Broncho-arterial ratio

Last revised by Dr Bruno Di Muzio on 26 Jul 2020

The broncho-arterial (BA) ratio is a descriptive parameter used in thoracic CT imaging. It is defined as the diameter of the bronchial lumen divided by the diameter of its accompanying artery 1. It is usually measured in the segmental to subsegmental artery level.

In healthy adult humans, the broncho-arterial ratio is usually taken as being around 1:1.

It can increase or decrease in various situations.

Increased broncho-arterial ratio

Some authors term an increased broncho-arterial ratio of >1.5 as bronchiectasis although several non-pathological conditions can slightly increase the ratio. These include

  • aging 2
  • high altitude 3

Pathological conditions that can increase the bronchoarterial ratio include:

Conditions that can reduce pulmonary arterial calibers

Decreased broncho-arterial ratio

Decreased broncho-arterial ratios have been described with

  • normal individual - ratios down to 0.65 have been described as acceptable within normal limits 5
  • conditions that cause bronchoconstriction

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