Brain CT radiation exposure is usually higher than the received dose during a radiography of the head. Radiation dose from CT procedures varies based upon the type of procedure (slice thickness, number of slices, etc.), the type of CT equipment and its operation, so without knowing these details it’s hard to say how much radiation is received.
An estimate can be performed by a radiation physicist based on the number of CT slices and technique used to determine total exposure to a person. However, the CT scan is more detailed and has better soft tissue discrimination than an x-ray that the benefit usually outweighs the risk.
MRI scans provide high soft tissue contrast without radiation. The appropriate diagnostic imaging modality is depending on the indication and requested information.