How ultrasound scans work

How does an ultrasound scan work?
26 January 2021


ultrasound image of baby in womb


Phil Sansom explains how ultrasound scanning works...

An ultrasound is a type of scan that you probably know as being useful for checking on unborn babies. It’s called ‘ultra’ because it uses sound waves at ultra high frequency - way higher than a human can hear - to get an image of a specific area of your body. The sound waves echo off the boundaries between different tissues, and a probe picks up the echoes and turns them into an image in close to real time. A bit like a bat using echolocation to observe its surroundings!

Ultrasound is not just for pregnancies. It’s great at monitoring most organs through your skin. And on top of these “external” ultrasounds, there are also internal ones, such as transvaginal scans that check on your ovaries or womb; or you could have what’s called an endoscopic ultrasound, where the probe is attached to a long tube and goes down your gullet, to spy on your digestive system.

Ultrasound scans work very well if the thing you’re looking at is close to the probe, like an organ that’s directly beneath the skin. They’re not very good at bones, joints, and things that contain air, like lungs.

The good news is that there are no known risks from the ultrasound sound waves. You don’t get exposed to radiation, and you don’t need a scanner the size of a room! But considerations come if you get an endoscopic ultrasound, which can be a bit more uncomfortable and cause temporary side effects like a sore throat. Luckily for these ones you’ll usually be sedated and have your throat numbed by anaesthetic.


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