Fig. 1—
Computed tomography (CT)-estimated dimensions of the airway lumen and wall, and accompanying pulmonary artery. This schematic shows the various measurements that can be made on CT images of airways and the vessels, which frequently accompany them. Linear measurements include: the airway perimeter (Pi); the long and short axes of the outer airway area (Ao) and the lumen area (Ai); wall thickness (Awt); airway lumen diameter (ALD); airway outer diameter (AoD = ALD+Awt); and arterial diameter (AD). Ratios of various linear dimensions include: ALD/AD; Awt/AD; Awt/ALD; as well as long to short axis ratios, which are a measure of the obliquity of the section. The area dimensions include: Ai; airway wall area (Aaw); outer airway area (Ao = Aaw+Ai); and arterial area (AA). Ratios of various areas include: Ai/AA; Aaw/AA; and percentage wall area (WA% = Aaw/Ao×100%). The square root of Aaw is often derived, since it is relatively linearly related to Pi. Finally, airway dimensions can be referenced to body surface area (e.g.Aaw/BSA and Awt/BSA).