Methods and systems for determining a motion amplitude of an object being scanned. For example, a computer-implemented method for determining a motion amplitude of an object being scanned includes determining an internal parameter set based at least in part on calibrating the scanning apparatus according to a first predetermined algorithm; determining an external parameter set based at least in part on a testing surface and the internal parameter set; determining a mapping relationship between a pixel coordinate system and a world coordinate system based at least in part on the determined internal parameter set and the determined external parameter set; determining a motion amplitude of the object in the pixel coordinate system; and determining a motion amplitude of the object in the world coordinate system based at least in part on the determined mapping relationship and the motion amplitude of the object in the pixel coordinate system.