V/Q scan less radiation risk than CT

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Educating physicians about ventilation-perfusion (V/Q) scanning as an alternative to CT for the diagnosis of pulmonary embolisms led to a 23 percent decrease in patient exposure to radiation, according to a study presented today in Boston at the 2009 annual meeting of the American Roentgen Ray Society (ARRS).

"VQ scanning is a nuclear test which shows blood flow to the lung and airflow. When there is a pulmonary embolism, the air can enter normally, but the blood flow will be disrupted, resulting in an abnormal scan," said the study's lead author, Linda Haramati, MD, from Albert Einstein College of Medicine, Montefiore Medical Center in Bronx, N.Y.

"We are very conscious of radiation exposure in our population," said Haramati. She said that collaborative and educational seminars were held between radiology, nuclear medicine and emergency medicine departments regarding the radiation dose and comparable sensitivities of VQ and CT pulmonary angiography for pulmonary emboli.

In the study, Hamarati reported that the patients were similar in age for CT and V/Q in 2006 while the patients who underwent V/Q were significantly younger in 2007. The proportion of CT and V/Q interpreted as negative and positive, and indeterminate for V/Q did not change between 2006 and 2007. V/Q was more often negative than CT in both 2006 (89.4 vs. 84.8 percent) and 2007 (89.4 vs. 81.8 percent), each. There was no significant difference in the false negative rate (range 0.8-1.2 percent) between CT and V/Q in 2006 and 2007.

"The proportion of CT to VQ changed dramatically after our seminars. In 2006 about 60 percent of the studies were CT, while in 2007, about 60 percent were VQ. When we looked at radiation exposure, the mean effective dose was reduced by 23 percent, from 11.5 mSv in 2006 to 8.9 mSv in 2007," she explained.

"CT confers a much higher radiation exposure than VQ scans. However VQ scans are harder to interpret in patients with abnormal chest x-rays, so we, along with our emergency department physicians, have decided to perform VQ scans as the preferred imaging modality in patients with normal chest x-rays who were suspected of having pulmonary embolism--in order to decrease radiation exposure," Haramati said.

The authors concluded that "practice patterns of emergency department physicians changed rapidly in response to an interdepartmental educational intervention promoting simple chest radiography triage for patients with suspected pulmonary embolism. Utilization of V/Q increased while CTA decreased, resulting in a reduction of patient radiation exposure without compromising safety and efficacy."