Physics of Medical Scans
Image Source: Frisbie Memorial Hospital
What is it?
An ultrasound scan is a way of looking inside your body using sound waves, and it means you can check that your body is working the way it should be.
You probably picture it being used to look at a baby inside a mother’s tummy, but it can be used for many more things, like looking at your heart and other organs, or your blood.
What is it like?
Most ultra sound scans don’t last very long (between 15 and 45 minutes), and they usually happen in a hospital.
The most common scan with ultrasound is done from the outside of your body [1].
A doctor or nurse will use a small handheld machine (called a “probe”) to send the sounds into your body so that they can see inside.
They will put a gel on your skin (for example on your tummy or chest) which will feel quite cold, but other than that you won’t feel a thing!
This gel helps the sounds go into your body, and also helps the machine move smoothly across your skin.
Depending on what needs to be looked at, you might have to not eat before the scan, or you might have to have the scan just before you need to go to the toilet for a wee. This is nothing to worry about and straight after the scan you will be able to eat or go to the toilet.
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Sometimes scans need to be taken from inside your body so you can see further in. This would mean a small tube (that can make the ultrasound waves) would be put inside your body (for example in your throat).
This might be a little uncomfortable, but you would be given some medicine to make you feel better, and it wouldn’t last for too long.
You might have to stay in the hospital for a little bit after this because the medicine will make very sleepy.
How does it work?
The machine sends ultrasound waves into your body, they then bounce off the different parts inside, and then come back to the machine. This is just like when you shout in a wide open space and you can hear your voice echo back to you: the sound is just bouncing off objects and coming back, like how the ultrasound waves bounce off the organs and different things inside you and go back to the machine.
When the sound come back to the machine it is turned into a moving picture on a screen so that the nurse or doctor can look at your organs and check that they are working properly.
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References:
[1] NHS Ultrasound Scan: https://www.nhs.uk/conditions/ultrasound-scan/ (accessed 13/02/19)
An ultrasound being carried out
(source: News Medical)
Ultrasound scan of the baby in a mother's tummy
(source: Ultrasoundkk)
What is an ultrasound wave?
Ultrasound waves are just like the sound waves you make when you speak, except they are much too high pitched for humans to hear!
Want to know a fun fact about ultrasound waves?
Bats can hear ultrasound waves and use them to see where they are going. They make sounds and listen for the echoes to see where the objects are, just like in the ultrasound machine!
Just like the person hears their voice echo back from the wall, the ultrasound probe "hears" the ultrasound waves echo back from the baby in the stomach!