An x-ray calibration device (300) includes a core (302) including a first material with a first x-ray attenuation coefficient. The core (302) defines a cavity (306) that is configured to receive a plug of a different x-ray attenuation coefficient in order to alter the x-ray attenuation coefficient of the x-ray calibration device (300). The x-ray calibration device (300) also includes an outer layer (304) at least partially surrounding the core (302). The outer layer (304) includes a second material with a second x-ray attenuation coefficient, where the second x-ray attenuation coefficient is lower than the first x-ray attenuation coefficient.
