The Clinical Application Of Combined Dual-energy CT Pulmonary Angiography And Indirect CT Venography

Part one:The clinical application of combined dual-energyCT pulmonary angiography and indirect CT venographyObjective:To assess the clinial application of combined dual-energy CT pulmonary angiography(DE-CTPA) and indirect CT venography （CTV） in the diagnosis of venousthromboembolism (VTE).Methods:Forty nine patients with leg swelling suspected of pulmonary embolism (PE) fromSeptember2011to March2012underwent DE-CTPA combined with CTV. All ofthem has taken lower extremity venous ultrasound (US) in1week ahead of CTexamination. DE-CTPA images and CTV images were analysed according to therelated diagnostic criteria, then the arterial enhancement of pulmonary trunk wasrecorded as well as the attenuation value of the thrombus. Recorded the number andlocation of filling defects in the dual energy perfusion image (DEPI). Subjectiveimage quality of CTPA and DEPI was rated using a5-point scale by two experiencedexpertises. The coherence between them was analysed by Kappa statistics. Thecoherence of findings between CTV and US in the ability to diagnose deep venousthrombosis （DVT）was analysed by Paired Chi-square test. The radiation dose of thecombined scanning protocol was recorded and calculated.Results:1. Twenty nine patients were identified with PE by DE-CTPA, including28patientsidentified by CTPA and one more by DEPI, and21patients with both PE and DVT.Both DE-CTPA and DEPI had positive findings for pulmonary embolism in19patients and both had negative findings in18patients. 2. Eighty six filling defects were found in DEPI, compared with outcome of CTPA,there was a moderate agreement between assessment of DEPI and DE-CTPA(Kappa value=0.7534).3. Thirty eight patients with DVT were identified by US,11patients were identifiednegative by US while10were identified negative by CTV. No significantlystatistical difference was detected between assessment of CTV and US in thediagnosis of DVT（P=0.625）. The detection rate of VTE with DE-CTPAcombined CTV was30.6%higher than that with CTPA alone.4. DLP of DE-CTPA was （322.4±40.0） mGy·cm, ED was（4.5±0.6） mSv; DLPof CTV was（127.3±38.4） mGy·cm.Conclusion:The combined DE-CTPA and CTV achieves “one-stop” examination, not onlyproviding evaluation of PE and DVT and increasing detection of VTE, but alsodepicting perfusion defect of pulmonary parenchyma that correspond to PE. Part two:Low radiation exposure in indirect CT venographyfor diagnosis of venous thromboembolism with differenttube voltages: comparison of80kVp and100kVpObjective:To prospectively explore feasibility of low radiation exposure protocol in indirect CTvenography (CTV) by using a lower tube voltage of80kilovolt (peak)(kVp) compared with standard tube voltage of100kVp in diagnosis of venousthromboembolism (VTE).Materials and Methods:Ethic committee of hospital and informed consent was obtained. Eighteen patientswith leg swelling suspected of pulmonary embolism (PE) underwent CT pulmonaryangiography (CTPA) combined with CTV of pelvis and lower extremities. Twoperiods CTV of each patient was scanned by using different tube voltages,80kVpwith delay time of120s,100kVp with180s respectively after CTPA. Radiation doseparameters, femoral vein and popliteal vein enhancement, attenuation values ofgluteus maximus (Agluteus maximus) and its standard deviation (SD) were measured tocalculate signal-to-noise ratio (SNR). SD was defined to represent image noise. Tworadiologists who were blinded to different protocols assessed image quality by using a5-point scale. Statistical analysis was performed using non-parameric Wilcoxon ranktest and Paired t test. The intraclass correlation coefficient was used to testinterobserver agreement of image quality between two protocols.Results:Even though the noise in80kVp was significantly higher than that in100kVp(26.41±4.42versus18.98±2.26), Image quality scores of two protocols had nosignificant difference，while radiation dose of80kVp was significantly lower thanthat of100kVp.Conclusion:Tube voltage reduction from100kVp to80kVp in indirect CTV leads to an apparentdecrease of radiation dose by more than50%without significant impairment ofimage quality.