1. An imaging system comprising: an identification module configured to identify a scanning mode of operation; an analysis module configured to determine an attenuation for an object for a scan to be performed on the object; and a determination module configured to: determine an image contrast for each of plural setting combinations; determine a corresponding tolerable noise for the image contrast for each of the setting combinations based on the scanning mode of operation; determine a corresponding diagnostic dosage for each setting combination, the diagnostic dosages corresponding to the image contrast and tolerable noise for the corresponding setting combination; and select an operational setting for the scan to be performed using the dosages determined.