A method of reducing the distance of rectilinear motion in a helical scan includes defining a rectilinear motion start point La and a rectilinear motion end point Lb within a region of interest ROI for which a CT image is to be created, collecting projection data from the rectilinear motion start point La to the rectilinear motion end point Lb, and creating a CT image at a desired image position in the region of interest ROI using the collected projection data.