Report from RSNA: CTA nails down role of gold standard for pulmonary embolism

Whether it scans in four slices or 16, CT is the method of choice for detecting pulmonary emboli, researchers said at the RSNA meeting. Even four-slice technology boasts a negative predictive value greater than 99%, better than ventilation/perfusion (V/Q) studies or conventional pulmonary angiography.

Differences among four-, eight-, and 16-slice scanners appear marginal so far, but few data are available to solidify any claims of superiority for 16, except in speed. Researchers at Stanford University clocked lung scan times at 26.6 seconds for four-slice, 9.25 seconds for eight-slice, and 5.45 seconds for 16.

Dr. Alessandro Napoli and colleagues at Stanford reviewed CT studies for 1240 consecutive patients referred for suspected pulmonary emboli. Overall, 20% of cases were deemed positive, with 41% of emboli found in the segmental arteries, 27% in lobal regions, 17% in subsegmental arteries, and 15% on the main branches.

While there was no statistically significant difference in detection rates among the three generations of scanners, readers said that eight- and 16-slice studies yielded more and clearer diagnostic data. The 16-slice scanner may eventually prove better at finding subsegmental emboli, but only a small number of cases were included in the study.

If a CT study is negative, it is safe to forgo further examination. Researchers at the University of South Carolina conducted a metastudy of 14 published papers with 3283 patients who had undergone CTA to evaluate suspected pulmonary emboli, had negative findings, and had stopped anticoagulation therapy based on those findings. Fourteen developed fatal pulmonary embolism, 23 demonstrated nonfatal embolism, and 52 showed evidence of deep venous thrombosis during follow-up.

The studies produced 95% to 100% negative predictive value (NPV), with an average of 99.1%. NPV for mortality was 99.4%. Whether the CTAs were performed on single-slice or multislice CT made no significant difference. By comparison, conventional pulmonary angiography has an NPV of 98.4%, and V/Q studies average 88%.