MRIs and MRAs pose extremely little health hazards. Out of the millions of MRI scans conducted each year, the FDA gets around 300 reports. This is compared to the thousands of cases of leukemia, cancer of the brain, and other severe diseases that result from exposure to magnetic fields in other areas of the environment. The only significant hazard associated with an MRI scan is if you are a patient or staff member who can be exposed to excessive radiofrequency (RF) radiation. An MRI scanner uses strong magnets and a pulse of radiofieid to create detailed images of your body. The image results from variations in the strength of hydrogen atoms in different parts of your body. These variations in turn result from differences in the chemical composition of these parts. The pulse of RF radiation used by the scanner to detect these variations causes no harm to living tissue. However, it has been suggested that repeated exposures to high levels of RF radiation may cause cancer. There is some evidence that individuals who receive many MRI scans are at increased risk of developing tumors elsewhere in their bodies. However, there is also evidence that this risk decreases over time as people age. It is not known whether a similar risk applies to people who are already diagnosed with cancer.