Sonography, also called ultrasound imaging or ultrasound scanning, uses high frequency sound waves to obtain a real time visual image of the inside of the body. The image shows movement of blood and organs and the structure of internal tissues. Traditionally a sonogram will show a flat presentation of the examined region, but three dimensional images are also possible, as are 4-D pictures, which show 3-D images in motion. The picture is called an ultrasound or a sonogram.

Sonography is conducted the way bats, dolphins, and fishermen use sonar. When sound waves enter the atmosphere, they bounce off objects, creating an echo. When these echoed waves are measured, they can reveal the shape and movement of the object they struck. In an ultrasound, a transducer emits the sound waves and also records and measures the returning waves. The transducer is pressed to the skin, producing sound waves, and measuring the difference in waves that return. This instantly produces an image of the internal organs being examined.

Doctors use sonography to examine the inside of the body without using ionizing radiation. If a patient has pain, swelling, or infection, a doctor will commonly conduct an ultrasound to make a diagnosis. A sonogram is useful for looking at the heart, blood vessels, unborn fetuses in pregnant patients, ovaries, uteruses, thyroid glands, spleen, kidneys, bladder, pancreas, and gall bladder, amongst other organs. After a heart attack, a doctor may also use sonography to assess the damage to the heart.

Ultrasounds are also used to guide procedures such as needle biopsies, where an abnormal cell is removed from the body for laboratory testing. This is especially with breast biopsies. If there is suspicion of clotting or other blood flow obstructions, blood vessel narrowing, tumors, or congenital malformation, a doctor may use a Doppler ultrasound to examine and possibly diagnose the patient. A Doppler ultrasound follows the blood flow through arteries and veins in the neck, arms, legs, and abdomen. The three types of Doppler sonography are color Doppler, which uses color to show speed and direction of flow in blood vessels, the power Doppler, which works similarly to the color Doppler, but with more detail, and the spectral Doppler, which reformats blood flow measurements into graphs.

A patient getting an ultrasound should not expect pain or discomfort, unless the transducer is being placed on a sore area. Depending on the exact nature and reasons for the procedure, a doctor may ask the patient not to eat or drink for a period of time, to drink lots of water, or to not change daily activities at all. The doctor will likely position the patient face up and apply a clear gel that produces a warming effect on the site where the transducer will be placed. The gel is applied to minimize the chance of air pockets between the skin and the transducer so that the sound waves can be as accurately measured as possible. After the procedure, the skin will be wiped clean of the gel, no discomfort should be experienced, and the patient can resume normal activities.