A brain injury can be diagnosed by a number of different tests. The ease by which the diagnosis is made can depend upon the severity of the injury. For example, in cases of a severe brain injury, diagnostic studies such as an ultrasound, CT scan, or MRI will almost always reveal the diagnosis. In cases of a more mild brain injury, some of these same diagnostic tests are not expected to make the diagnosis. Neuropsychological testing with standardized tests is often necessary to identify and measure the extent and severity of a brain injury. Additional, special brain imaging tests such as PET scan or QEEG can help make the diagnosis.