1. A computed tomography (CT) scanner, comprising: an x-ray source; an x-ray detector; and a computer system operatively coupled to the x-ray source and x-ray detector, and configured to perform the steps of: obtaining a patient size data; establishing a target noise equation, the target noise equation being a function of the patient size data; and applying the target noise equation against a measured noise equation, the measured noise equation being a function of the patient size data, to derive CT scan parameters for a given CT scan.