Chest radiography (X-ray) is an essential part of the diagnostic (and monitoring) examination, and is the first step in the radiological evaluation of patients with suspected respiratory diseases. Modern digital radiography offers a high image quality and the potential for reduction of the radiation dose.
Computed tomography (CT) of the chest is the second most important radiological modality in respiratory medicine, allowing much more detailed visualisation of thoracic structures than radiography. It is often performed with intravenous contrast enhancement (in suspected pulmonary embolism cases, for example). CT is also helpful for guiding needle aspiration of peripheral lung lesions. High-resolution CT (HRCT) has improved the diagnosis of diffuse interstitial lung disease considerably. Low-dose CT is used in follow-up and serial early lung cancer detection. CT can be used for virtual bronchoscopy or angiography, but this has not become routine. CT is applied in combination with positron emission tomography (PET) mainly for staging lung cancer and other malignancies, and in the differential diagnosis between benign and malignant lung lesions (figure 2). CT/HRCT has almost wholly replaced bronchography for the diagnosis of bronchiectasis.
Pulmonary and bronchial angiography
Pulmonary angiography and bronchial angiography (together with bronchial artery embolisation for the treatment of haemoptysis) are invasive techniques for imaging vessels and are only used if less invasive techniques (contrast CT/magnetic resonance imaging (MRI)) fail or need to be confirmed.
Fluoroscopy (an X-ray technique by which respiratory movement is visualised directly) is used mainly for guidance of biopsy of peripheral lung lesions and for differential diagnosis of an elevated diaphragm.
Magnetic resonance imaging
MRI has the advantage that radiation is avoided. Its main indications are visualisation of the great vessels and the heart, but it is also useful with suspected tumour invasion of the mediastinum and the chest wall.
Ultrasonography has become an important imaging technique. Its advantages are lack of radiation, low cost and mobility. It is mainly used in the investigation of pleural effusions (in which it also has a role in guiding thoracentesis) but also in pleural thickening, chest wall abnormalities, for the diagnosis of pneumothorax and for biopsies of lesions adjacent to the chest wall. A special application is endobronchial ultrasound (EBUS), which can be used for visualisation of mediastinal lymph nodes as well as pulmonary parenchymal lesions. Its most important use is the sampling of mediastinal lymph nodes in the setting of endoscopic lung cancer staging, where EBUS has largely replaced mediastinoscopy. Echocardiography allows noninvasive screening for pulmonary hypertension, although right heart catheterisation may be needed for the final diagnosis.
Nuclear medicine techniques
Nuclear medicine techniques include perfusion and ventilation scintigraphy, which are mainly indicated in the diagnosis of pulmonary embolism (figure 3) but also for regional lung function studies, e.g. for predicting post-operative lung function before lung surgery. Inhalation scintigraphy can be used to investigate mucociliary clearance.