiography examination. CAC wasdetected in 241 of 650 subjects. After excuding 55 subjects because of artifacts andabsence of phantom, we identified 186 subjects (126 men, 60 women; mean age, 61.8±10.7 years) with detectable CAC and valid images. Overall study we usedsmartscore sequence by prospectively ECG-triggered 16-SCT and the calibrationphantom for measuring bone density (GE). We determined the CC, mean CT value,Agatston score (AS), volume score (VS), calcified volume (CV), and mineral mass(MM) of each individual calcified plaque in each subject, we also determined theCV_total, AS_total, VS_total, MM_total of each subject. Additionally, we segmented eachindividual calcified plaque by CT value and obtained the constituent ratio of eachsegment, the segmental standard was 130～199HU, 200～299HU, 300～399HU and≥400HU. We performed Spearman rank correlation test to analyze the relevancebetween two variables and performed rank test to analyze differential significance. Avalue of P≤0.05 was considered to indicate statistical significance for all tests. 【Results】We identified a total of 689 calcified coronary plaques (mean, 3.70±3.81 plaques per subject; range 1 to 23) in 186 subjects, including 519 plaques in mensubjects and 170 plaques in women subjects.1. The number of individual calcified plaques was significantly more in malethan in female (P=0.004) and in high age groups (＞55 years of age) than in low agegroups (≤55 years of age) (P＜0.05).2. The distribution frequency of individual calcified plaques in coronary arterybranches is in descending turn of LAD (left anterior descengding coronary artery),RCA (right coronary artery), LCx (left circumflex coronary artery), LM (Left coronaryartery main stem), Diagonal and PDA (posterior descengding coronary artery).3. High positive correlations could be found between CC and CV, CC and VS,CC and MM. The correlation coefficients were 0.746, 0.751 and 0.826 respectively,and all of the P values are 0.000.4. CC was significantly lower in male than in female (P=0.025) and in≤55 yearsof age than in＞55 years of age (P＜0.01). The results were similar for CT value.5. The values of AS, VS, CV and MM were significantly lower in male than infemale (P＜0.01) and in≤55 years of age and 56～70 years of age than in≥70 years ofage (P＜0.005).6. The degree of heterogeneity of CC in these subjects was independent of sex(P=0.704), age (P=0.182), and number of plaques (P=0.678). The results were similarfor the degree of heterogeneity of CT value.7. The degree of heterogeneity of AS, VS, CV and MM in these subjects wereindependent of sex (P＞0.1), and except the heterogeneity of AS, the degree ofheterogeneity of other parameters were also independent of number of plaques(P＞0.05), but the heterogenerty were significantly different among age groups(P＜0.05).8. The proportion of low calcified component (130～199HU) in individualcalcified plaques was higher in male than in female, and the proportion of high calcified component (≥300HU) was higher in female than in male. With the increasingof segmental CT threshold value, the correlation relevance between the constituentratio of each segment segmented by CT value and other parameters were fromnegative to positive and more and more strong; and the constituent ratio of high CTthreshold value segment was increased with the increasing of each parameter.9. The values for AS_total, VS_total, CV_total and MM_total were not significantlydifferent between men and women (P＞0.1), but were significantly different among thethree age groups (P=0.000).【Conclusion】1. Our study of this group of cases (n=186) displayed that the number ofindividual calcified plaques, CC value, and the constituent ratio of each segmentsegmented by CT were significantly different between men and women and amongage groups. These differences may reflect the general rule of occurrence and progressof coronary artery atherosclerosis diseases, and they may be capable of interpretingsome conflicting results in previous study, and were significant for understanding therelation between CAC and coronary artery event.2. The CC of individual calcified plaques and the degree of correlations withother parameters were able to reflect the characteristics of plaques, and which may behelpful for improving the prognosis of coronary artery event risk.3. The heterogeneity of individual calcified plaques within subjects was aparameter that was independent of sex and age, which reflect the heterogeneity ofprogress of calcified plaques. The constituent ratio of each segment segmented by CTand its correlations with other parameters may be a useful method for studying theplaque stability and the progression and regression of CAC.4. The measurement and analysis of the parameters of individual calcifiedplaques, combining with other parameters, were able to provide more information forevaluating coronary artery atherosclerosis diseases.