Diagnostic modalities for assessing respiratory diseases include imaging studies and techniques for acquiring biological specimens.
The chest x-ray (CXR), generally including both posteroanterior and lateral views, is often the first diagnostic study in pts presenting with respiratory symptoms. With some exceptions (e.g., pneumothorax), the CXR pattern is usually not sufficiently specific to establish a diagnosis; instead, the CXR serves to detect disease, assess magnitude, and guide further diagnostic investigation. With diffuse lung disease, CXR can detect an alveolar, interstitial, or nodular pattern. CXR can also detect pleural effusion and pneumothorax, as well as abnormalities in the hila and mediastinum. Lateral decubitus views can be used to estimate the size of freely flowing pleural effusions.
Chest computed tomography (CT), typically performed with helical scanning and multiple detectors, is widely used to clarify radiographic abnormalities detected by CXR. Advantages of chest CT compared with CXR include (1) ability to distinguish superimposed structures due to cross-sectional imaging; (2) superior assessment of tissue density, permitting accurate assessment of the size and density of pulmonary nodules and improved identification of abnormalities adjacent to the chest wall, such as pleural disease; (3) with the use of IV contrast, ability to distinguish vascular from nonvascular structures, which is especially useful in assessing hilar and mediastinal abnormalities (including staging of lung cancer); (4) with CT angiography, ability to detect pulmonary emboli; and (5) due to superior visible detail, improved recognition of parenchymal and airway diseases, including emphysema, bronchiectasis, lymphangitic carcinoma, and interstitial lung disease. In the appropriate clinical context, idiopathic pulmonary fibrosis can be reliably diagnosed based on chest CT. Low dose chest CT is recommended for lung cancer screening among pts aged 55–80 with at least a 30 pack-year smoking history, who have smoked in the past 15 years. With appropriate data reanalysis, chest CT scans can provide a three-dimensional reconstruction of the airways down to at least the sixth generation, providing a virtual bronchoscopy. Virtual bronchoscopies may be helpful in assessing stenotic airways and in planning therapeutic bronchoscopy procedures.
Diagnostic US is not useful for assessing the pulmonary parenchyma, but it can detect and localize pleural abnormalities and guide thoracentesis of a pleural effusion. As a nonionizing imaging approach, it is safe to perform on pregnant women and children. Real-time US imaging can assess diaphragmatic mobility. Portable US is useful to monitor resolution of pneumothorax and pleural effusion.
Ventilation-perfusion lung scans can be used to assess for pulmonary thromboembolism but have largely been replaced by CT angiography. Positron emission tomographic (PET) scanning assesses the uptake and metabolism of a radiolabeled glucose analogue. Because malignant lesions usually have increased metabolic activity, PET scanning, especially when combined with CT images in PET/CT, is useful to assess pulmonary nodules ...