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Thoracic imaging 

Thoracic imaging

Chapter:
Thoracic imaging
Author(s):

Susan J. Copley

and David M. Hansell

DOI:
10.1093/med/9780199204854.003.180302_update_001

Update:

Chest radiography—description of radiographic techniques modified to include advances in X-ray detector technology, digital tomosynthesis, and other emerging techniques.

Transthoracic ultrasonography—description of usage expanded to include detection of pneumothoraces and supraclavicular node sampling in lung cancer.

CT—description modified to include (1) dual energy CT, (2) use in screening.

MRI—description updated to include diffusion weighted MR.

Updated on 30 May 2013. The previous version of this content can be found here.
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date: 30 March 2017

Radiographic findings should always be interpreted in conjunction with the clinical picture.

Chest radiography—this remains the commonest technique in the investigation of suspected thoracic disease. Advantages are cost, availability, and a significantly lower radiation dose than CT, but even with optimal technique nearly one-third of the lungs are partially obscured by the overlying mediastinum, diaphragm, and ribs.

CT—is more sensitive and specific than chest radiography in a range of pulmonary disorders, including airways disease and diffuse interstitial lung disease. In the latter condition high-resolution CT images of the lung correlate closely with the microscopic appearances of pathological specimens and are a substantial improvement over chest radiography in terms of sensitivity, specificity and diagnostic accuracy. In many centres CT has supplanted ventilation–perfusion radionuclide imaging in the investigation of patients with suspected pulmonary embolism. Radiation dose is always a consideration in CT, particularly in children and young adults, however recent and future advances should make this less of an issue.

Ventilation/perfusion radionuclide scanning—is the commonest radionuclide study of the lungs and is most frequently used to confirm or exclude the diagnosis of suspected pulmonary embolism, but has been supplanted by CT in some centres.

Positron emission tomography (PET) and CT/PET—usually employed with the isotope 18F-fluorodeoxyglucose (FDG) for investigation and staging of lung cancer.

Transthoracic ultrasonography—the use of this technique for the imaging of lung parenchyma is limited because high-frequency sound waves do not traverse normally aerated lung, but fluid can be readily detected and the main use of ultrasound is for the localization of small or loculated pleural effusions and guiding biopsy of peripheral lung lesions and intercostal chest drain insertion.

MRI—imaging of the mediastinum by CT scanning and MRI are comparable, but MR images of the lungs are currently markedly inferior to those obtained by CT because of their very low water (and therefore proton) content. Other disadvantages are respiratory and cardiac motion artefact (unless respiratory and cardiac gating are used), relatively long scanning time, and difficulties with monitoring of critically ill patients. MRI may have a role in patients who are allergic to iodinated intravenous contrast for the evaluation of suspected pulmonary embolus or malignancies such as malignant mesothelioma. Recent advances in diffusion weighted MR imaging may be useful for evaluation of malignancy response to treatment.

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