X-rays and ultrasounds are both examples of medical imaging procedures. (Other diagnostic imaging modalities exist too, like CT or CAT scans, MRIs, PET scans, among others.)
X-rays are types of electromagnetic radiation probably most well-known for their ability to see through a person’s skin and reveal images of the bones beneath it.
They are roughly classified into soft X-rays and hard X-rays. Soft X-rays have relatively short wavelengths of about 10 nano meters (a nano meter is one-billionth of a meter), and so they fall in the range of the electromagnetic (EM) spectrum between ultraviolet (UV) light and gamma-rays. Hard X-rays have wavelengths of about 100 picometers (a picometer is one-trillionth of a meter). These electromagnetic waves occupy the same region of the EM spectrum as gamma-rays. The only difference between them is their source: X-rays are produced by accelerating electrons, whereas gamma-rays are produced by atomic nuclei in one of four nuclear reactions.
X-rays were discovered in 1895 by Wilhelm Conrad Röentgen, a professor at Würzburg University in Germany. According to the Nondestructive Resource Center’s “History of Radiography,” Röentgen noticed crystals near a high-voltage cathode-ray tube exhibiting a fluorescent glow, even when he shielded them with dark paper. Some form of energy was being produced by the tube that was penetrating the paper and causing the crystals to glow. Röentgen called the unknown energy “X-radiation.” Experiments showed that this radiation could penetrate soft tissues but not bone, and would produce shadow images on photographic plates.
An ultrasound scan is a medical test that uses high-frequency sound waves to capture live images from the inside of your body. It’s also known as sonography.
The technology is similar to that used by sonar and radar, which help the military detect planes and ships. An ultrasound allows your doctor to see problems with organs, vessels, and tissues without needing to make an incision.
Unlike other imaging techniques, ultrasound uses no radiation. For this reason, it’s the preferred method for viewing a developing fetus during pregnancy.
Most people associate ultrasound scans with pregnancy. These scans can provide an expectant mother with the first view of her unborn child. However, the test has many other uses.
Your doctor may order an ultrasound if you’re having pain, swelling, or other symptoms that require an internal view of your organs. An ultrasound can provide a view of the:
- brain (in infants)
- blood vessels