title: Use of expiratory CT pulmonary angiography to reduce inspiration and breath-hold associated artefact: contrast dynamics and implications for scan protocol.
abstract: OBJECTIVE
  To investigate the effects of scanning in expiration during computed tomography pulmonary angiography (CTPA).
  
  
  METHODS
  One hundred and eighty-one consecutive expiratory CTPA examinations were compared with 145 inspiratory CTPA examinations performed using a standardized protocol through assessment of attenuation seen in the cardiac chambers, pulmonary artery (PA), and ascending aorta.
  
  
  RESULTS
  Expiratory scans showed greater attenuation at the pulmonary trunk, right PA, left PA, lobar and segmental PAs (p<0.05). Expiratory scans showed a lower incidence of transient contrast medium interruption (p<0.001) and generalized unsatisfactory PA opacification (p<0.05). Scans with generalized low PA attenuation had lower attenuation in the right ventricle, left heart, and ascending aorta (p<0.001) suggesting that contrast medium delivery or dilution prior to contrast medium entry into the PA is responsible. Expiratory scans showed lower quality scores (p<0.001) for depiction of lung parenchyma.
  
  
  CONCLUSIONS
  Expiratory scanning could be used as an optimal protocol for dedicated PA imaging. However, it suffers from inferior parenchymal imaging and should probably be reserved for failed inspiratory breath-hold CTPA.
authors: Department of Radiology, Bristol Royal Infirmary, Bristol, UK. alex_mortimer@hotmail.com
authors: A M
authors: AM
authors: Mortimer
authors: R K
authors: RK
authors: Singh
authors: J
authors: J
authors: Hughes
authors: R
authors: R
authors: Greenwood
authors: M C K
authors: MC
authors: Hamilton
mesh_terms: D000792:Angiography / Q000379:methods*; D016477:Artifacts; D045853:Exhalation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011651:Pulmonary Artery / Q000000981:diagnostic imaging* / Q000503:physiopathology; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging* / Q000503:physiopathology; D011856:Radiographic Image Enhancement / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D014682:Vena Cava, Inferior / Q000000981:diagnostic imaging* / Q000503:physiopathology; D014683:Vena Cava, Superior / Q000000981:diagnostic imaging* / Q000503:physiopathology