The two images shown above were obtained using a knee phantom that was exposed on the table top (i.e., no scatter removal grid) and using the identical radiographic techniques (i.e., 65 kV and 3 mAs). Note that the x-ray tube voltage used is higher than that required for a foot (50 kV), but less than the voltage used for larger body parts (e.g., 80 kV for the pelvis). The only difference between these two images is that the one on the right had blocks of Plexiglas added adjacent to the knee phantom; this additional material produces a large amount of Compton scatter, which markedly degrades the image contrast seen in the knee region.