Ultrasound – Why it is necessary to drink water before it?

USG thumbnail

We are very much aware of the word USG or Ultrasound. When a lady gets pregnant, she undergoes many tests for better prevention and cares for her baby. Ultrasound is the sound wave of very high frequency 2.25 MHz to 7.5 MHz (Usually 3.5 MHz is used). The sound wave is known as ultrasound and the process of imaging baby inside the pregnant lady through it is known as USG (Ultrasonography).

What is USG?

Medical ultrasound is a diagnostic imaging technique or therapeutic application of ultrasound. It is used to create an image of internal body structures such as tendons, muscles, joints, blood vessels, and internal organs. Its aim is often to find a source of a disease or to exclude pathology.

Doctors suggest us to drink as much as water before it. Also, doctors prohibit eating food before the test. But ever think of it why it is necessary to drink water before Ultrasound? The ultrasound wave is not capable of traveling in an air medium as it depends upon the density of the medium.

Why it is necessary to avoid food before Ultrasound (USG) test?

Eating food at any time allows acid to flow in the stomach which helps in the digestion of food. This acid is also responsible for forming gas in the stomach which is considered as a disturbing factor for the transmission of the ultrasound wave. Thus, doctors suggest not eating food before the test.

The acoustic impedance of a material or tissue describes its stiffness and flexibility to the ultrasound beam. The units of acoustic impedance (kg/m2s) are expressed as the SI units of rayls (1 kg/m2s = 1 rayl)
Z= Density (kg/m3) x Speed of of sound (m/s)

MediumZ (Rayls)
Air0.0001
Fat1.4
Water1.5
Average tissue1.6
Muscle1.7
Bone8.0

-You may like to read-


Why it is necessary to drink more and more water before Ultrasound (USG) test?

Woman drinking water before ultrasound

An ultrasound when passing through the human body travels through bone, muscles, average tissue, fat, and air in the stomach. If we drink more and more water then indirectly we are replacing the air by water which is responsible for good imaging quality of USG. So when the image is not clear it is considered that air is still present in the area of imaging and causing a disturbance in the imaging technique. At that time patient becomes angry but there is nothing to do by the doctors rather they are helping us to get a better result.

Why can’t we here it if it is a sound?

Generally, the speed of the sound is 340 meters per second and the audible frequency is within the range of 18.000-20.000 hertz (18-20 kHz). But the frequency of the ultrasound used in USG is very high 3.5MHz. So, it is out of range to hear for human beings. But the interesting fact is that few animals like dogs, bats, and dolphins van hear these high pitch sound waves.

So I hope you have understood the need for water at the time of USG. So, please cooperate with the doctors and help yourselves to get better results.

Thank you!!!!

Also read: Why Does Sound Travel Faster In Hot Summer Days Than In Cold Winter Days?

Share Knowledge
Jaikamal is a very fluctuating mind person who always looks for knowledge or resources of knowledge. He believes that knowledge is the key to success.

One thought on “Ultrasound – Why it is necessary to drink water before it?

Leave a Reply

Back To Top