Methods, apparatus and systems for controlling x-ray exposure during a scan with a computed tomography system are provided. The system includes an x-ray source, a collimator, and a detector array. The collimator includes a first cam configured to shutter an x-ray fan beam, generated by the x-ray source, in a first direction, a second cam located on an opposite side of a focal point of the x-ray source from the first cam, the second cam configured to shutter the x-ray fan beam in a second direction, the second direction being opposite from the first direction, and a cam drive configured to position at least one of the first cam and the second cam during the scan.