When someone reports to an emergency room after any type of an accident or incident that might have resulted in a head injury, it's almost inevitable that the ER doctor is going to order one or more CT scans of the brain. We now see in virtually every case that comes through the emergency room that they are running CT scans, not only of the brain but of other areas of the body.
What is a CT scan? It's a series of very specific x-rays that take a slice of the brain. They do them in this series format to show a very detailed image of the brain. They are excellent at diagnosing acute brain injuries where there is bleeding or acute damage to the brain that the CT scan is designed to pick up.
But many times a person may have an actual brain injury that doesn't manifest or show in the form of something a CT scan can pick up in the emergency room. When you move past that emergency period, maybe two or three days later, now the MRI typically becomes more of a tool to diagnose or find a brain injury.
Remember that a negative CT scan at the emergency room or even a negative MRI taken some days later, does not mean there is no injury to the brain. You can still have significant damage that these scans may not pick up.