| Part oneThe feasibility of 70-kVp High-pitch CT Pulmonary Angiography with 40 mL Contrast AgentPurpose:To investigate the feasibility of 70 kVp high-pitch computed tomography pulmonary angiography (CTPA) using 40 ml contrast agent and sonogram affirmed iterative reconstruction (SAFIRE) compared to 100 kVp CTPA using 60 ml contrast agent and filtered back projection (FBP) by assessing image quality, radiation dose, and diagnostic accuracy of two groups.Materials and Methods:A total of eighty patients (50 men,30 women, with mean age 57 years old,age range,21-88 years old) were randomly divided into two groups. All patients referred for CTPA because of suspected PE. Forty patients (23 men,17 women, with mean age 58 years old, age range,23～85 years old) were assigned to undergo CTPA at 70 kVp with administration of 40 ml of iodine contrast medium and 3.2 pitch (70 kVp group). Another forty patients (27 men,13 women, with mean age,56 years old, age range, 21-88 years old) were assigned to undergo CTPA at 100 kVp with administration of 60 ml of iodine contrast medium and 1.2 pitch (100 kVp group). A collimation of 64x2x0.6 mm, rotation time of 0.28 s and the quality reference tube current time product of 150 mAs were used for both groups. Automatic tube current modulation (CAREDose 4D) was used for all examinations. Iodinated contrast material with a concentration of 300 mg I/mL (iopromide 300, Bayer Schering, Berlin, Germany) was injected into the antecubital vein of all patients in both groups at a flow rate of 4 mL/s followed by a 40 mL NaCl chaser bolus at the same speed. Sinogram affirmed iterative reconstruction (S AFIRE) with a medium strength level of 3 was used in 70 kVp group, whereas a filtered back projection (FBP) algorithm was used in 100 kVp group. The mean CT values and standard deviations (SD) of the main pulmonary artery (MPA), right main pulmonary artery (RPA), left main pulmonary artery (LPA), one upper and one inferior lobar pulmonary arteries, surrounding air in front of the patient and the paraspinal muscle at the level of the pulmonary trunk were measured. The size of the ROI was 2 cm2 in the MPA and 0.5-0.8 cm2 in the LPA and RPA. In the lobar arteries, the ROI was placed as large as possible to contain as much of the vessels. The attenuation in the paraspinal muscle at the level of the pulmonary trunk was measured by placing an ROI with a size of 1 cm2. Background noise was determined as the SD of surrounding air in front of the patient in an approximate 2 cm2 ROI. Signal-to-noise ratio (SNR) and contrast-to-noise (CNR) were calculated. The transverse and anteroposterior diameter of the chest at the level of pulmonary trunk of all the patients were measured. Subjective image quality was evaluated using a five-grade scale by two radiologists. For the evaluating of diagnostic accuracy, two radiologists, who were blinded to the CTA parameters and patients’ data, independently reported the presence of PE, recorded the anatomic distribution and number of any emboli in CTPA images. That 360 segments of central pulmonary arteries and 800 segments of peripheral pulmonary arteries need to be assessed in each group. Finally, to ensure the record of all clots in pulmonary arteries, a consensus reading session was performed by the same two radiologists again. In the event of disagreement, a third radiologist with more than 10 years of CTPA experience was invited to determine the final result. The final results were used as the reference standard for the evaluation of the diagnostic accuracy of the blinded assessment by each individual observer. The numbers of detected PE were recorded, and the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy for the detection of PE with 95% confidence interval in the two groups were calculated. The CT volume dose index (CTDIvol) and dose-length product (DLP) of each examination were recorded to calculate the effective dose (ED). The objective image quality (CT values, SNR, CNR, noise), radiation dose and the transverse diameters and anteroposterior diameters of the chest were compared using the independent sample t-test. The scores of subjective image quality were compared using the Mann-Whitney test. Gender and PE detection rates of both CTPA protocols between the two groups were analyzed with the chi-square test. Kappa analysis was used to assess the interobserver agreement for the subjective image quality.Results:No statistically significant differences were found regarding age, sex, transverse diameters and anteroposterior diameters of the chest between two groups. Computed tomography values, signal-to-noise ratio, and contrast-to-noise ratio of pulmonary arteries were higher in 70 kVp group compared to 100 kVp group (all P<0.001). Subjective image quality showed no difference between the two groups (1.03±0.16 vs. 1.05±0.22, P=0.559) with good interobserver agreement (k=0.647).There was no difference in the prevalence of PE between the two groups (n=7 in 70 kVp group vs. n=7 in 100 kVp group, P>0.99). A total of 720 segments of central pulmonary arteries and 1600 segments of peripheral pulmonary arteries were assessed in both groups and no difference was found regarding diagnostic accuracy between the two groups (P>0.05). The effective dose for 70 kVp group was lower by 80% and the contrast material was decreased by one third compared to 100 kVp group (P<0.001).Conclusions:70-kVp high-pitch CTPA with SAFIRE is feasible and simultaneously allows for a substantial reduction of radiation dose by approximately 80% and contrast material down to 40 mL while preserving sufficient image quality for evaluating patients with suspected PE.Part twoComparison of the two different scanning parameters of dual-source dual-energy CT pulmonary angiographyPurpose:To compare image quality, radiation dose and diagnostic accuracy of the two different scanning parameters on dual-source dual-energy (DECT) for computed tomography pulmonary angiography (CTPA) in follow-up patients who were referred for CTPA with DECT mode once because of suspected pulmonary embolism (PE). The purpose was to choose the optimal CT scanning parameters applying in clinical.Materials and Methods:A total of 33 follow-up patients (25 men,8 women; age range 13-69 years old with mean age 35 years old) with suspected PE who underwent DE-CTPA at both 80/Sn140 kV (group 1) and 100/Sn140 kV (group 2) were recruited in this study. The two groups were assigned randomly based on the different tube voltage. The quality reference tube current time product were respectively 89/38 mAs in group 1 and 89/76 mAs in group 2. Automatic tube current modulation (CAREDose 4D) was used for all examinations. A collimation of 64x2x0.6 mm, a pitch of 0.9, and rotation time of 0.28 s were used for both groups. Image acquisition automatically was triggered 6 s after the attenuation signal reached 100 Hounsfield units (HU) in the pulmonary trunk by a bolus tracking technique. The patients in both groups received 80 ml of contrast agent injection at 4 ml/s, which was followed by a 40 ml NaCl chaser bolus at the same rate. The evaluation of objective image quality was performed on the mixed series images by one observe through measuring and recording all mean attenuation values and standard deviations (SD) of the main pulmonary artery (MPA), right main pulmonary artery (RPA), left main pulmonary artery (LPA), one upper and one inferior lobar pulmonary arteries, surrounding air and the paraspinal muscle at the level of the pulmonary trunk. The signal-to-noise ratio (SNR) and contrast- to-noise ratio (CNR) were calculated. Dual energy perfusion images were reconstructed by Lung PBV software. Two radiologists reviewed all images and scored CTPA images using a 5-point scale, while scored dual energy perfusion images using a 3-point scale. For the evaluating of pulmonary perfusion defect, two radiologists reviewed all the dual energy perfusion images to record the location and number of abnormal perfusion. Perfusion defect score were calculated. For the evaluating of diagnostic accuracy, two radiologists independently reported the presence of PE, recorded the anatomic distribution and number of any emboli in CTPA images. Finally, to ensure the record of all clots in pulmonary arteries, a consensus reading session was performed by the same two radiologists again. In the event of disagreement, a third radiologist with more than 10 years of CTPA experience was invited to determine the final result. The final results were used as the reference standard for the evaluation of the diagnostic accuracy of the blinded assessment by each individual observer. The CT volume dose index (CTDIvol) and dose-length product (DLP) of each examination were recorded and effective dose (ED) were calculated. Paired-Samples t-test was used to compare CT values, CNR, SNR, noise, CTDIvol, DLP, and ED. The perfusion defect score of every group between two observers were also compared by Paired-Samples t-test. Kappa analysis was used to assess the inter-observer agreement between the two readers with respect to subjective image quality. The accuracy of both CTPA protocols for detecting PE was compared with the chi-square test.Results:The mean CT values of pulmonary arteries were higher in group 1 compared to group 2 (363.9±90.7 HU vs.305.0±100.4 HU,P=0.006), as well as the image noise (9.6±1.4 HU vs.7.1±1.3 HU, P<0.001). There was no significant difference in the mean corresponding SNR and CNR between two groups (38.9±11.3 vs.44.4±16.3, P=0.099; 33.5±10.7 vs.36.6±15.5, P=0.317). The inter-observer agreement of CTPA and dual energy perfusion images in evaluating subjective image quality were respectively good (k=0.784, P<0.001) and excellent (κ=0.887, P<0.001). No significant difference was found in perfusion defect score of every group between two observers (both P>0.05). A total of 594 segments of central pulmonary arteries and 1320 segments of peripheral pulmonary arteries were assessed. The diagnostic accuracy of PE showed no difference between both groups at each observer for central PE and peripheral PE (both P>0.05). Effective dose (ED) of group 1 was reduced by 45.8% compared to group 2 (P<0.001).Conclusions:The dual-source DECT for CTPA with 80/Sn140 kV parameters allows for a substantial reduction of radiation dose with sufficient image quality. |
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