The Application Value Of IQon Spectral CT In The Diagnosis Of Pulmonary Embolism

Part One: Optimal Window Setting for 40 kev Virtual Monoenergetic Images Derived from IQon Spectral CT Pulmonary AngiographyObjective To explore the image quality of 40 keV virtual monoenergetic images（VMI）derived from IQon spectral CT Pulmonary Angiography and its optimal window setting.Methods From January 2021 to December 2021,37 patients with pulmonary embolism who underwent IQon spectral CT Pulmonary Angiography were retrospectively enrolled.PI and VMI_40keV were generated using iterative reconstruction and spectral reconstruction techniques after scanning.The CT attenuation of the pulmonary artery,image noise and contrast noise ratio（CNR）were compared between PI and VMI_40keV.Window-individual settings of PI and VMI_40keV were adjusted and recorded(Ind.-PI/VMI_40keV).Window-calculated settings(Calc.-PI/VMI_40keV)were mathematically calculated via regression analysis and Optimized window settings(Opt.-PI/VMI_40keV)were obtained.Image quality was assessed with a 4-point scale,and the diameter of the upper left anterior pulmonary artery in PI and VMI_40keV were measured with different window settings.Results The CT attenuation of the pulmonary artery [（906.22±105.82）HU] and CNR [（73.34±13.89）HU] in VMI_40keV were higher than those in PI [（344.15±72.06）HU,（21.89±5.27）HU],the difference were statistically significant（t=37.20,t=22.37,P<0.001）;Image noise [（11.83±2.23）HU] was less than in PI [（13.35±0.97）HU],the difference was statistically significant（t=5.11,P<0.001）.The Opt.-PI/VMI_40keV are 870HU/230 HU and 1510HU/490 HU respectively.Compared with the window-standard setting（Std.-）,all adjusted window settings had higher image quality scores,and the differences between Std.-and Ind.-in PI or VMI_40keV were statistically significant（all P < 0.001）,while there were no statistically significant differences between Ind.-and Calc.-,Calc.-and Opt.-（all P>0.05）;And the window-standard setting of VMI_40keV overestimated pulmonary artery diameter（12.63±2.78 vs 9.22±0.74）.Conclusions VMI_40keV derived from IQon spectral CTPA have higher image quality than PI.It is recommended to adjust window settings(PI:870,230 HU,VMI_40keV:1510,490HU)to obtain the best image quality of pulmonary embolism.Part Two: The Value of IQon Spectral CT Pulmonary Angiography in Qualitative Diagnosis and Quantitative Evaluation of Pulmonary EmbolismObjective To explore the value of IQon spectral CT Pulmonary Angiography in qualitative diagnosis of PE and quantitative assessment of pulmonary parenchyma perfusion.Methods From January 2021 to December 2021,37 patients with pulmonary embolism who underwent IQon spectral CT Pulmonary Angiography were retrospectively enrolled.On the spectral CT offline workstation ISP,the conventional CTPA,VMI_40keV,IDI and Z-eff fusion map and EDI were reconstructed using the SBI.The number and location of emboli in segmental pulmonary arteries,subsegmental pulmonary arteries and below were analyzed and recorded.Conventional CT attenuation,iodine density value,effective atomic number value and electron density were measured in the lung perfusion defect area and the normal lung parenchyma area at the same position on the opposite side by ROI.Statistical comparisons were performed using paired-sample Wilcoxon rank-sum test,and the ROC curves were used to evaluate the diagnostic performance of quantitative indicators in differentiating PE perfusion defect area and normal lung parenchyma area.The differences in AUC among the quantitative indicators were compared by the De Long test.Results A total of 40 intraluminal thrombi were detected in 37 patients,of which 27 were located in segmental pulmonary arteries and 13 were located in subsegmental pulmonary arteries and below.Conventional CTPA initially found only 37 emboli,and special spectral CT images found additionally 1 pulmonary segmental artery embolus and 2 subsegmental arterial emboli,increasing the detection rate of PE by 8%.The conventional CT attenuation in the perfusion defect area was higher than that in the normal lung parenchyma area,and the difference was statistically significant（Z=-3.347,P=0.001）;the iodine density value and effective atomic number value were lower,and the differences had statistical difference（Z=-5.511,Z=-5.511,both P<0.001）.However,the electron density was slightly lower in the perfusion defect area（19.85% EDW vs 21.25% EDW）,and the difference was not statistically significant（Z=-0.612,P=0.541）.ROC curve showed that,the sensitivity of iodine density value and effective atomic number value were 95.0% and 97.5%,the specificity of the both were 100.0%,and the AUC were 0.998 and 0.999,respectively.The sensitivity and specificity of the conventional CT attention were 42.5% and 87.5%,and the AUC was 0.654.The De Long test showed that,the AUC difference between iodine density value or effective atomic number value and conventional CT attention had all statistical difference（both P <0.001）;while the AUC difference between iodine density value and effective atomic number value had no statistical difference（P =0.480）.Conclusions IQon spectral CT can improve detection of PE in the arteries of the lung segment and below and generate material-decomposed images for quantitative assessment of pulmonary flow and perfusion defects.IDI and Z-eff as predictors for distinguishing perfusion defects from normal lung parenchyma.