A method for controlling operation of a pre-patient collimator to sweep x-rays across a patient are described. Particularly, and rather than shuttling the patient back and forth to obtain scans of different locations, the x-ray beams are swept across the patient by adjusting the positions of the pre-patient collimator. The x-ray beam deviates from the nominal position in z (z is the axis perpendicular to the scan plane). Since the pre-patient collimator is very light, and since the amount of motion in collimator is very small due to the large magnification, the x-ray beam deflection can occur instantaneously without any ramp-up or ramp down periods. Therefore, a 100% duty cycle can be achieved and the image update rate may be reduced. Also, no modification to the reconstruction process is necessary. The nominal slice location for each reconstructed image can be easily estimated by the centroid of the beam location during the date acquisition.
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