How it Works
Dense tissues in the body, such as bones, absorb more X-rays and look white on the X-ray picture. Less dense tissues, such as muscles and organs, absorb fewer X-rays and look like varying shades of gray on the X-ray. Air is not dense at all, so it absorbs very few X-rays and appears black on the X-ray picture. Many internal structures are similar in density, which can make distinguishing the different shades difficult. Sometimes a contrast medium, or dye, may be used to make any structure through which it flows appear lighter or white on the X-ray picture. Most X-ray exams require two or more images to be taken. Some internal organs require multiple images from different angles.