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Modalities in Evaluation of Chest Diseases

Routine Radiography Routine chest radiography, generally including both posteroanterior and lateral views, is an integral part of the diagnostic evaluation of diseases involving the pulmonary parenchyma, the pleura, and, to a lesser extent, the airways and the mediastinum
CT offers several advantages over routine chest radiography.
  1. Cross-sectional images allows distinction between densities that would be superimposed on plain radiographs.
  2. Better in characterizing tissue density, distinguishing subtle density differences be- tween adjacent structures, and providing accurate size assessment of lesions.
    As a result, CT is particularly valuable in assessing hilar and mediastinal disease (which is often poorly characterized by plain radiography), in identifying and characterizing disease adjacent to the chest wall or spine (including pleural disease), and in identifying areas of fat density or calcification in pulmonary nodules.
  3. Its utility in the assessment of mediastinal disease has made CT an important tool in the staging of lung cancer.
  4. With CT angiography, in which IV contrast is administered and images are acquired rapidly by helical scanning, pulmonary emboli can be detected in segmental and larger pulmonary arteries.
  5. With high-resolution CT (HRCT), the thickness of individual cross-sectional images is ~1–2 mm, rather than the usual 7–10 mm, and the images are reconstructed using high spatial resolution algorithms. The visible detail on HRCT scans allows better recognition of subtle parenchymal and airway disease, such as bronchiectasis, emphysema, and diffuse parenchymal disease
MRI The role of MR imaging in the evaluation of respiratory system disease is less well defined than that of CT. Because MR generally provides a less detailed view of the pulmonary parenchyma as well as poorer spatial resolution, its usefulness in the evaluation of parenchymal lung disease is limited at present. However, MR images can be reconstructed in sagittal and coronal as well as trans- verse planes, so that the technique is well suited for imaging abnormalities near the lung apex, the spine, and the thoracoabdominal junction.
Bronchoscopy  Although bronchoscopy is now performed almost exclusively with flexible fiberoptic instruments, rigid bronchoscopy, generally performed in an operating room on a patient under general anesthesia, still has a role in selected circumstances, primarily because of a larger suction channel and the fact that the patient can be ventilated through the bronchoscope channel. These situations include the retrieval of a foreign body and the suctioning of a massive hemorrhage, for which the small suction channel of the bronchoscope may be insufficient.
Scintigraphic Imaging Radioactive isotopes, administered by either IV or inhaled routes, allow the lungs to be imaged with a gamma camera. In the past, scintigraphic imaging in the form of ventilation-perfusion lung scanning was commonly performed for evaluation of pulmonary embolism. However, with advances in CT scanning, scintigraphic imaging has largely been replaced by CT angiography in patients with suspected pulmonary embolism.
PET scan Used in the evaluation of solitary pulmonary nodules and as an aid to staging lung cancer through identification of mediastinal lymph node involvement by malignancy.
Pulmonary Angiography Gold standard for pulmonary embolism.
Other, less common indications for pulmonary angiography include visualization of a suspected pulmonary arteriovenous malformation and assessment of pulmonary arterial invasion by a neoplasm. However, with advances in CT scanning, traditional pulmonary angiography has largely been re- placed by CT angiography.

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