CO2-enhanced CT imaging for the detection of pulmonary emboli: Feasibility study in a porcine model

Abstract Rationale and Objectives The authors investigated the feasibility of using computed tomography (CT) with CO 2 gas as a negative contrast agent for detecting pulmonary emboli in a porcine model. Materials and 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 CO 2 (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 CO 2 . The CO 2 volumes and scan delays were qualitatively assessed. The supine and prone CT scans and the number and location of thrombi depicted in the CO 2 - 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 CO 2 enhancement. An infusion of 120 mL of CO 2 was sufficient to enhance the entire pulmonary artery, and scanning timed to coincide with the completion of infusion was the most effective. Both the CO 2 - and con-trast-enhanced CT scans demonstrated all thrombi. Thrombi were more apparent on the CO 2 -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 CO 2 -enhanced scanning and could not be resuscitated. The cause of these events was not determined in the current study. Conclusion The CT depiction of pulmonary emboli is feasible with CO 2 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 CO 2 gas for this application.