Pulmonary Embolism

Rationale and Objectives The purpose of this study was to compare gadolinium-enhanced magnetic resonance (MR) angiography with contrast material–enhanced computed tomography (CT) for the detection of small (4–5-mm) pulmonary emboli (PE), with a methacrylate cast of the porcine pulmonary vasculature used as the diagnostic standard. Materials and Methods In 15 anesthetized juvenile pigs, colored methacrylate beads (5.2 and 3.8 mm diameter—the size of segmental and subsegmental emboli in humans) were injected via the left external jugular vein. After embolization, MR angiographic and CT images were obtained. The pigs were killed, and the pulmonary arterial tree was cast in clear methacrylate, allowing direct visualization of emboli. Three readers reviewed CT and MR angiographic images independently and in random order. Results Forty-nine separate embolic sites were included in the statistical analysis. The mean sensitivity (and 95% confidence intervals) for CT and MR angiography, respectively, were 76% (68%–82%) and 82% (75%–88%) (P > .05); the mean positive predictive values, 92% (85%–96%) and 94% (88%–97%) (P > .05). In this porcine model, PE were usually seen as parenchymal perfusion defects (98%) with MR angiography and as occlusive emboli (100%) with CT. Conclusion MR angiography is as sensitive as CT for the detection of small PE in a porcine model.