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THE BASIC PRINCIPLES OF HRCT OF THE THORAX

“ Why? HRCT of the chest is the  only  way to demonstrate the secondary pulmonary lobule (i.e. the basic anatomical structure responsible fo...

Why?

HRCT of the chest is the only way to demonstrate the secondary pulmonary lobule (i.e. the basic anatomical structure responsible for gas exchange composed of acini, bronchioles, lymphatics and vessels).
When?
Any diffuse lung disease including interstitial lung disease, pulmonary eosinophilias and obstructive lung disease and to investigate patients with symptoms and a normal chest x-ray.
How?
The key aspects of HRCT are thin collimation (1-2-mm slices) and high spatial resolution reconstruction. Slices may be taken at staggered intervals (‘interspaced’; e.g. six to eight images total) or as a volumetric dataset (e.g. every 10 mm)—the merits of each are debatable. Patients are usually scanned supine; prone positioning is useful to differentiate disease from ‘dependent’ changes (i.e. atelectasis in older patients and smokers). Images are usually gathered in full inspiration. Expiratory scans are used to demonstrate air-trapping or to differentiate between vascular and airway disease as a cause of airtrapping.