Final answer:
High optical density streaks on radiographs can be caused by greater attenuation due to the Compton effect or the presence of substances with a high atomic number like barium or iodine that increase contrast.
Step-by-step explanation:
A streak of high optical density on the finished radiograph can be caused by greater attenuation of x-rays in a particular area of the image. This is often related to the phenomenon known as the Compton effect, where as x-ray energy increases, x-rays scatter from an outer electron shell of the atom, affecting image quality. Low-energy x-rays usually provide better contrast for sharper images. In certain areas, increased optical density can occur if a part of the body has been injected with a substance that has a large atomic number, such as barium or iodine, which can significantly increase contrast against the surrounding tissue in the radiograph.