- Sylvia Worthy
- Senior registrar in radiology Royal Victoria Infirmary, Newcastle upon Tyne NE1 4LP
Better than chest radiography for some conditions
What you see on high resolution computed tomography of the lungs is as detailed as what you see when you look at a gross pathological specimen.1 It is the most accurate non-invasive method of evaluating lung parenchyma2 and has improved our understanding of the patterns and pathology of many pulmonary diseases.
In conventional computed tomography slices are 10 mm thick and scans are obtained at 10 mm intervals; in high resolution computed tomography slices are 1-2 mm thick and scans are obtained at 10-40 mm intervals. The images therefore represent only one tenth or less of the volume of the lung. This sampling is suited to diffuse processes affecting extensive areas of the lung but will clearly miss small lesions lying between slices. High resolution computed tomography can resolve an object of 0.5 mm diameter and is ideally suited for use in the lungs, where a high contrast between tissue and air exists.2
High resolution computed tomography comes into its own in showing the secondary pulmonary lobule, which is the site of characteristic changes in many lung diseases. Although chest radiography remains the preferred imaging technique in the assessment of patients with lung disease, two features limit its sensitivity and specificity for detecting subtle lung disease. Firstly, small differences in attenuation between normal …