Technegas versus Kr-81m ventilation-perfusion scintigraphy: A comparative study in patients with suspected acute pulmonary embolism

Kr-81m is widely used as a ventilation agent to diagnose pulmonary embolism (PE). However, Kr-81m is expensive, which limits its continuous availabili ty. Technegas can be an alternative ventilation agent with the advantage of being less expensive and available daily. The aim of this study was to com pare the value of technegas with that of Kr-81m in the detection of PE. Met hods: Ninety-two consecutive patients (29 men; mean +/- SD, 53 +/- 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 Kr-81m 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 w ere read by two experienced nuclear physicians in consensus. For the intra- and interobserver variabilities, two experienced observers independently r ead the V/Q lung scans. Results: Kr-81m and technegas showed a good agreeme nt (kappa, 0.68; 95% confidence interval [CI], 0.53-0.82). However, techneg as significantly increased the number of nondiagnostic V/Q lung scans (P = 0.035). In 15 patients, a discrepancy was found between Kr-81m and technega s. False-positive V/Q lung scan results occurred in 4 of 12 patients (33%) with Kr-81m and in 2 of 3 patients (66%) with technegas. The intra- and int erobserver variabilities were 0.71-0.88 (95% Ci, 0.56-1.0) for perfusion/Kr -81m and 0.74-0.96 (95% CI, 0.58-1.0) for perfusion/technegas. Conclusion: In comparison with Kr-81m, 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 fo r further additional testing to confirm or refute PE.