<prompt> In patient with high clinical suspicion of pulmonary thromboembolism, best investigation would be?D-dimerCT angiographyCatheter angiographyColor Doppler  <response>: 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 bo 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 cant 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. 