There is no set time for how long a CT brain test is administered, depending on whether the patient has changes in the brain. A CT brain exam is only responsible for the changes that occurred before the exam at that time. Usually after a CT has been done and there have been no changes or abnormal changes in brain function, the CT can be responsible for a long time. If the brain reappears with changes in neurological function, it needs to be reexamined again. Radiation from brain CT examinations will remain in the body for some time, but it is less harmful and can be metabolized gradually by the body’s immune system, and appropriate CT examinations can be performed within a year. Brain CT is an X-ray that passes through the head and collects data through a computer to form an image that can distinguish whether there are any abnormal changes in the brain structure. For example, there are no congenital developmental malformations in the brain, acquired injuries, including brain contusions, subdural hematomas, and intradural hematomas caused by head trauma, long tumors, brain parasitic diseases, brain inflammation, demyelinating diseases, and vascular diseases of the brain, such as cerebral thrombosis, cerebral embolism, and cerebral hemorrhage. Any disease in the brain that causes structural changes in the patient can be seen by CT.