A i.e. Lung ventilation - perfusion scan The clinical picture depicted is suggestive of a case of Pulmonary thromboembolism (PTE) An elderly man on bed rest for past 10 days : predisposed for deep vein thrombosis complaints of breathlessness & chest pain. A chest X-ray in patient of PTE may well be normal or near normal Diagnostic strategy in cases of suspected PTE Chest X Ray / Quantitative Plasma-D-dimer-Elisa (reflects plasmin break down of fibrin & indicates endogenous thrombolysis, has high negative predictive value & can be used to exclude PTEQ) Lung Ventilation Perfusion Scan (noninvasive, after CXR, a V-P Scan is the most commonly requestedQ imaging investigation for a suspected case of PTE) Nondiagnostic High probability Leg Ultrasonography Treat Normal Pulmonary AeriographyQ (most definitive diagnostic methodQ but invasive & costly so done when dx can't be confirmed by other methods) Most Specific test for establishing a diagnosis of pulmonary thromboembolism is pulmonary aeriogramQ. Most frequent used imaging investigation for suspected Pl'E is V-P ScanQ. It uses IV injection for Tc99 labelled albumin or inhalation of radioactive gas (Krypton-81, Xenon-133, Tc99 DTPA or Carbon paicles Known as Techegas) The cardinal sign is Mismatched Perfusion defectQ (i.e. under perfused pa of the lung on perfusion scan while the ventilation scan remains normal). On CXR, Hampton's HumpQ d/t pulmonary infarct is seen.