• Kyongtae T Bae, Cheng Hong, Christoph R Becker, Srini Prasad, Mark A Nolte, Paul E Eisenbeis, and Jay P Heiken.
• Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 S Kingshighway Blvd, St Louis, MO 63110, USA.
• Acad Radiol. 2003 Mar 1; 10 (3): 313-20.

Rationale And ObjectivesThe 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.Materials And MethodsSeven 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.ResultsBecause 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.ConclusionThe 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.

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