MA is a 68-year-old female with lung cancer. She had been a bedridden patient in the hospital for the past 3 days due to the development of pericardial effusion related to the cancer. One morning she complained of a marked increase in breathlessness and chest pain. Upon examination, her physician observed that his patient had dyspnea, tachypnea, tachycardia, rales, and a fever. He ordered a nuclear scintigraphic ventilation-perfusion scan of her lungs. It was determined that MA had a moderate-sized