Ultrasound scans (sonography) make it possible to see inside the body by using sound waves above the range of human hearing and converting their “echoes” into images. A special device is used to send the sound waves to the part of the body that is to be examined. Depending on the kind of tissue, the waves are either reflected a lot (e.g. fluid-filled body cavities), a little, or are not reflected at all (e.g. bone tissue). The echoes are converted into a spatial image of that part of the body, which is made visible on a fluorescent screen. Ultrasound scans are typically used for diagnostic purposes in pregnancy, for the diagnosis of problems in the abdominal cavity, such as gallbladder and kidney problems, as well as to examine the thyroid gland and blood vessels.