The initial imaging tool for the lung parenchyma remains the chest radiograph. It is unsurpassed in the amount of information it yields in relation to its cost, radiation dose, availability, and ease of performance. However, the chest radiograph has its limitations. It is normal in 10 to 15 percent of symptomatic patients with proven infiltrative lung disease, up to 30 percent of those with bronchiectasis, and close to 60 percent of patients with emphysema . In several studies, the chest radiograph has been shown to have an overall sensitivity of 80 percent and a specificity of 82 percent for detection of diffuse lung disease . Chest radiography could provide a confident diagnosis in only 23 percent of cases, and those confident diagnoses proved correct only in 77 percent of cases.
For these reasons, high resolution computed tomography (HRCT, also called thin-section CT scanning), is frequently used to help clarify specific problems. The clinical applications of HRCT will be reviewed here. The principles of CT imaging are discussed separately. (See "Principles of computed tomography of the chest".)
CLINICAL APPLICATION OF HRCT
HRCT, which has a sensitivity of 95 percent and a specificity approaching 100 percent [2-5], can often provide more information than either chest radiography or conventional CT scanning. A confident diagnosis is possible in roughly one-half of cases, and these are proven correct an estimated 93 percent of the time.
HRCT may be particularly useful in the following settings:
- It can detect lung disease in symptomatic patients with a normal chest radiograph.
- It can provide an accurate assessment of the pattern, distribution, and to a lesser degree, assess the activity and potential reversibility of diffuse lung disease.
- It demonstrates a high correlation between radiographic and histopathologic appearances.
- In patients with nondiagnostic findings on chest radiography, it can provide a more specific diagnosis or exclude certain diseases.
- It can be used to determine the type and site of lung biopsy. (See "Role of lung biopsy in the diagnosis of interstitial lung disease".)
- It can be used to detect or evaluate specific problems or diagnoses, such as metastatic lesions, solitary pulmonary nodules, emphysema, bullous lung disease, bronchiectasis, and diffuse parenchymal disease.