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Radiation doses can be cut in half in some CT procedures The radiation dose used in some chest computerized tomography (CT) examinations can be reduced by 50 percent without jeopardizing the radiologist's ability to make a diagnosis, a new study shows.    The study, of patients who had CT examinations without contrast media, was published in the August issue of the American Journal of Roentgenology (AJR), the journal of the American Roentgen Ray Society.   Dr. James G. Ravenel “We wanted to find the minimum radiation dose that is needed to still maintain a good quality CT image,” says James G. Ravenel, M.D., assistant professor of radiology. Ravenel and colleagues conducted the study at SUNY Upstate Medical University in Syracuse, NY.   “The higher the milliampere seconds (mAs) the higher the radiation dose (measured in mrem),” said  Ravenel. “We took six sets of images of 10 patients using between 40 mAs (90 mrem) and 280 mAs (600 mrem),” he said. Five radiologists reviewed all of the images for each patient, ranking them based on quality.  The reviewers were not aware of the dose used in each image.  “Prior to the study, the standard radiographic technique was 280 mAs,” said  Ravenel.  The radiologists could not tell the difference between images taken at 160 mAs (340 mrem) compared to those taken at 280 mAs, he said.   The reviewers could tell the difference in image quality when the dose was reduced to 120 mAs, (260 mrem) said Ravenel.  However, the reviewers agreed that the difference in quality would not affect the radiologist's ability to make a diagnosis. “The improvement in image quality when we increased the technique to 120 mAs wasn't worth the added radiation risk,” said  Ravenel.   “There were 27 million CT procedures done in 1997,” he said. CT examinations are about 10 percent of all radiologic procedures performed each year. This number could increase as CT is being used more to screen for lung cancer. “While the dose for an individual CT is low enough that the effect on a given individual cannot be easily measured, it is not trivial,” said Ravenel.   “It is our responsibility to balance dose with image quality to ensure that patient doses are kept as low as reasonably achievable,” he said. This study really only applies to chest CT without contrast. However, it is likely that dose reductions are possible in other studies, such as head CT and abdominal CT examinations, said Ravenel. “Radiologists need to take a look at their CT protocols and determine how low the doses can go without compromising diagnostic performance,” he said.