Mosaic perfusion

Patchy dark areas of lucent lung which are poorly perfused

• Small vessel disease (5%) - chonic PE
• Small airway disease (95%)-
  • Bronchiolitis obliterans, asthma, hypersensitivity pneumonitis, cystic fibrosis
  • Cause secondary decreased perfusion

Separate from Air Trapping on expiratory HRCT will give a similar appearance, but differential includes small airway disease, not small vessel disease, because presumably not present on inhalation