This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular Radiology, Subject name: Radiology
Which of the following describes the Westermark sign in Pulmonary Thromboembolism? 
Select and explain. 
A. Peripheral Wedge shaped infarct, B. Pulmonary Oligemia, C. Prominence of Main Pulmonary Aery, D. Prominence of Descending Rt Pulmonary aery
B: Pulmonary Oligemia
Answer: B: Pulmonary Oligemia 
Explanation: Sign in Pulmonary Thromboembolism: * Fleischner sign: enlarged pulmonary aery * Hampton hump:peripheral wedge of airspace opacity and implies lung infarction * Westermark sign:regional oligemia and highest positive predictive value. * Palla sign: enlarged right descending pulmonary aery * Chang sign: dilated right descending pulmonary aery with sudden cut-of