In patient with high clinical suspicion of pulmonary thromboembolism, best investigation would be?

B i.e. CT angiography Spiral or helical chest CT scan with intravenous contrast (CT pulmonary angiography) is the principal imaging test for the diagnosis of pulmonary embolsmQ. It acquires image with < 1 m resolution and visualizes up to 6th order branches and small peripheral emboli with a resolution superior to conventional invasive contrast pulmonary angiography. It obtains excellent images of right & left ventricle and can be used for diagnosis as well as risk stratification. In patients with pulmonary embolism, RV enlargement indicates 5 times more likelihood of death within next 30 days. Inadequate breath holding can impair the image quality b/o change in aerial flow rates and motion aefact during breathing. The advent of multidetector CT (MDCT) allows examination of whole lung during single breath -hold. It is noninvasive. Ventilation - perfusion lung scanning is now second line diagnostic testa for PE, and mostly used in patients who cannot tolerate intravenous contrast. Its utility is greatest when accompanied with a normal chest x-ray implying that a ventilation - perfusion mismatch is not due to parenchymal disease. High probability (>80%) scan have 2 large segmental V-P mismatches (perfusion defects & normal ventilation) with a normal chest radiograph. And very low probability scans have micropaicles (10 - 100 1.1 m) of Tc99 micro - aggregate albumin (MAA) in patients lying supine. Ventilation scintigraphy is performed by inhalating Krypton - 81, (best), Xenon 133, Tc99 - diethylenetriamine penta acetic acid (DTPA), or technegas. Last two can't be administered during perfusion scan as both are labelled with Tc99. Eight images (anterior, posterior, obtique & lateral on both sides) are aquired. Conventional pulmonary angiography: Non invasive CT with contrast have viually replaced invasive pulmonary angiography as a diagnostic tool. However, it remains the gold standard testa.