The advantage of digital tomosynthesis for pulmonary nodule detection concerning influence of nodule location and size: a phantom study
Introduction
Chest radiography (CXR) is a basic technique for the investigation of pulmonary disease and is frequently used because of its economical merit and accessibility. Several studies have reported that the accepted error rate for the detection of lung cancer ranged from 10 to 50%, and there has been insufficient improvement over the past decades.1 Various obstacles influence the ability for detection of nodules in chest radiography. Above all, contrast difference between the nodule and surrounding area affects the rate of nodule detection: a poorly penetrated area of the lung (subpleural, retrodiaphragmatic, retrocardiac, and paramediastinal), superimposed structures, and complexity of the area could have a major impact on nodule detection.2, 3, 4, 5 As a result, nodule location and the anatomical background have been identified as major contributing factors for the detection of nodules.
Two representative technical developments in projection radiography for evaluating pulmonary nodules are digital tomosynthesis (DTS) and dual-energy subtraction (DES). The DES technique, which can remove overlying bone structures to create soft-tissue selective images, has emerged to enhance the visualisation of pulmonary nodules; however, reliable results have been confined only to nodules overlapping with rib or clavicle and it could not reduce the visual clutter from the overlying soft tissue.6 DTS provides an arbitrary number of image planes throughout the entire chest by reconstruction of a set of projection radiographs at different angles during a limited range of X-ray tube movement. This technique enables improvement of nodule detection by eliminating the visual clutter of overlying anatomy and providing depth localisation.7, 8 Therefore, DTS could allow the observer to detect pulmonary nodules more accurately than CXR and DES by removing the effect of anatomical location; however, there are few studies evaluating the diagnostic performance of DTS to detect pulmonary nodules regarding location.9, 10, 11
The hypothesis of the present study was that DTS outperforms CXR and DES to detect pulmonary nodules located in danger zones than in non-danger zones. Therefore, the purpose of the present study was to investigate the advantages of DTS compared to CXR and DES for the detection of solid simulated pulmonary nodules (SPNs) especially focusing on the influence of nodule location and size.
Section snippets
Materials and methods
A total of 192 sets of examinations (each set comprised of three examination techniques; CXR, DES, and DTS) were prepared. Half (96/192) of the examinations contained SPNs (from 1 to 4) and the other half of the examinations were nodule-free.
Overall diagnostic performance of each technique for detection of SPN
The JAFROC curves and figure of merit (FOM) for each technique by individual observers are shown in Table 1. The observer-averaged FOM from the JAFROC analysis was 0.78 (95% confidence interval [CI]: 0.72–0.83) for CXR, 0.77 (95% CI: 0.71–0.84) for DES, and 0.95 (95% CI: 0.93–0.97) for DTS regardless of SPN location and size. The performance of SPN detection between CXR and DES was not significantly different (p=0.878); however, DTS showed significantly better performance than CXR and DES for
Discussion
Although DTS has some limitations including weakness for motion artefact and subpleural lesions, usefulness of DTS has increased due to its ability of obtaining increased diagnostic information by volumetric imaging with a radiation dose comparable to that of conventional chest radiography.8, 17 Previous studies have reported many potential roles of DTS for superior performance of pulmonary nodules detection than CXR,18, 19, 20 pulmonary mycobacterial disease,21 detection of lung metastasis,22,
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