By selecting the voltage and current of the X-ray tubes, the image brightness can be changed.  The voltage changes the frequency spectrum of the radiation at the same time, and must therefore be optimized for the material of the measurement object. Different materials and voltage levels result in different maximum radiographic lengths. These must be considered when setting the parameters.

Seen in the image above the interrelation between tube voltage, work piece size, and work piece material:  the maximum possible radiographic length depends on the material composition and geometry of the object. The data can be used only as an approximate guideline.