Computed Tomography Imaging in ILD: New Trends for the Clinician

Today, radiological methods are an integral part of diagnostics in lung diseases, and they provide important information regarding the evaluation of interstitial lung diseases (ILDs) [...].

In recent years, a new low-dose imaging method in radiological imaging has been developed, which can investigate structural changes in the lung parenchyma in the context of a dark-field chest X-ray scan [15][16][17]. Dark-field X-ray imaging exploits the wave properties of X-rays for contrast formation by visualizing small-angle scattering occurring at air-tissue interfaces, e.g., in pulmonary alveoli [18]. High dark-field signals correlate with the number of these interfaces, e.g., alveolar walls. In these types of studies, improved visualization could be achieved compared to that obtained using conventional chest X-ray (CXR). Given the fact that conventional chest X-ray is not suitable in the early recognition or surveillance of structural lung changes, this new technique may provide a new potential in imaging the lung [19]. There have been studies in humans with emphysema showing a better correlation to the DLCO with dark-field chest X-ray than CT-based scores [18,20]. This technique enables more information to be acquired regarding the ultrastructure of the lung than through conventional chest X-ray, with only marginally more elevation exposure [18]. Hence, dark-field imaging may be a potential tool for the further quantification of lung structure changes in the future [18,[21][22][23].
In patients with various lung pathologies, by utilizing dark-field chest X-ray, these structural changes could be shown more clearly compared to conventional CXR. Compared to a CT scan, the use of dark-field chest X-ray exhibited a signal loss in the most affected areas in a patient with lymphangioleiomyomatosis, a rare disease presenting cystic changes in the lung parenchyma [23]. In a patient with combined pulmonary fibrosis and emphysema, a modulation in the dark-field chest X-ray signal according to the structural changes and their location could be shown [22]. Due to the complexity of the construction, for a long time, this technology was only feasible in the same setup as a conventional CXR and only provided two-dimensional images. The use of this novel technique is still limited to prototypes [16][17][18]20]. The limitation of the three-dimensional resolution could be overcome by the recent development of dark-field technology integration into a computed tomography scanner. It was shown that this integration significantly increased the information content in the context of parenchymal changes in the lung, as shown in small animal studies [24]. Recently, a prototype was developed that enables dark-field computed tomography scans on human-sized anthropomorphic body phantoms [25].
In the field of radiological imaging, a variety of methods have been developed in recent years. In addition to the abovementioned promising methods, much progress has been made in many areas of imaging, including MRI imaging and nuclear medicine, which offer considerable improvement in the provision of information regarding the lungs.
There is a need to integrate these new methods and their automated quantification into clinical practice. New diagnostic methods, such as dark-field imaging, may provide supplementary information in the assessment of imaging in patients with ILDs in the future.
The consistent development of thoracic imaging and its integration into everyday clinical practice is crucial, and an improvement in the care of patients with ILDs may be achieved.
Funding: This research received no external funding.

Conflicts of Interest:
The author declares no conflict of interest.

Abbreviations
CALIPER Computer-Aided Lung Informatics for Pathology Evaluation and Rating CT computed tomography CXR chest X-ray DLCO diffusion capacity of the lung for carbon monoxide uptake ILD interstitial lung disease