title: Air trapping on CT of patients with pulmonary embolism.
abstract: OBJECTIVE
  We evaluated the relationship of air trapping to mosaic perfusion in patients with pulmonary embolism.
  
  
  METHODS
  Forty-one consecutive patients with suspected pulmonary embolism underwent expiratory CT followed by helical CT angiography. After excluding 12 patients who had airway disease or were smokers, we divided the patients into two groups: those with (n = 15) and without (n = 14) pulmonary embolism. For each patient, six expiratory images were evaluated for the presence of air trapping, and the corresponding six images from CT angiography were evaluated for the presence of mosaic perfusion. Clot locations were assessed on CT angiography and were correlated with the presence of air trapping and mosaic perfusion.
  
  
  RESULTS
  In patients with pulmonary embolism, mosaic perfusion was identified in 32 areas (seven patients, 46.7%), and air trapping was identified 68 areas (nine patients, 60%). Of the 32 areas of mosaic perfusion, 23 areas (71.9%) showed air trapping on expiratory CT scans. Of the 68 areas with air trapping on expiratory scans, 23 areas (33.8%) showed mosaic perfusion on inspiratory scans, and 44 areas (64.7%) had clots in the arteries leading to them. Clots were more frequently identified in areas of lower attenuation on inspiratory CT scans and air trapping (21/23) than in those of normal attenuation on inspiratory CT scans and air trapping (23/45) (p < 0.005). Only one patient without pulmonary embolism had air trapping (p < 0.005).
  
  
  CONCLUSIONS
  Air trapping is common in pulmonary embolism and may be the cause of mosaic perfusion. Air trapping can be seen distal to vessels not showing pulmonary embolism.
authors.affiliation: Department of Radiology, St. Marianna University School of Medicine, 2-16-1 Sugao, Miyamae-Ku, Kawasaki City, 216-8511 Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Arakawa
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Kurihara
authors.forename: Kaoru
authors.initials: K
authors.lastname: Sasaka
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Nakajima
authors.forename: W Richard
authors.initials: WR
authors.lastname: Webb
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000792:Angiography; D004618:Embolism, Air / Q000150:complications* / Q000000981:diagnostic imaging* / Q000503:physiopathology; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D011651:Pulmonary Artery / Q000000981:diagnostic imaging / Q000503:physiopathology; D011652:Pulmonary Circulation / Q000502:physiology; D011655:Pulmonary Embolism / Q000150:complications* / Q000000981:diagnostic imaging* / Q000503:physiopathology; D012115:Residual Volume / Q000502:physiology; D014057:Tomography, X-Ray Computed