Computed tomography –or CT–scans have become a powerful imaging tool for diagnosing disease. Health-care providers performed more than 70 million CT scans in the United States in 2007.
A December 2009 study in the Archives of Internal Medicine calculated that those 70 million scans could lead to 29,000 cancers. That figure is a statistical calculation and “there is no direct evidence linking the radiation dose from CT scans to cancer,” says Cynthia McCollough, a radiological physicist at the Mayo Clinic. “Doses delivered in a CT scan are of the same magnitude that we get every year from background radiation.” (A typical CT scan might result in a dose of one to 14 millisieverts. )
Nevertheless, the CT community is looking for ways to reduce the radiation dose from scanners. This is because CT scans are becoming more common, and because multiple scans are often required for some patients such as those suffering from head or spine trauma . Some promising techniques for reducing CT scan radiation were recently presented at the meeting of the American Association of Physicists in Medicine in Philadelphia.
Researchers at GE Healthcare in Waukesha, WI, presented a technique that needs roughly an eighth of the radiation dose of today’s scanners to create an image just as sharp and with the same high resolution. “Dose reduction depends on a case-by-case basis and the application,” lead scientist Girijesh Yadava says. “You could go lower or higher [than an eighth] depending on the part of body.”
A CT scanner puts together multiple cross-sectional images to create a detailed picture of body structures. An x-ray tube rotates around the patient and directs beams into the body from different angles. After the rays pass through the body, their intensity is measured by an array of detectors on the other side. A computer algorithm then reconstructs images from the intensity data. Just as each light detector in a digital camera corresponds to an image pixel, each detector gives a voxel, or volume element, of the image.