HRCT chest: expiratory images

Expiratory high-resolution CT (HRCT) imaging corresponds to an additional CT acquisition performed as part of the HRCT chest protocol. It represents a scan performed with the patient on supine and images obtained at the end expiration. 

It is a useful method for detecting small airways obstructive lung disease, in which the air remains trapped in the pulmonary lobules even after the expiration (air-trapping). This technique may also be applied in the assessment for tracheobronchomalacia, although a dedicated protocol with small ROI focused in the central airways is preferred.  

Ideally, an expiratory HRCT scan should be performed in all obstructive airway diseases. Some institutions make it routinely acquired in every initial HRCT assessment. 

Common indications include:

  • expiration: the patient should be taught, also practice before, how to perform and hold a full expiration for a few seconds
  • sequential spaced is prefered over a volumetric acquisition in view of a reduction in the radiation dose the patient is exposed
  • gap of 2-4 cm between the two sets of images
  • no intravenous contrast is required
  • postprocessing: high-spatial-frequency or sharpening algorithm (bone algorithm)
  • expected findings in expiration include:
    • diffuse increase in lung attenuation
    • decrease in the cross-sectional lung area
    • reduction in the caliber of the airways
      • the trachea is usually taken as a reference to assess technique adequacy: it should change from a round/elliptical shape on inspiration to a crescent shape on expiration, with bowing of its posterior membranaceous wall
  • air-trapping: pulmonary lobules with less than normal increase in attenuation and lack of volume reduction
  • obliteration of the tracheal or main bronchi lumen on expiration is indicative of tracheobronchomalacia 
CT examinations
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Article information

rID: 28654
System: Chest
Section: Approach
Tag: pm, refs
Synonyms or Alternate Spellings:
  • Expiratory high resolution CT
  • Expiratory HRCT scan

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