Most patients who are at risk of having a pulmonary embolism receive a CT angiogram to determine their susceptibility. However, the test exposes patients to high doses of radiation, which may increase the risk of breast cancer in young women.As reported in the September issue of The Journal of Nuclear Medicine, Dr. Alexander Gottschalk from Michigan State University in East Lansing and his colleagues from St. Joseph Mercy Oakland Hospital in Pontiac, Mich., from Wayne State University in Detroit and from Weill Cornell Medical College and Methodist Hospital in Houston analyzed data taken from PIOPED II — a large, multicenter clinical trial — for 824 patients with a suspected pulmonary embolism. The researchers examined whether a ventilation/perfusion lung scan, given in conjunction with an objective clinical assessment, is as reliable as a CT angiogram.A ventilation/perfusion lung scan involves a pair of nuclear scan tests that use radioactive material to measure ventilation (breathing) and perfusion (circulation). The scientists note that this type of scan exposes the breast to 70 times less radiation than a CT angiogram.The ventilation/perfusion lung scans were performed using single- or dual-head gamma cameras. CT angiography was obtained with four-, eight-, or 16-head scanners. Interpretation of the images from both types of scans was based on agreement between two readers.The researchers found that, in 56 percent of the patients (460 of the 824), an interpretation of very low probability of a pulmonary embolism was made from the ventilation/perfusion scan. From these patients, CT or digital subtraction angiography data was obtained in 440 cases, and an objective clinical assessment was made in 430. The ventilation/perfusion scans rated as low probability revealed that 8.2 percent of the patients (36 of 440) were likely to have the disease; 3.1 percent (eight of 259) were considered likely to have a pulmonary embolism when the objective clinical assessment and ventilation/perfusion scan were used together. Among women under the age of 40, 2 percent (one of 50) were likely to have the disease (when both the clinical assessment and ventilation/perfusion scan were used).When the ventilation/perfusion scans were combined with an objective clinical assessment of very low probability, the investigators found that the results were as reliable as those from the angiogram.The researchers believe their results indicate that a noninvasive ventilation/perfusion scan — when used with an objective clinical assessment — provides reliable information on whether a pulmonary embolism is present. They believe that the test is a good alternative to the higher-radiation procedure, especially for young women who are at risk for breast cancer.