RESUMO
Objective:To investigate the feasibility of reducing the radiation dose on coronary artery calcium score (CS) of virtual non-contrast (VNC) scanning in dual-layer spectral coronary CT angiography(CCTA).Methods:One hundred and twenty-two patients were examined on a dual-layer spectral detector CT scanner from March 2019 to August 2020. Volume CT dose index (CTDI vol), dose length product (DLP), effective dose ( E) were all evaluated for each patient. CS was calculated from both true non-contrast (TNC) and VNC images for left anterior descending (LAD), left circumflex (LCx), right coronary artery (RCA), and the total coronary artery (Total) by two radiologists independently. Pearson′s correlation coefficient was calculated for measuring the association between variables. The correction coefficients of each branch (λ LAD, λ LCx, and λ RCA) and the average correction coefficient (λ AVG) of the total coronary artery were obtained. The calibrated calcium score (CCS_VNC) was equal to λ multiplied by CS_VNC. The CS_TNC and CCS_VNC were compared using repeated oneway analysis of variance test. Correlation analyses for CS_TNC and CCS_VNC and agreement evaluation with Bland-Altman-Plots were performed. Results:The average effective doses in TNC, CCTA and total group were 0.69, 6.47 and 7.16 mSv, respectively. The effective dose was reduced by 10.6% and the scan time was reduced by 39% while using VNC images. There were significant differences among the CS_TNC and CS_VNC of LAD, LCx, RCA and Total ( t=6.75, 5.33, 4.99, 6.60, P< 0.05). Excellent correlations were observed between CS_VNC and CS_TNC ( R2 values were 0.929, 0.896, 0.958, and 0.918; λ values were 2.18, 1.18, 2.15, and 2.07, respectively). There were no significant statistically difference among the CS_TNC, CCS_VNC AVG, and CCS_VNC LAD/RCA of the LAD and RCA (all P> 0.05). The difference was statistically significant among the CS_TNC, CCS_VNC AVG, and CCS_VNC LCx of the LCx ( F=10.94, P<0.05). The paired comparison were performed in groups and the differences were statistically significant between the CS_TNC versus CCS_VNC AVGand CCS_VNC AVG versus CCS_VNC LCx ( t=3.31, 3.43, all P<0.05). There was no significant statistically difference between the CCS_VNC LCx and CCS_VNC AVG( P>0.05). Conclusions:It was feasible to accurately evaluate the CS_VNC from spectral data in comparison to TNC imaging, and to reduce the patient radiation dose and acquisition time.
RESUMO
Objective To assess the advantages of multi-source RF transmission(MT) for balanced fast field echo(BFFE) cardiac cine imaging.Methods Fifteen volunteers were scanned on a clinical 3.0 T MR system equipped with MT.Acquisition of B1 maps with and without MT were followed by axial and four chambers BFFE cine imaging for all subjects with different transmission modes[single source RF transmission (ST),MT and MT with allowable shortest TR(MTS)].The B1 field uniformity and contrast to noise ratio (CNR) were quantitatively analyzed.The B1 field uniformity was evaluated by the pixel values within the ROI and was compared with Student t test.CNR was defined as follows:(SIblood-SImyocardium)/ 0.5 ×(SDblood + SDmyocardium).CNR were tested with one-way ANOVA for three groups comparision and with LSD for inter-group comparison.Image qualities were blindly assessed by 2 readers with a 4-score scale.Global image quality scores were tested for statistical significance by using the nonparametric paired sample Friedman rank test for three groups and the Wilcoxon signed rank test for further inter-group comparison.The Kappa statistics was used to assess interreader agreement.Results B1 homogeneity was significantly improved for images with MT compared with ST under the condition of other parameters unchanged (t =21.632,P ＜0.01).In left ventricular,CNR of blood and myocardium was improved from 10.8 ±2.2 for ST to 14.4 ± 2.4 for MT and 14.1 ± 2.2 for MTS.In fight ventricular,it was improved from 7.7 ± 1.2 for ST to 12.2 ± 1.4 for MT and 12.0 ± 1.2 for MTS.The differences were statistically significant (F =11.617,61.472,P ＜0.01).The images of MT and MTS groups demonstrated greater CNR versus the ST images.There was no statistical difference between latter two groups.The image scores of Reader 1 and 2 were 4.60 ± 1.18 and 4.73 ± 1.10 for ST,6.53 ± 1.19 and 6.67 ± 1.29 for MT and 6.73 ± 1.03 and 6.73 ± 0.88 for MTS respectively.There were statistically differences among three groups (x2 =23.577,24.275,P ＜ 0.01).The image quality was improved on BFFE images using MT and MTS technology compared to ST technology,and there were also significant differences.The interreader agreement between two readers was good [K=0.643,0.722 and 0.814(P ＜0.05) for ST,MT,and MTS group respectively].Conclusions MT technology significantly improves B1 field uniformity,increases CNR and reduces artifact on BFFE cardiac cine images.The TR is decreased within the normal SAR ranges,and thus scanning speed is increased.