A new study of a commonly used imaging test of the chest to detect potentially deadly blood clots in the lung shows that extending the scan to the legs \"where the clots typically originate\" or adding a standard clinical assessment significantly improves physicians\' abilities to accurately diagnose pulmonary embolism. A sudden and potentially deadly blockage in a lung artery, pulmonary embolism affects an estimated 600,000 Americans each year, making it the fourth most commonly occurring cardiovascular problem in the United States . \"This study suggests that chest CT angiogram for detecting dangerous blood clots in the lung is good, but sometimes it is not enough,\" noted Paul D. Stein, MD, professor of medicine at Wayne State University , and lead author of the study. \"We can more accurately detect or rule out pulmonary embolism by taking pictures of the leg veins in addition to pictures of the lung arteries,\" he said.