A CT scan, or CAT scan, is a very helpful and commonly ordered test that you will encounter no matter where you are in the world. It is indispensable in providing a non-invasive look at your internal organs and the speed of the examination makes it the best choice for doctors to order so they can make a quick decision to potentially save a patient's life. Even with all these advantages, like everything else in life, there are distinct disadvantages that you need to be aware of as well before you lie down on the examining table for your next CAT scan.
One disadvantage of living in the developed world is the abundant access to medical imaging studies. No need to reread the sentence, you read that right. Almost every hospital in North America, especially in the United States will have access to a CT and MRI machine. The standard practice of care is to send the patients coming into the ER straight to the CT room in order to have a test ordered. The print-out that comes back will be what will then determine what the next step in management for the patient will be.
This is a rather antiquated approach to medicine that hospital directors are trying to stifle in the United States due to the high costs of imaging studies and the adverse impact it can have on the quality of life in a patient. Even if the acceptable standard of care would be to only do a CT scan when absolutely necessary, there is still a lag in the acceptable standard of care and the current standard of care in use so patients can easily have unnecessary imaging studies done.
The most obvious risk of common exposure to CT scans would be from radiation exposure. CTs are effective because they are able to generate images of your body using X-rays. When you have one CT scan done, you will be exposed to a small amount of radiation but the dose is so small that you will not have any additional risk to your life. A normal CT posses little to no threat to your health but you should try not to have more than one CT done per year to help reduce your chances of developing cancer. Most hospitals are now digitalized so if you have had a study done at a different hospital, advise your doctor to track down the CT scan first before needing to do an unnecessary study.
CT scans can also be part of a more complex diagnostic test for patients. Coronary angiographies are necessary to make sure patients do not have an increased risk of heart attacks. Studies have recently shown that an estimated 1 in 270 women at the age of 40 and 1 in 600 men will develop cancer directly from radiation exposure after CT scanning. A head scan could produce risks like 1 in 8,100 women and 1 in 11,080 men.
As you can see, the risk is higher but in these circumstances, the risks of not doing the study are far more damaging to your health than choosing not to do the study due to fear of radiation. 
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