A Combinationof Energy Spectrum CT Imaging With Iterative Reconstruction Technique In The Diagnosis Of Pulmonary Embolism

Objective(1)To explore the feasibility of pulmonary angiography(CTPA)with 7.0g iodine contrast medium under low-energy(40 and 50kev)virtual monochromatic(VMC)images with rapid-kilovoltage-switching dual-energy CT can asure the image quality or not.(2)To explore the diagnostic value of the energy spectrum CTPA 40 kev single-energy image combined with iodine-based substance map in patients with pulmonary embolism.Methods (1)Part 1: A total of 123 adults with suspected pulmonary embolism were enrolled in this study and received CT examination under GE Revolution CT system.Subjects were randomly assigned to a contrast medium protocol for CTPA examinations: groupone(n=41)received 14.0g iodine with an standard DE CTPA protocol,group 2(n=41)received 7.0g iodine with a low CM injection DE CTPA protocol,and group 3(n=41)received 17.5g iodine with a standard CTPA protocol.DE CTPA uses 50% ASIR-V and 200 mAs scanning to reduce radiation dose.Two readers independently assessed the image quality of the CTPA and VMC DE CTPA datasets using the 5-point scale.CT attenuation,SNR,CNR and subjective evaluation were compared between the three groups.(2)Part 2: Fifty two patients with clinically highly suspected pulmonary embolism underwent Revolution CT enhanced scaning and 20 patients were diagnosed with pulmonary embolism.The emboli were analyzedwere with the post-processing technique such as maximal intensity projection(MPR),multi-level reformation(MIP),and volume rendering technique.The embolis were recorded by the number,distribution and type of emboli from the obtained conventional CTPA image.The energy spectrum data were analyzed with the GSI Viewer software package and acquire 40-140 kev virtual monoenergetic images.The number,distribution and type of emboli were recorded accordingtothe 40 kev single-energy image.The iodine/water substance was separated by energy spectrum data and the iodine-based material map were obtained from the energy spectrum data,and the lung perfusion defect area was recorded according tothe iodine-based substance map.The iodine content of the embolization area was measured in the region of interest,and the contralateral normal area was selected as the control.When the contralateral area was embolized,the ipsilateral normal area was selected as the control.A comparison of the diagnostic accuracy was made between the energy spectrum CTPA 40 kev single energy image combined with iodine-based substance map and conventional CTPA.Results (1)Part 1: Virtual monoenergetic spectral datasets(40-140kev)were reconstructedfrom DECTPA succesfully.No great differenceof the CT attenuation in main and lobar pulmonary arteryat 50 kev was found between the group of DE CTPA with low dose ofcontrast media(444.5+185.7)and the standard CTPA protocol group(455.1+126.3)(p=0.603).However,Main and lobar pulmonary arteries at 40 kev datasets provided the highest signal-to-noise-ratio(SNR)and contrast-to-noise-ratio(CNR)for both the standard DE CTPA protocol and the low CM injection protocol.the standard DE CTPA protocol had significantly higher CNR and SNR values than the standard CTPA protocol(p<0.05),which the low CM DE CTPA was slightly lower than the standard CTPA,while its subjective score meets the diagnostic requirements.No pulmonary embolism was missed on the three protocols.Comparing the radiation doses of the three groups,the DECTPA group was significantly lower than the standard CTPA group,and the difference was statistically significant.(2)Part 2:On the basis of CTPA,20 patients were diagnosed with pulmonary embolism,and 118 emboli were found,including 4(3.4%)in main pulmonary artery,30(25.4%)in lobar pulmonary artery,52(44.1%)in segmental pulmonary artery,and 32(27.1%)in sub-segmental pulmonary artery.On CTPA,twenty-seven emboli(22.9%)are occlusive emboli,while 91 cases(70.2%)are non-occlusive emboli.However,a total of 125 emboli were detected in 40 kev single-energy images,which include 4(3.2%)in main pulmonary artery,30(24%)in lobar pulmonary artery,55(44%)in segmental pulmonary artery and 36(28.8%)in sub-segmental pulmonary artery.On40 kev single-energy images,34 emboli(27.2%)are occlusive,while 91 are non-occlusive emboli(72.8%).Seven emboli in segmental and sub-segmental pulmonary artery weredemonstrated on 40 kev single-energy image onlycompared with the mixed-energy image,and all these 7 additional emboli happened on patients with poor enhancement.Compared with conventional mixed energy CTPA,The CT valuein the lumen,the SNR and CNR had been improved greatly in 40 kev virtual monochromatic image.Compared with the control group,the iodine value in the embolization area is lower with great significance.Conclusion(1)A combinationof energy spectrum CT imaging with iterative reconstruction techniquecan help reduce the total iodine amount to 7.0g(reduction of 60%)and the total radiation exposure(reduction of 78%)and ensure adequate intravascular attenuation and diagnositic quality for pulmonary embolism evaluation.(2)A combination of virtual monochromatic dual-Energy pulomonary CT angiography at 40 kev with iodine-based substance map can help improve the diagnostic accuracy of pulmonary embolism and increase the diagnostic confidence,especially for patients with pulmonary embolism with poor enhancement.In summary,virtual monochromatic dual-Energy pulomonary CT angiography imaging can reduce the usage of contrast agent and radiation dose and ensure image quality.The CTPA single energy imaging and iodine-based substance map can help each other and improve the diagnosis of pulmonary embolism.The dual energy spectrum CTPA as an effective diagnostic tool for pulmonary embolism can be widely used in clinical practice.