Objectives
This study aimed to intra-individually and inter-individually compare image quality, radiation dose, and diagnostic accuracy of dual-source dual-energy computed tomography pulmonary angiography (CTPA) protocols in patients with suspected pulmonary embolism (PE).
Methods
Thirty-three patients with suspected PE underwent initial and follow-up dual-energy CTPA at 80/Sn140 kVp (group A) or 100/Sn140 kVp (group B), which were assigned based on tube voltages. Subjective and objective CTPA image quality and lung perfusion map image quality were evaluated. Diagnostic accuracies of CTPA and perfusion maps were assessed by two radiologists independently. Effective dose (ED) was calculated and compared.
Results
Mean computed tomography (CT) values of pulmonary arteries were higher in group A than group B ( P = .006). There was no difference in signal-to-noise ratio and contrast-to-noise ratio between the two groups (both P > .05). Interobserver agreement for evaluating subjective image quality of CTPA and color-coded perfusion images was either good (κ = 0.784) or excellent (κ = 0.887). Perfusion defect scores and diagnostic accuracy of CTPA showed no difference between both groups (both P > .05). Effective dose of group A was reduced by 45.8% compared to group B ( P < .001).
Conclusions
Second-generation dual-source dual-energy CTPA with 80/Sn140 kVp allows for sufficient image quality and diagnostic accuracy for detecting PE while substantially reducing radiation dose.
Introduction
Acute pulmonary embolism (PE) ranks as the third most common cardiovascular condition, after coronary artery disease and stroke . Due to the nonspecific clinical symptoms, imaging plays an important role in detection and follow-up of acute PE . Currently, computed tomography pulmonary angiography (CTPA) is considered the reference standard in diagnosis of acute PE . Dual-energy CTPA is capable of providing anatomic, perfusion, ventilation, and pulmonary vascular tree information for the whole lung, which makes it an important tool for comprehensive evaluation of PE .
With the application of dual-energy computed tomography (CT) in the lungs, diagnostic accuracy for acute and chronic PE, as well as other vascular disorders such as lung malignancies and parenchymal diseases, has been improved . Compared to routine single-energy CTPA, dual-energy CTPA showed advantages in detecting small peripheral PE . With concerns regarding radiation risk, the clinical use of CTPA has increasingly come into focus. Thieme et al. indicated that according to the European guidelines on quality criteria for CT, the radiation dose with first-generation dual-source dual-energy CTPA (80/140 kVp) is lower than the reference value of 650 mGy⋅cm. With the development of second-generation dual-source CT, multiple scanning parameters of dual-source dual-energy CTPA, such as 80/Sn140 kVp and 100/Sn140 kVp, can be selected. Recently, Bauer et al. demonstrated that second-generation dual-energy CT with 80/Sn140 kVp allowed for significant dose reduction with the same image quality compared to 120 kVp CTPA. However, this study did not include an intra-individual comparison and did not analyze lung perfusion images. Both Thieme et al. and Bauer et al. provide important information for the diagnosis and prognosis evaluation of PE . Thus, further studies seem warranted to expand on these aspects. The purpose of this study was to intra-individually and inter-individually compare image quality, radiation dose, and diagnostic accuracy of dual-energy CTPA with the two different scanning parameters, and determine the optimized scanning protocols for dual-energy CTPA in clinical routine.
Materials and Methods
Patients
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CT Scanning Protocol
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Dual-Energy CTPA Image Quality Evaluation
Objective Image Quality Evaluation
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Subjective Image Quality Evaluation
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Dual-Energy Lung Perfusion Image Evaluation
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Detection of Pulmonary Emboli
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Radiation Dose Estimation
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Statistical Analysis
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Results
Subjects
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Dual-Energy CTPA Image Quality Evaluation
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Table 1
Objective Image Quality Measurements in the Two CTPA Groups
Location Group A Group B_P_ Value MPA CT number (HU) \* 386.3 ± 94.1 318.2 ± 94.8 .003 SNR 41.4 ± 12.4 46.3 ± 16.5 .145 CNR 36.0 ± 11.7 38.6 ± 15.7 .419 RPA CT number (HU) \* 357.0 ± 86.3 302.5 ± 92.7 .008 SNR 38.2 ± 11.0 44.1 ± 16.2 .064 CNR 32.8 ± 10.4 36.3 ± 15.4 .235 LPA CT number (HU) \* 366.9 ± 91.9 307.7 ± 95.3 .007 SNR 39.3 ± 11.7 44.8 ± 16.2 .102 CNR 33.8 ± 11.1 37.1 ± 15.4 .315 RULA CT number (HU) \* 373.8 ± 96.9 302.4 ± 108.2 .003 SNR 40.1 ± 12.3 44.0 ± 17.2 .257 CNR 34.6 ± 11.6 36.2 ± 16.5 .628 RILA CT number (HU) 340.6 ± 96.6 301.5 ± 110.4 .075 SNR \* 36.2 ± 10.7 43.8 ± 17.2 .031 CNR 30.8 ± 10.4 36.0 ± 16.5 .114 LULA CT number (HU) \* 366.7 ± 102.2 299.1 ± 106.2 .006 SNR 39.3 ± 12.7 43.4 ± 15.9 .251 CNR 33.8 ± 12.0 35.6 ± 15.3 .608 LILA CT number (HU) \* 356.1 ± 95.9 303.8 ± 107.4 .007 SNR \* 38.0 ± 11.2 44.2 ± 16.5 .047 CNR 32.5 ± 10.7 36.4 ± 15.8 .184 Mean CT number (HU) \* 363.9 ± 90.7 305.0 ± 100.4 .006 SNR 38.9 ± 11.3 44.4 ± 16.3 .099 CNR 33.5 ± 10.7 36.6 ± 15.5 .317 Muscle (HU) 50.7 ± 9.7 53.6 ± 7.5 .125 Noise (HU) \* 9.6 ± 1.4 7.1 ± 1.3 <.001
CNR, contrast-to-noise ratio; CT, computed tomography; CTPA, computed tomography pulmonary angiography; HU, Hounsfield units; LILA, left inferior lobe pulmonary artery; LPA, left main pulmonary artery; LULA, left upper lobe pulmonary artery; MPA, main pulmonary artery; RILA, right inferior lobe pulmonary artery; RPA, right main pulmonary artery; RULA, right upper lobe pulmonary artery; SNR, signal-to-noise ratio.
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Table 2
Subjective Image Quality Evaluation in the Two Dual-Energy CTPA Groups
Readers Group A Group B_P_ Value CTPA images Reader 1 1.09 ± 0.05 1.06 ± 0.04 .655 Reader 2 1.06 ± 0.04 1.03 ± 0.03 .564 Kappa value 0.784 0.653 – Perfusion images Reader 1 2.64 ± 0.49 2.79 ± 0.42 .096 Reader 2 2.67 ± 0.48 2.79 ± 0.42 .157 Kappa value 0.933 0.819 –
CTPA, computed tomography pulmonary angiography.
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Dual-Energy Lung Perfusion Image Quality Evaluation
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Detection of Pulmonary Emboli
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Table 3
Pulmonary Emboli Detected by Two Readers
True Positive False Negative False Positive True Negative Group A Group B Group A Group B Group A Group B Group A Group B Patients Reader 1 17 19 1 0 2 1 13 13 Reader 2 17 17 1 2 1 0 14 14 Central PE Reader 1 21 22 1 0 4 2 271 273 Reader 2 21 20 2 2 2 1 272 274 Peripheral PE Reader 1 42 20 8 5 2 1 608 634 Reader 2 39 18 11 7 4 1 606 634
PE, pulmonary embolism.
The data for the central arteries refer to the number of affected main and lobar pulmonary arteries. The data for the peripheral arteries refer to the number of affected pulmonary segmental and subsegmental arteries.
Table 4
Diagnostic Accuracy Comparison of the Two CTPA Protocols
Sensitivity Specificity PPV NPV Accuracy_P_ Value Group A Group B Group A Group B Group A Group B Group A Group B Group A Group B Patient Reader 1 94.4
(74.2–99.0) 100
(83.2–100) 86.7
(62.1–96.3) 92.9
(68.5–98.7) 89.5
(76.4–99.1) 95.0
(76.4–99.1) 92.9
(68.5–98.7) 100
(77.2–100) 90.9
(76.4–96.9) 97.0
(84.7–99.5) .30 Reader 2 94.4
(74.2–99.0) 89.5
(68.6–97.1) 93.3
(70.2–98.8) 100
(78.5–100) 94.4
(74.2–99.0) 100
(81.6–100) 93.3
(70.2–98.8) 87.5
(64.0–96.5) 93.9
(80.4–98.3) 93.9
(80.4–98.3) 1 Central PE Reader 1 95.5
(78.2–99.2) 100
(85.1–100) 98.5
(96.3–99.4) 99.3
(97.4–99.8) 84.0
(65.4–93.6) 91.7
(74.2–97.7) 99.6
(98.0–99.9) 100
(98.6–100) 98.3
(96.1–99.3) 99.3
(97.6–99.8) .25 Reader 2 91.3
(73.2–97.6) 90.9
(72.2–97.5) 99.3
(97.4–99.8) 99.6
(98.0–99.9) 91.3
(73.2–97.6) 95.2
(77.3–99.2) 99.3
(97.4–99.8) 99.3
(97.4–99.8) 98.7
(96.6–99.5) 99.0
(97.1–99.7) .70 Peripheral PE Reader 1 84.0
(71.5–91.7) 80.0
(60.9–91.1) 99.7
(98.8–99.9) 99.8
(99.1–100) 95.5
(84.9–98.7) 95.2
(77.3–99.2) 98.7
(97.5–99.3) 99.2
(98.2–99.7) 98.5
(97.2–99.2) 99.1
(98.0–99.6) .31 Reader 2 78.0
(64.8–87.3) 72.0
(52.4–85.7) 99.3
(98.3–99.7) 99.8
(99.1–100) 90.7
(78.4–96.3) 94.7
(75.4–99.1) 98.2
(96.8–99.0) 98.9
(97.8–99.5) 97.7
(96.3–98.6) 98.8
(97.6–99.4) .14
NPV, negative predictive value; PE, pulmonary embolism; PPV, positive predictive value.
Data in parentheses indicate 95% confidence interval.
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Radiation Dose Comparison
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Table 5
Radiation Dose Estimation and Comparison in This Study
Parameters Group A Group B_P_ Value CTDIvol (mGy) 3.0 ± 0.7 5.6 ± 1.5 <.001 DLP (mGy⋅cm) 93.3 ± 25.6 173.5 ± 44.9 <.001 ED (mSv) 1.3 ± 0.4 2.4 ± 0.6 <.001
CTDIvol, volume CT dose index; DLP, dose-length product; ED, effective dose.
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Discussion
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Acknowledgment
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