MRI, CT scan use spikes, study finds. Should we be worried? By Robert Bazell, Chief science and medical correspondent, NBC News The latest medical images can provide spectacular pictures, giving doctors and patients enormous amounts of information about a wide range of medical conditions. But doctors may have gotten overly enthusiastic about using them. A study out Tuesday in the Journal of the American Medical Association found that the number of MRIs quadrupled, CT scans tripled and PET scans went up 57 percent between 1996 and 2010. The researchers tracked up to 2 million members of six large health systems in the U.S. There is no question that before performing a surgery, for example, a doctor wants to see as much as possible. Magnetic Resonance Imaging (MRI) uses magnets and radio frequency fields to scan the body and help doctors make diagnoses of tumors, torn ligaments or strokes without surgery. A PET, or positron emission tomography, scan can be conducted alone or combined with MRI with radioactive isotopes to show metabolic activity in the body such as cancer. The images help; the question is just how much. "The increase in use of advanced diagnostic images has almost certainly contributed to both improved patient care procedures and outcomes, but there are remarkably few data to quantify the benefits of imaging," radiology professor and lead author Dr. Rebecca Smith-Bindman from the University of California, San Francisco, and her colleagues write. Why does it matter? The biggest reason is cost. Americans now spend an estimated $100 billion a year on medical imaging. For each patient, each procedure can cost between a few hundred and several thousand dollars. Usually doctors order them for the best of reasons, but sometimes it is defensive medicine based on the fear of lawsuits or, even worse, the need to amortize the huge cost of a piece of equipment the practice has purchased. Another major downside of increased imaging is the "false positive," which is the discovery of a growth or other apparent problem that presents no danger but needs to be removed -- with additional cost and anxiety. The biggest danger with scanning comes from CT, or computed tomography. A CT scan exposes the patient to huge amounts of X-rays. One CT scan of the chest, for example, zaps a patient with the same amount of radiation as 150 old-fashioned X-rays. In their survey of medical records, the authors of the latest study found that 3.9 percent of patients were receiving an exposure or more than 50 millisieverts every year. In comparison, that is about the equivalent of the one-time amount that the Japanese government estimates that the nearby residents of the Fukushima power plant got in the hours before they evacuated. A recent Institute of Medicine report on risk factors for breast cancer listed chest CT scans high on the list. Last week, an international study found that children who get CT scans have a slightly higher risk of later developing leukemia and brain cancer. While the absolute risk of cancer is still small, the British researchers suggested minimizing radiation exposure as much as possible. In a separate report released by the UCSF researchers Monday, Smith-Bindman said a woman should ask her doctor these questions before getting a CT scan: Is this scan absolutely necessary? Is it necessary to do it now? Are there alternative tests? How can I be sure the test will be done in the safest way possible? Will having the scan information change the management of my disease? For the sake of our pocketbooks and peace of mind, we all might be well advised to ask our doctors the same questions about any medical scan we receive. Robert Bazell is NBC's chief science and medical correspondent. Follow him on Facebook and on Twitter @RobertBazellNBC More health news: