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Diagnosing or ruling out pulmonary embolism without subjecting patients to pulmonary angiography is one of the most difficult problems in medicine. This multicenter study, from the NIH's Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED), demonstrates that ventilation/perfusion lung scans offer only limited help.
Investigators reviewed lung scans in 755 patients who also underwent pulmonary angiography, 251 (33 percent) of whom were confirmed as having emboli. Nearly all patients had abnormal scans (designated as low, intermediate, or high probability) whether they had pulmonary emboli or not. Of the 251 patients with emboli, only five had normal or near- normal scans, but 39 had "low-probability" scans. At the same time, onl…