Rationale and Objectives
The aim of this study was to investigate whether 80-kVp and weighted-average 120-kVp computed tomographic (CT) images scanned at 60 seconds after contrast material injection using a dual-source CT scanner could substitute for conventional 120-kVp images obtained at 30 and 100 seconds.
Materials and Methods
Eighty-three consecutive patients with suspected lung cancer were enrolled. Images were obtained in dual-energy mode (80 and 140 kVp) at 60 seconds and conventional 120-kVp mode at 30 and 100 seconds after contrast injection. The CT numbers of the pulmonary artery, pulmonary vein, hilar zone lymph nodes, and pulmonary lesions were measured. Contrasts between the pulmonary artery/pulmonary vein and lymph nodes and beam-hardening artifacts were visually evaluated using five-point and four-point scales, respectively. The degree of enhancement was evaluated on 30-second 120-kVp, 100-second 120-kVp, and 60-second weighted-average 120-kVp images.
Results
The mean differences in attenuation between the pulmonary artery/pulmonary vein and lymph nodes on the 30-second 120-kVp, 60-second 80-kVp, and 60-second weighted-average 120-kVp images were 184/155, 130/140, and 84/92 Hounsfield units, respectively (all P values <.001). The mean contrast scores for the hilar/mediastinal lymph nodes were 4.5/4.7, 3.7/4.2, 3.3/3.6, and 2.4/2.5 for these three and for 100-second 120-kVp images, respectively (all P values <.01). The mean artifact scores of the four images were 1.2, 3.4, 3.6, and 4.0, respectively. On 60-second weighted-average 120-kVp images, 55 of 60 lesions (92%) showed higher enhancement than on 100-second conventional 120-kVp images.
Conclusions
Dual-energy CT images scanned 60 seconds after contrast injection show excellent vessel–lymph node contrast and enhancement of lesions and can replace dual-phase scan protocols.
Evaluation of metastases to regional lymph nodes (LNs) is very important to predict the prognoses of patients with lung cancer and to establish treatment strategies. Contrast-enhanced (CE) computed tomographic (CT) imaging is the standard modality for this purpose. It has been reported that scanning soon after contrast material injection (eg, 30 seconds) is appropriate for clearly depicting the hilar and mediastinal LN . However, this is too early to evaluate the contrast enhancement of pulmonary lesions such as neoplasms, inflammations, and tuberculomas. At our institution, therefore, postcontrast scans have been performed twice: at an early phase (30 seconds) to evaluate the LNs and at a late phase (100 seconds) to evaluate the vascularity of lesions. However, it is desirable that both demands be fulfilled with a single scan.
With a dual-energy (DE) CT scanner, images at low and high tube voltages can be obtained at one time. Using a low tube voltage, the contrast between iodinated contrast medium and surrounding tissues becomes larger because iodine provides greater x-ray attenuation, caused by the increase in its relative atomic number ( Z = 53) upon exposure to reduced x-ray energy . The photoelectric effect in x-ray attenuation increases at lower tube voltages, particularly in scans of structures with high effective atomic numbers. Because of Compton scattering, most x-rays interact to a lesser extent with soft tissue as tube voltage increases. Therefore, tube voltage reduction leads to an increase in the attenuation of calcified structures and iodinated contrast material as the photoelectric effect increases and Compton scattering decreases. Consequently, as the k-edge of iodine is closer to the reduced voltage, beam attenuation is increased, and higher attenuation readings are obtained . It has been reported that chest multi–detector row CT scans at low tube voltages can reduce radiation dose, with images showing improved contrast enhancement . On the other hand, CT images scanned at low tube voltages result in reduced quality by increasing the level of noise and artifacts. Increases in image noise with the use of lower tube voltages lead to a direct reduction in photon flux , but no significant differences have been reported in image noise and radiation dose between single-energy acquisition and weighted-average 120-kVp DE images generated from a combination of 80-kVp and 140-kVp images .
Get Radiology Tree app to read full this article<
Materials and methods
Study Design
Get Radiology Tree app to read full this article<
Patients
Get Radiology Tree app to read full this article<
CT Scanning
Get Radiology Tree app to read full this article<
Evaluation of Images
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
Results
Objective Assessment
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
Visual Assessment
Get Radiology Tree app to read full this article<
Table 1
Scores for Visual Assessment of Contrast between the Pulmonary Vessels and Lymph Nodes
Lymph Node Image Scan Delay (s) Tube Voltage (kVp) Observer 1 Observer 2 Observer 3 Main bronchial 30 120 4.6 ± 0.7 (2–5) 4.7 ± 0.6 (2–5) 4.4 ± 0.9 (2–5) 60 80 4.0 ± 0.6 (3–5) 4.0 ± 0.7 (2–5) 3.6 ± 1.0 (1–5) 60 120 3.4 ± 0.7 (2–5) 3.7 ± 0.8 (1–5) 3.0 ± 0.8 (1–5) 100 120 2.3 ± 0.7 (1–5) 3.1 ± 0.8 (1–5) 2.1 ± 0.9 (1–5) Interlobar 30 120 4.4 ± 0.9 (2–5) 4.7 ± 0.6 (2–5) 4.5 ± 0.8 (2–5) 60 80 3.6 ± 0.7 (2–5) 4.1 ± 0.7 (2–5) 3.8 ± 0.9 (2–5) 60 120 3.1 ± 0.7 (1–5) 3.6 ± 0.9 (1–5) 3.3 ± 0.8 (2–5) 100 120 2.1 ± 0.6 (1–5) 3.1 ± 0.8 (1–5) 2.4 ± 0.8 (1–5) Lobar 30 120 3.7 ± 1.1 (1–5) 4.7 ± 0.5 (3–5) 4.4 ± 0.8 (2–5) 60 80 2.8 ± 0.9 (1–5) 4.0 ± 0.7 (2–5) 3.7 ± 0.9 (2–5) 60 120 2.3 ± 0.8 (1–5) 3.6 ± 0.8 (2–5) 3.0 ± 0.8 (1–5) 100 120 1.3 ± 0.6 (1–5) 3.0 ± 0.8 (1–5) 2.0 ± 0.8 (1–5) Mediastinal 30 120 4.8 ± 0.5 (3–5) 4.8 ± 0.5 (3–5) 4.5 ± 0.8 (2–5) 60 80 4.4 ± 0.7 (2–5) 4.3 ± 0.7 (3–5) 3.8 ± 0.9 (1–5) 60 120 4.0 ± 0.7 (2–5) 3.8 ± 0.8 (1–5) 3.2 ± 0.8 (2–5) 100 120 2.5 ± 0.6 (2–5) 2.9 ± 0.7 (1–5) 2.1 ± 0.8 (1–5)
Data are expressed as mean ± standard deviation (range). All P values between any pair of the four images were <.05 in all lymph nodes for three observers.
Table 2
Scores for Visual Assessment of Beam-hardening Artifacts
Observer Image Scan Delay (s) Tube Voltage (kVp) Mean ± Standard Deviation (Range) 1 30 120 1.3 ± 0.7 (1–4) 60 80 3.5 ± 0.5 (2–4) 60 120 3.6 ± 0.5 (2–4) 100 120 3.9 ± 0.2 (3–4) 2 30 120 1.3 ± 0.8 (1–4) 60 80 3.7 ± 0.4 (3–4) 60 120 3.8 ± 0.4 (3–4) 100 120 4.0 ± 0.2 (3–4) 3 30 120 1.1 ± 0.4 (1–3) 60 80 3.0 ± 0.6 (1–4) 60 120 3.4 ± 0.6 (1–4) 100 120 4.0 ± 0.1 (3–4)
Get Radiology Tree app to read full this article<
Representative Cases
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
![Figure 7, Case 2, a 63-year-old woman with pulmonary squamous cell carcinoma on unenhanced, 30-second, 60-second weighted-average (WA), and 100-second 120-kVp images (window width, 360 Hounsfield units [HU]; window level, 60 HU). The lesion shows a peak enhancement of 100 HU on the 60-second weighted-average 120-kVp image, and the contrast is distinct compared to that of an unenhanced image (29 HU). On the 30-second and 100-second 120-kVp images, the lesion shows less enhancement (46 and 45 HU, respectively), and the contrast between unenhanced and enhanced images is not evident.](https://storage.googleapis.com/dl.dentistrykey.com/clinical/DualenergyCTCanEvaluateBothHilarandMediastinalLymphNodesandLesionVascularitywithaSingleScanat60SecondsafterContrastMediumInjection/6_1s20S1076633212001778.jpg)
Get Radiology Tree app to read full this article<
Discussion
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
Get Radiology Tree app to read full this article<
Conclusions
Get Radiology Tree app to read full this article<
References
1. Shimoyama K., Murata K., Takahashi M., et. al.: Pulmonary hilar lymph node metastases from lung cancer: evaluation based on morphology at thin-section, incremental, dynamic CT. Radiology 1997; 203: pp. 187-195.
2. Kaiser L.R., Shrager J.B.: Video-assisted thoracic surgery: the current state of the art. AJR Am J Roentgenol 1995; 165: pp. 1111-1117.
3. Yano T., Yokoyama H., Inoue T., et. al.: Surgical results and prognostic factors of pathologic N1 disease in non-small-cell carcinoma of the lung. Significance of N1 level: lobar or hilar nodes. J Thorac Cardiovasc Surg 1994; 107: pp. 1398-1402.
4. Glazer G.M., Gross B.H., Aisen A.M., et. al.: Imaging of the pulmonary hilum: a prospective comparative study in patients with lung cancer. AJR Am J Roentgenol 1985; 145: pp. 245-248.
5. Watanabe Y., Hayashi Y., Shimizu J., et. al.: Mediastinal nodal involvement and the prognosis of non-small cell lung cancer. Chest 1991; 100: pp. 422-428.
6. Johnson T.R., Krauss B., Sedlmair M., et. al.: Material differentiation by dual energy CT: initial experience. Eur Radiol 2007; 17: pp. 1510-1517.
7. Nakayama Y., Awai K., Funama Y., et. al.: Abdominal CT with low tube voltage: preliminary observations about radiation dose, contrast enhancement, image quality, and noise. Radiology 2005; 237: pp. 945-951.
8. Chae E.J., Song J.W., Seo J.B., et. al.: Clinical utility of dual-energy CT in the evaluation of solitary pulmonary nodules: initial experience. Radiology 2008; 249: pp. 671-681.
9. McCollough C.H., Primak A.N., Saba O., et. al.: Dose performance of a 64-channel dual-source CT scanner. Radiology 2007; 243: pp. 775-784.
10. Yeh B.M., Shepherd J.A., Wang Z.J., et. al.: Dual-energy and low-kVp CT in the abdomen. AJR Am J Roentgenol 2009; 193: pp. 47-54.
11. Sigal-Cinqualbre A.B., Hennequin R., Abada H.T., et. al.: Low-kilovoltage multi-detector row chest CT in adults: feasibility and effect on image quality and iodine dose. Radiology 2004; 231: pp. 169-174.
12. Swensen S.J., Yamashita K., McCollough C.H., et. al.: Lung nodules: dual-kilovolt peak analysis with CT—multicenter study. Radiology 2000; 214: pp. 81-85.
13. Thieme S.F., Johnson T.R., Lee C., et. al.: Dual-energy CT for the assessment of contrast material distribution in the pulmonary parenchyma. AJR Am J Roentgenol 2009; 193: pp. 144-149.
14. Graser A., Johnson T.R., Chandarana H., et. al.: Dual energy CT: preliminary observations and potential clinical applications in the abdomen. Eur Radiol 2009; 19: pp. 13-23.
15. Schenzle J.C., Sommer W.H., Neumaier K., et. al.: Dual energy CT of the chest: how about the dose?. Invest Radiol 2010; 45: pp. 347-353.
16. Imafuji A., Hara M., Sasaki S., et. al.: Usefulness of dual-energy CT scanning at 80 kVp for identifying hilar and mediastinal structures: evaluation of contrast enhancement of the pulmonary vessels and lymph nodes. Jpn J Radiol 2012; 30: pp. 69-77.
17. Littleton J.T., Durizch M.L., Moeller G., et. al.: Pulmonary masses: contrast enhancement. Radiology 1990; 177: pp. 861-871.
18. Tateishi U., Nishihara H., Watanabe S., et. al.: Tumor angiogenesis and dynamic CT in lung adenocarcinoma: radiologic-pathologic correlation. J Comput Assist Tomogr 2001; 25: pp. 23-27.
19. Kawai T., Shibamoto Y., Hara M., et. al.: Can dual-energy CT evaluate contrast enhancement of ground-glass attenuation? Phantom and preliminary clinical studies. Acad Radiol 2011; 18: pp. 682-689.