Difference Between X-ray and Ultrasound

Main Difference – X-ray vs Ultrasound

Nowadays, both X- Ray and ultrasound are used in many industrial, scientific, and medical applications. In medicine, both X- ray and ultrasound are used to identify some disorders in the body. Anyhow, X- ray and ultrasound are very different. The main difference between X-ray and ultrasound is that X-rays are electromagnetic transverse waves whereas ultrasounds are mechanical longitudinal sound waves. X- Rays can ionize atoms in a medium whereas ultrasounds cannot. There are dozens of such differences between X- ray and ultrasound. Some of those differences are discussed in this article.

What is X-Ray

X- Rays are high- frequency electromagnetic waves discovered by Wilhelm Rontgen. The energy of an X- ray photon with frequency f is given by E= hf. (where h is the Plank constant). Normally, electromagnetic waves with energies in the range of 100 eV-100keV are considered to be X- rays. X- Rays having photon energies less than 5keV are normally referred to as soft X- rays. Their penetration capability is less. High energy X- rays having photon energies above 5keV are called hard X- rays.

Hard X- rays are widely used in radiography as they can penetrate through tissues. In addition, high energy X- rays are used in medicine as a cancer therapy.

The wavelengths of X- rays are much shorter than that of visible light and comparable with atomic radii. So, higher resolutions can be achieved by using X- rays (X- Ray crystallography).

In general, X- ray tubes are used to produce X- rays. Anyhow, the X- ray tube concept is not an efficient method because a significant portion of the input energy is released in the form of waste heat. In some applications, X- ray tubes are replaced with small particle accelerators that use an efficient technique. 

X- Rays are highly energetic. So, they can ionize neutral atoms or molecules. The X- ray exposure increases the risk of cancer as a result of its ionizing capability. Simply, X- rays are very useful for treating cancers. But the same treatment can be a carcinogen, unfortunately.

Difference Between X-ray and Ultrasound

What is Ultrasound

The human hearing range is normally considered to be 20 Hz- 20 kHz. So, sounds within this range are called audible sound. Sounds which are above the human limit of hearing are called ultrasound. In other words, sound waves with frequencies above 20 kHz are referred to as ultrasound waves. So, ultrasound waves are mechanical acoustic waves. They need a medium for the propagation.

Even though human ear is incapable of sensing ultrasound, some animals such as bats and dolphins can produce and hear ultrasound. They use ultrasound for navigation in pitch darkness. These animals are natural sources/ detectors of ultrasound.

There are many applications of ultrasound in medicine, industries, communication, military, navigation, research, and many other fields. Especially, applications of ultrasound play a vital role in medicine (ultrasonography). Ultrasonography is a very effective, safe and harmless diagnostic technique. Most of the medical ultrasonic equipment use the Doppler shift and echo time of the reflected ultrasound waves to collect the required information from organs and other components of the body.

Normally, piezoelectric crystals are used to produce ultrasound. Piezoelectric crystals can be deformed by applying a potential difference. This effect is referred to as the inverse piezoelectric effect. The degree of the mechanical deformation depends on the potential difference applied. Higher the potential difference higher the deformation. So, these crystals can be oscillated with a desired frequency by applying an AC voltage, and the oscillating crystal produces ultrasounds.Main Difference - X-ray vs Ultrasound

Difference Between X-ray and Ultrasound

Type of the wave:

X- rays are electromagnetic waves.

Ultrasound waves are mechanical acoustic waves.

Nature of the waves:

 X – ray is a transverse wave. A material medium isn’t needed for the propagation.

Ultrasound is a longitudinal wave. A material medium is needed for the propagation.


 Xrays have the frequency of 3 Hz to 3 Hz.

Ultrasound frequencies are above the human higher limit of hearing (20000 Hz).


X-ray is used in X-ray fluorescence (non-destructive elemental analysis), Radiography in medicine, X- ray lithography, X- ray therapy, X- ray crystallography, etc. are some applications of X-ray.

Ultrasound waves are used in ultrasound imaging, sonar devices, non-destructive testing, acoustic microscope, ultrasound cleaning, etc. are some applications of ultrasound.

Ionizing capability:

X- rays can ionize atoms.

Ultrasound cannot ionize atoms.


 X- rays are highly energetic waves, so they can interact with DNA and cells. This ability of X- rays carry the risk of cancer.

Ultrasound waves are mechanical acoustic waves. Therefore, they do not carry any risks.Difference Between X-ray and Ultrasound -infographic

Image Courtesy:

“X-ray waves” by Ulflund – (CC BY-SA 3.0) via Commons Wikimedia

Ultra sounds” by Ultrasound_range_diagram.png: Original uploader: LightYear at en.wikipediaUltrasound_range_diagram_png_ (CC BY-SA 3.0) via Commons Wikimedia 

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