Computed tomography and the lung: review of anatomic and densitometric features with their clinical application.

The lung scan findings in 22 normal patients (9 men, 13 women; mean age 39.3 years) obtained using a GE CT/T 8800 scanner have been analyzed. Central arteries and veins can be distinguished on the unenhanced scan by following their course from the hilum on sequential scans, by identifying their relationship to bronchi, or by their vertical or horizontal orientation in the upper and lower lobes. However, arteries cannot be distinguished from veins in the lung periphery. The center of the lung (medulla) harbors "trunk" arteries, veins, bronchi and an alveolar meshwork while the periphery (cortex) is characterized by small vessels (1-3 mm) perpendicularly oriented to the pleural surface. Attenuation densities from the right lung at the aortic arch, carina and above the right hemidiaphragm were obtained followed by systematic analysis of various parameters including the mean anterior and posterior cortical and medullary attenuation density, anterior and posterior mean lung density, total mean lung density for each slice and the entire right lung, and the anteroposterior gradients. Different attenuation densities and gradients will be obtained using other models of scanners. The evidence suggests that the medulla is a "reservoir" zone, capable of accommodating increased blood flow under appropriate conditions. Clinical application of these parameters to the diagnosis of diffuse lung disease is illustrated.