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Pulmonary thromboembolism: a retrospective study on the examination of 991 patients by ventilation/perfusion SPECT using Technegas.

PURPOSE
Conventional planar ventilation/perfusion (V/P)-imaging in those patients suspected of suffering from pulmonary thromboembolism (PTE) is of limited diagnostic value. It is the purpose of this retrospective study to determine whether the use of V/P-SPECT using Technegas might reduce the rate of those diagnostic uncertainties and might lead to better results.


METHODS
991 patients (660 female, 331 male, age 18-90, mean 60), referred to our laboratory with suspected PTE, were examined as follows: patients inhaled 37 MBq of Technegas in the supine position and a SPECT-acquisition was started. Following SPECT-completion, 185 MBq 99mTc-MAA was injected intravenously. SPECT was then repeated. Coronal and transverse ventilation and perfusion SPECT-slices were reconstructed and compared section by section. 85 patients underwent control scans by the same technique at a mean interval of 22 months after the original scans.


RESULTS
As the SPECT images in almost all cases made a clear match/mismatch decision possible, we categorized all patients as embolic (PTE+) if there was at least one mismatching defect, and as non embolic (PTE-) if there were none. Our results were: PTE+: 178 patients (18%), PTE-: 808 patients (81%), uncertain: 5 patients (0.5%), if 34 triple-match defects are included: 39 patients (3.9%). 46 patients, categorized as PTE+ underwent a control V/P scan after anticoagulant therapy. In 44 of these patients, PTE was confirmed by the controls. In a control group of 39 PTE- patients, control scans were unchanged in 38 cases. From these observations we can calculate a sensitivity of 96% and a specificity of 97%.


CONCLUSION
We conclude that V/P imaging can be improved significantly by V/P SPECT using Technegas.