The Experimental Study On Dual-Energy Perfusion Imaging For The Diagnosis Of Acute Pulmonary Embolism By Dual-Source CT

Pulmonary embolism(PE) is one of the most common life threatening diseases. Despite the high morbility,it is difficult to diagnose for lacking typical clinical symptoms and special examiniation,which would delay treatment and increase mortality.Imaging examinations play an important role in the diagnosis of PE. Pulmonary angiography is the gold standard for diagnosis of PE.However,due to serous trauma and a series of complications,its clinical application is limited; Magnetic resonance imaging is difficult to be used in the routine clinical practice to diagnose for acute PE patients because of a long scanning time. Scintigraphy imaging is safe,non-invasive,and high sensitive;hence,it is a valuable method of PE diagnosis.CT examination is an important method of PE diagnosis.With the great improvement of spatial and temporal resolution,CT pulmonary angiography(CTPA) can show not only main pulmonary artery,lobe and segment arteries but also subsegmental and sub-subsegmental arteries. However,CTPA has some shortcomings,such as limited sensitivity to detect peripheral or sub-subsegmental embolus of pulmonary artery,lower spatial resolution,and the disability to implement the pulmonary blood flow perfusion imaging of lung parenchyma,and so on.CT pulmonary perfusion imaging which shows the distribution of pulmonary blood flow is more sensitive to detect the perfusion defects caused by pulmonary embolus,and this is supplementary for conventional CTPA in the evaluation of distal pulmonary artery.Although conventional CT perfusion scan(dynamic scanning) can evaluate the lung perfusion,it can't cover the full lung.The technologies of the lung parenchyma densitometry and CT subtraction can access the pulmonary perfusion,but it is complex and time-consuming.So it is difficult to be used widely in the clinic.In recent years,with the advent of the dual-source CT(DSCT),dual-energy perfusion imaging(dual energy perfusion imaging,DEPI) is emerging as a new method of pulmonary perfusion imaging,which is valuable in diagnosis of PE and able to make up for the defects of CTPA.In this article,the aims of the first part are to set up the acute pulmonary embolism model,to observe dynamic changes of lung perfusion in the acute PE and with the pathology as the gold standard,to evaluate the value of dual-energy perfusion imaging to diagnose acute PE.The aim of the second part is to compare the diagnostic value of dual-energy perfusion imaging and perfusion scintigraphy imaging to diagnose acute PE with the pathology as the standard of reference. Part OneThe Experimental Acute Pulmonary Embolism in Rabbits: Dynamic Findings of Lung Perfusion with Dual-Energy CT and Correlation with Pathologic FindingsObject:To observe dynamic changes of lung perfusion of the acute PE and with the gold standard in pathology,to evaluate the value of diagnosing acute PE of dual-energy perfusion imaging by dual-source CT.Materials and Methods:1.New Zealand rabbits(n=26) were divided into 4 groups according to different embolization time(i.e.2h group = 6,1d group = 6, 3d group = 7,7d,respectively),and underwent dual-source CT to confirm them healthy first.The scan protocol consisting of a standard unenhanced scan and a contrast enhancement with iodixanol(300mg/ml) were performed.The contrast enhancement scan was acquired in the dual-energy model.2.After undergoing the dual-source CT,the experimental pulmonary model was made.A vascular sheath was pricked into the exosing the right femoral vena of the rabbit.4 strip gelatin sponges were injected as embolis(4×4×10) mm and(2×4×10) mm.Then the model of PE was demonstrated successfully.3.Twenty-four experimental rabbits model were made successfully,And the rabbits were killed in appointed time(2h, 1d,3d,and 7d group) after underwent dual-source CT again.4.After completing the dual source CT imaging,the rabbits were killed by intravenously injecting an excessive dose of thiopental sodium.The lung were removed and fixed.The fixed lungs were sliced in a transverse plane.The location and number of the embolism in these slices were recorded on a per lobe basis.5.On the workstation,the image processing and imaging evaluation were made.Based on the pathology,all images including pre-and post-embolization were analyzed by lung PBV software. CTPA,dual energy perfusion imaging(DEPI),and fusion images were obtained. To observe the dynamic changes of lung perfusion,the numbers and locations of PE in DEPI,CTPA,and fusion images were recorded in a per lobe basis;the location and number of the embolism in these slices were recorded.With the pathology as the reference standards,Sensitivity(SE),Specificity(SP),Positive predictive value(PPV),and Negative predictive value(NPV) of CTPA,DEPI, and fusion images were measured.The value of CT in the embolic and non-embolic areas in enhanced CT after embolization was compared.6.Analysis of all data was carried out by statistical SPSS13.0.With the pathology as the reference standards,The McNamara Test was used to evaluate the accuracy of all methods respectively.Kappa analysis was used to determine the agreement between each method and pathology.The Independent-Samples T test was used to compare the differences between the values of CT in the embolic and non-embolic areas.Results:On the DEPI,lung appeared as uniform red before embolization;blue at 2h after embolization;blue and black at 1d and 3d;and black at 7day.With the pathology as a standard of reference,the SE,SP,PPV,and NPV of CTPA were 100%,95%,95%,100%(Kappa=0.950),respectively,the SE,SP,PPV,and NPV of DEPI were 98%,100%,100%,99%(Kappa=0.983),respectively.In the enhanced CT scans,there were significant difference for CT values between embolism and non-embolism areas after 2h(t=-4.471,P=0.000) and after 1day (t=-3.444,P=0.002);but there was no significant difference for CT values after 3day(t=0.273,P=0.787) and after 7day(t=0.145,P=0.886) Conclusion1) The method of preparation of acute pulmonary embolism of rabbits by using gelatin sponge as embolus is simple,and with high successful rate,it provides a good experimental model for imaging study on pulmonary embolism;2) Dual-source,dual-energy CT perfusion imaging of pulmonary embolism can observe the perfusion lung dynamic changes in real terms after embolism;3) After embolism,dual-energy CT perfusion imaging can show a series of changes from perfusion sparse to perfusion missing,corresponding to pathological manifestations from early lung pulmonary oligemia to consolidated and infarction in an experimental rabbit of pulmonary embolism;4) Dual-source,dual-energy.CT pulmonary perfusion imaging technology of pulmonary embolism in rabbit model is highly sensitive,which were correlated well with the pathologic findings. Part TwoDual-Energy CT Lung Perfusion Imaging—Correlation to Perfusion Scintigraphy in An Experimental Rabbit Model of Acute Pulmonary EmbolismObjective:To evaluate the diagnostic value of dual-energy CT lung perfusion imaging and perfusion scintigraphy in acute pulmonary embolism(PE) rabbit model compared with the pathology as reference standardMethods:Of 24 rabbits,20 experimental rabbit models of acute PE were established by femoral vein injection of sponge as embolus materials,4 rabbits in contrast group were injected saline by catheter.After embolization 2h, Dual-energy CT and perfusion scintigraphy were performed,respectively.They were killed later.With the pathology results as the reference standards,the sensitivity,specificity,PPV,and NPV of the both imaging modalities were computed.CT numbers and enhancement degree(Overlay value) of the embolic areas and normal pulmonary parenchyma were measured in DEPI image after embolization.Two independent sample nonparametric and independent sample student t tests were used to compare difference of CT values and Overlay values. Analysis of all data was done by using the statistical software of SPSS13.0.Results:On the DEPI,the lung of control group appeared as uniform red and blue of experimental rabbit models at 2h after embolization.The perfusion of embolism areas was rarefaction or absence using scintigraphy.With pathology as a standard of reference,the SE,SP,PPV,and NPV of DEPI were 100%,94%,89%,100%, respectively;86%,92%,86%,92%for perfusion scintigraphy;respectively.After embolism,there was significant difference for CT values of DEPI images between embolism and non-embolism areas(z=-5.948,P=0.000).There was significant difference for overlay values between the embolic and non-embolic areas(t=-14.173,P=0.000)Conclusion1) Perfusion scintigraphy can show the distribution of pulmonary blood flow;2) Perfusion scintigraphy is a sensitive technology to detect pulmonary embolism, but not provide anatomical information;3) The sensitivity and specificity of dual source,dual energy perfusion imaging is higher than those of perfusion scintigraphy for the detection of PE in an experimental rabbit model of acute pulmonary embolism;4) Dual source,dual-energy CT perfusion imaging can provide morphological and functional information of the whole lungs,it is able to improve the diagnostic accuracy of pulmonary embolism by comprehensive analysis of two types of images.