The next step in lung ultrasonography: From two-dimensional to three-dimensional ultrasonography

Dear Editor, Ultrasonography (US) systems, first discovered in the 1920s, began to be used in the field of medicine in the 1940s. US operates by transmitting sound waves beyond the audible range of the human ear into tissues via a probe and converting the reflected echoes into images using a monitor. Due to this working principle, early applications of the US primarily focussed on solid organs. Since the lungs are air-filled organs in healthy individuals, their ability to reflect ultrasound waves is considerably limited. As a result, the use of the US in lung imaging was delayed. However, in current practice, thoracic ultrasonography (TUS) is effectively used in the diagnosis of various pulmonary conditions, especially pleural effusions, as well as soft tissue tumours of the lung that are firmly adhered to the chest wall without interposing air.[1] Until the early 1970s, lung imaging was limited to X-ray techniques; the invention of computed tomography (CT) revolutionised diagnostic radiology by providing three-dimensional visualisation of anatomical structures. Similarly, three-dimensional ultrasonography (3D-US) is playing an increasingly significant role in US-based diagnostic procedures, particularly in cardiology, gynecology, and urology. Today, conventional two-dimensional (2D) US platforms are considered standard imaging modalities, providing sectional images in a single plane (e.g., sagittal or transverse) using linear or convex probes. In contrast, 3D-US systems combine multiple 2D images acquired from various angles to generate volumetric data, which can then be processed using software algorithms to create three-dimensional reconstructions (volumetric modelling). This advancement allows for more accurate assessment of anatomical and pathological structures, as well as the measurement of organ volumes (e.g., tumour volume, effusion volume).[2] While advancements in 2D-US continue within the field of pulmonology, the imaging potential offered by 3D-US should not be overlooked. 3D-US devices are capable of producing near-real-time images with a high degree of spatial accuracy. One of their major advantages over 2D-US systems is the added depth dimension, which allows volumetric structures to be visualised more realistically.[3] A review of the English-language literature reveals that studies specifically addressing the use of 3D-US in pulmonology are virtually non-existent. While healthy, air-filled lungs yield limited information when assessed via US, this limitation does not apply to the pleura, which can be reliably visualised in nearly all cases. Therefore, we believe that 3D-US may be particularly useful in the assessment of pleural structures. Moreover, its ability to display images in multiple planes, offer different viewing angles through software algorithms (e.g., top-down views of the pleura), and create an unlimited number of slices represents a breakthrough in imaging [Figure 1].Figure 1: Simultaneous 2D-US and 3D-US images obtained from the same monitor in different planes (transverse and sagittal) of a case with pleural effusion. (a) The thickened visceral pleura located just above the lung parenchyma is indicated by the red arrow. (b) In a case where pleural effusion was detected with 2D-US, the 3D-US system provides depth perception of the effusion. (c) While only the pleural effusion is visualised with 2D-US, 3D-US enables a top-down view of the pleura through software algorithms. (d) While 2D-US visualises only the pleural effusion and pleural thickening, 3D-US creates depth perception and more clearly delineates irregular and thickened pleural surface areas, marked with small red arrowsSimilarly, peripheral lung tumours that are in direct contact with the chest wall (without interposing air) can also be readily visualised using 3D-US, and the same advantageous perspectives mentioned above can be applied [Figure 2].[4-5]Figure 2: Simultaneous 2D-US and 3D-US images obtained from the same monitor in different planes (transverse and sagittal) of a case with a pulmonary mass and a metastatic chest wall lesion. (a) A mass lesion visualised in a single plane by 2D-US is shown in 3D-US images from three different angles and planes. The relationship of the mass with surrounding tissues and its internal structure appear more clearly and closely resemble its actual anatomical configuration. (b) Simultaneous 2D-US and 3D-US images of a soft tissue mass in the lung parenchyma that is adherent to the chest wall. Using 3D-US software, the lesion can be reconstructed in multiple planes and cross-sections as desired. (c) In a patient with a pleura-based mass, 3D-US allows imaging from alternative perspectives, revealing the lesion’s surface and clearly visualising its irregular marginsIn conclusion, it should be kept in mind that 3D-US may have a valuable role in the diagnosis of pulmonary diseases within the field of pulmonology. We believe it is essential to begin conducting research on this topic now in order to keep pace with and be prepared for the rapid developments in ultrasound technology. Author contributions Conceptualization; Coşkun DOĞAN, Göksel Menek Data curation; Coşkun DOĞAN, Göksel Menek Formal analysis; Coşkun DOĞAN, Göksel Menek Funding acquisition; Coşkun DOĞAN, Göksel Menek Investigation; Coşkun DOĞAN, Göksel Menek Methodology; Coşkun DOĞAN, Göksel Menek Project administration; Coşkun DOĞAN, Göksel Menek Resources; Coşkun DOĞAN Software; Coşkun DOĞAN, Göksel Menek Supervision; Coşkun DOĞAN, Göksel Menek Validation; Coşkun DOĞAN, Göksel Menek Visualization; Coşkun DOĞAN, Göksel Menek Roles/Writing - original draft; and Writing - review and editing: Coşkun DOĞAN Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.