CLINICAL INVESTIGATIONS Technegas Versus 81mKr Ventilation–Perfusion Scintigraphy: A Comparative Study in Patients with Suspected Acute Pulmonary Embolism

81mKr is widely used as a ventilation agent to diagnose pulmonary embolism (PE). However, 81mKr is expensive, which limits its continuous availability. Technegas can be an alternative ventilation agent with the advantage of being less expensive and available daily. The aim of this study was to compare the value of technegas with that of 81mKr in the detection of PE. Methods: Ninety-two consecutive patients (29 men; mean 6 SD, 53 6 17 y old) with at least one segmental perfusion defect (Hull criteria) were studied prospectively. Perfusion and ventilation (V/Q) lung scintigraphy with both technegas and 81mKr were performed within 24 h on all patients. V/Q lung scan results were classified as high probability for PE (normal ventilation study) or nondiagnostic (abnormal ventilation study). All V/Q lung scans were read by two experienced nuclear physicians in consensus. For the intraand interobserver variabilities, two experienced observers independently read the V/Q lung scans. Results: 81mKr and technegas showed a good agreement (k, 0.68; 95% confidence interval [CI], 0.53–0.82). However, technegas significantly increased the number of nondiagnostic V/Q lung scans (P 5 0.035). In 15 patients, a discrepancy was found between 81mKr and technegas. False-positive V/Q lung scan results occurred in 4 of 12 patients (33%) with 81mKr and in 2 of 3 patients (66%) with technegas. The intraand interobserver variabilities were 0.71–0.88 (95% CI, 0.56–1.0) for perfusion/81mKr and 0.74–0.96 (95% CI, 0.58–1.0) for perfusion/technegas. Conclusion: In comparison with 81mKr, technegas does not result in more false-positive V/Q lung scan results. The use of technegas, however, increases the number of nondiagnostic V/Q lung scan results, which would increase the demand for further additional testing to confirm or refute PE.