A cranial CT scan involves in a younger child an anaesthetic, and usually is performed in older children when lying still, and we look with special x-rays on the computer to determine whether there are any abnormalities within the head. It is particularly helpful for looking for abnormalities involving any abnormal structures, such as the collecting system of cerebral spinal fluid and also for any tumours and any raised pressure inside the head, but generally we have moved over to MRI scan which doesn't involve radiation for indications noted here.