In this study, diverse research components have been objectively analyzed to evaluate the current status of research and development trends in the applications of energy-based CT in thoracic disease. Clinically, dual-energy CT exploits two X-rays to collect energy spectra to distinguish the molecules that make up the body tissues according to their atomic number, and it has the ability to combine datasets obtained at various energy levels to achieve substance decomposition, as well as characterization [18,19,20]. Currently, six approaches exist for dual-energy imaging: single-source sequential, single-source helical, single-source twin-beam, single-source rapid switching, dual-source and dual-layer [21]. In recent years, photon-counting detector CT has technologically enabled true multi-energy CT scanning and has been applied in a number of preclinical and clinical studies [22]. The ultra-high spatial resolution of photon-counting detector CT design permits lower dose scanning for all body regions, and it is especially helpful in identifying significant imaging findings in the thoracic cavity [23]. Therefore, photon-counting detector CT is a promising technique on the verge of being clinically feasible and has the potential to dramatically change the clinical use of CT in the upcoming decades [24].

Using dual-energy CT has enhanced diagnostic confidence without being exposed to substantial radiation effects, expanding the potential of thoracic imaging in children and adults [25, 26]. Several dual-energy CT platforms can be used to generate or detect two-photon spectra of high energy and low energy, among which Canon Medical System’s two-photon spectra are obtained through different spectral acquisition techniques; GE Healthcare enables ultra-fast kvp switching, including fast switching from 80 kVp to 140 kVp, providing nearly simultaneous spatial and temporal registration of projections; Philips Medical chose to use double-layer detector technology (i.e., nano-panel prism detector), which can obtain two-photon spectra simultaneously; and for Siemens Healthineers, the two-photon spectra are acquired in the acquisition process of two different dual-energy CT platforms [27]. With the swift development of technology, interest in energy-based imaging-related applications is increasing, and radiologists have started investigating thoracic disorders in unprecedented conditions, such as analysis of bronchopulmonary disorders and cardiovascular diseases.

To the best of our knowledge, there are general or systematic reviews of dual- and multi-energy CT in thoracic disease [28,29,30] but no more well-developed bibliometric studies. Our study provides insights into the specifics of publications for each of the countries under consideration. Concerning international groups, our data reveal that the number of multiple country publications varies among the top ten countries, suggesting that collaboration is not yet widespread across countries. China, Germany, and the United States are the top three countries in terms of the number of publications, but China’s articles are cited less than the other two countries at the top of the ranking, indicating that there is still a certain gap between developing and developed countries. Further analysis of the countries of co-authorship with at least five publications was performed. There are nine clusters of different sizes, and the largest of these clusters is cluster 2, which includes the USA, China, Canada, and so on, showing that cooperation is still mostly between countries with better economic development. These countries may be more advantaged in terms of investment and development of medical resources and have been able to introduce and apply advanced medical imaging technologies, including dual-energy CT, earlier. As a result, these countries have more opportunities and capacity to conduct research in the medical field and publish their results as academic papers. The United States occupies a key position in the co-author collaboration network, indicating its relatively leading position in dual- and multi-energy CT.

An analysis of the top ten most referenced documents has been conducted to discern the significance of articles that have had a crucial impact on the scientific literature in the field we studied. These ten articles concentrate on the principles, dosage, and quality of dual-energy CT and its chest applications. The top three most cited articles were the most representative and made the greatest contribution, which deserves further in-depth analysis. The first most cited article was written in 2007 [31] by Johnson TR et al and the second most referenced literature was authored by Flohr et al in 2006 [32]; both papers demonstrate that dual-energy CT enjoys a large potential and quite a lot of conceivable clinical advantages in CT angiography. The purpose of the former was to evaluate the feasibility of using dual-energy CT to distinguish iodine from other materials and of different body tissues, while the latter demonstrated an interesting application of dual-energy CT to separate bones and iodine-filled blood vessels in CT angiography. The third most referenced article, authored by McCollough et al in 2015 [33] systematically introduces the underlying motivation and physical principles of dual- and multi-energy CT. Also, the current technical approaches and evolving clinical applications are described, laying a favorable foundation for subsequent related research. It demonstrates that dual- and multi-energy CT is steadily becoming mainstream CT imaging and has a promising future. As for scientific journals, the top two journals by h-index are European Radiology (h-index = 46) and Radiology (h-index = 36), while European Radiology emerges as the most represented source, reflecting its academic standing and high influence in the field of energy-based imaging. Of the top three most cited articles, the first and second are from European Radiology, and the third is from Radiology, so it is expected that high-quality articles with major breakthroughs are published in such excellent journals.

Trending topics showed the changes of each author’s keywords according to the timeline, which meant that the issues of dual- and multi-energy CT have changed over time. The related topics in 2008 were few and low-frequency, representing that dual- and multi-energy CT was in the preliminary application stage back then. By 2016, the application of dual-energy CT became a relatively common trend. Our analysis reveals that dual- and multi-energy CT is increasingly being applied to lungs, blood vessels, and heart. The results of the trending topics analysis show that lung-related keywords also appeared with higher frequency recently, indicating that dual-energy CT was gradually applied to the lung. In terms of lung applications, dual-energy CT can provide anatomical and functional information about the lung in diverse pulmonary disease states which can effectively improve the diagnosis of acute and chronic pulmonary embolisms, pulmonary malignancies, and lung parenchymal diseases, as well as open up new avenues for lung imaging [34]. Spectral photon-counting CT can achieve higher spatial resolution, which not only allows for earlier detection and more precise classification of pulmonary nodules, but also improves diagnostic confidence for radiologists to evaluate other lung abnormalities, such as airway and parenchymal diseases [35, 36]. The results of the thematic map analysis show that the most important dual- and multi-energy CT applications in 2020–2023 include myocardial perfusion, coronary artery disease, aortic valve stenosis, and chronic thromboembolic pulmonary hypertension. In vascular applications, dual-energy CT is supposed to break through the limitations of standard monoenergetic CT angiography, including patient exposure to carcinogenic radiation and nephrotoxic contrast agents, inadequate contrast vascular enhancement, interference from metal and beam hardening artifacts, and serious vascular calcification, as well as limited tissue characterization together with perfusion evaluation [37]. In terms of cardiac imaging evaluation, several applications of cardiac dual-energy CT, such as virtual non-contrast reconstruction, virtual single-energy images, as well as iodine myocardial perfusion diagrams, have been shown to improve both diagnostic accuracy and image quality simultaneously reduce radiation and contrast agent administration [38].

Admittedly, there are still some limitations to this analysis. Firstly, as the literature search was conducted on the 26th of October 2023, we could not cover all publications and citations in 2023, which would have led to the omission of current hot topics. Secondly, only a single database (the Web of Science Core Collection) was retrieved in this study, making the results relatively biased. In the future, other databases such as PubMed and Scopus can be jointly used to obtain more objective and comprehensive results. Additionally, the possibilities for designing a search strategy are diverse, resulting in some publications not being considered and a bias in the number of citations, which may at least partially affect the results of our findings.

The bibliometric examination offers a comprehensive summary of the current status and benefits of dual- and multi-energy CT, paving the way for future clinical diagnostic and analytical applications in thoracic disease. Notably, dual- and multi-energy CT has witnessed rapid development in recent years, and its advantageous application in lung parenchymal diseases and coronary artery diseases has become increasingly prominent, indicating a growing utilization in chest diseases with a promising trajectory for future development. In the future, photon-counting CT and artificial intelligence will be hot technologies that continue to develop. In essence, the evolution of dual- and multi-energy CT is anticipated to drive innovations across various domains.