A method of controlling an X-ray in a computed tomography (CT) apparatus includes: acquiring scout images of an object setting an imaging region of the object in the acquired scout images determining an outline of transverse axes lengths of the imaging region based on the transverse axes lengths of the imaging region controlling X-rays emitted toward the object by adjusting a distance between elements of a transverse collimator of the CT apparatus according to the determined outline and reconstructing a cross-sectional X-ray image of the object based on X-ray projection data generated by detecting the controlled X-rays.
