title: CO2-enhanced CT imaging for the detection of pulmonary emboli: feasibility study in a porcine model.
abstract: OBJECTIVE
  The authors investigated the feasibility of using computed tomography (CT) with CO2 gas as a negative contrast agent for detecting pulmonary emboli in a porcine model.
  
  
  METHODS
  Seven pigs with or without pulmonary emboli underwent thoracic imaging with multi-detector row spiral CT. To identify optimal injection and scanning protocols, the first four pigs were scanned repeatedly in the supine and prone positions with different scan delays (10, 15, and 20 seconds) and different volumes of CO2 (60, 120, 180, and 240 mL), which were hand infused (each infusion took 10-15 seconds). The last five pigs with emboli were scanned with iodinated contrast medium and then rescanned with 120 or 180 mL of CO2. The CO2 volumes and scan delays were qualitatively assessed. The supine and prone CT scans and the number and location of thrombi depicted in the CO2- and contrast material-enhanced CT scans were compared.
  
  
  RESULTS
  Because the pulmonary artery in pigs is in the posterior anatomy, the prone position was more effective than the supine position with CO2 enhancement. An infusion of 120 mL of CO2 was sufficient to enhance the entire pulmonary artery, and scanning timed to coincide with the completion of infusion was the most effective. Both the CO2- and contrast-enhanced CT scans demonstrated all thrombi. Thrombi were more apparent on the CO2-enhanced CT scans than on the contrast-enhanced scans because of the high contrast interface between soft tissue and gas. However, two of the seven pigs with thrombi experienced abrupt cardiac arrest after CO2-enhanced scanning and could not be resuscitated. The cause of these events was not determined in the current study.
  
  
  CONCLUSIONS
  The CT depiction of pulmonary emboli is feasible with CO2 gas as a negative contrast agent and may even be superior to that with iodinated contrast media. Further studies are required to evaluate the safety of this method and to develop an improved delivery of CO2 gas for this application.
authors.affiliation: Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 S Kingshighway Blvd, St Louis, MO 63110, USA.
authors.forename: Kyongtae T
authors.initials: KT
authors.lastname: Bae
authors.forename: Cheng
authors.initials: C
authors.lastname: Hong
authors.forename: Christoph R
authors.initials: CR
authors.lastname: Becker
authors.forename: Srini
authors.initials: S
authors.lastname: Prasad
authors.forename: Mark A
authors.initials: MA
authors.lastname: Nolte
authors.forename: Paul E
authors.initials: PE
authors.lastname: Eisenbeis
authors.forename: Jay P
authors.initials: JP
authors.lastname: Heiken
mesh_terms: D000818:Animals; D002245:Carbon Dioxide; D003287:Contrast Media; D003937:Diagnosis, Differential; D004195:Disease Models, Animal; D005240:Feasibility Studies; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging*; D013552:Swine; D036542:Tomography, Spiral Computed
chemical_list: D003287:Contrast Media; D002245:Carbon Dioxide