Physics: Ultrasound

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  • Created by: eloise
  • Created on: 16-04-13 21:32

What is ultrasound?

Ultrasound is waves at a higher frequency than we can hear.

Electrical systems can be made which produce electrical oscillations of any frequency.

These can easily be converted into mechanical vibrations to produce sound waves of a higher frequency than the upper limit of human hearing. The range of human hearing is 20Hz to 20, 000Hz. This is called ultrasound.

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Ultrasound waves get partially reflected at a boun

When a wave passes from one medium into another, some of the wave is reflected off the boundary and some is transmitted (and refracted) this is called partial reflection.

What this means is that you can point a pulse of ultrasound at an object, and wherever there are boundaries between one substance and another, some of the ultrasound gets reflected back.

The time it takes for the reflections to reach a detector can be used to measure how far away the boundary is.

This is how ultrasound works.

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Oscilloscope traces are used to find boundaries

An oscilloscope can visualise when these partial reflected waves are detected.
The oscilloscope will have an image of waves when they are detected and a straight line when none are detected.
The screen shows time divisions along the bottom.

If you know the speed of sound In the medium, you can work out the distance between boundaries using this formula:

s = v x t

S is distance in metres, m
V is speed in metres per second, m/s
T is time in seconds, s

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Ultrasound in medicine

Investigating blood flow in organs, diagnosing heart disease and check
No on feral development Andre all uses of ultrasound in medicine.

Breaking down kidney stones.

Kidney stones are hard masses which can block the urinary tract.
An ultrasound beam concentrates high-energy waves at the kidney stone and turns it into sand-like particles.
These particles then pass out of the body in the urine.
It's good because the patient doesn't need surgery and it's relatively painless.

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Ultrasound in medicine

Pre-natal scanning of a fetus.

Ultrasound waves can pass through the body, but whenever they meet a boundary between two different media (like the fluid in the womb and the skin of the fetus) someof the wave is reflected back and detected.
The exact timing and distribution of these echoes are processed by a computer to produce a video image of the fetus.

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Compromises in medical imaging

Doctors have to make compromises between getting a clear enough image to diagnose problems, whilst putting the patient at a low risk as possible.
X-ray and ultrasound imaging both have their advantages and disadvantages..

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Is it safe?

Ultrasound waves are non-ionising and,as far as anyone can tell, safe.

X-rays are ionising. They can cause cancer if you're exposed to too high a dose, and are definitely NOT safe to use on developing babies.

CT scans use a lot more X-ray radiation than standard x-ray photographs, so the patient is exposed to even more ionising radiation. Generally CT scans aren't taken unless they are really needed because of the increased radiation dose.

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What about image quality?

Ultrasound images and typically fuzzy - which can make it harder to diagnose some conditions using these images,

X-ray photographs produce clear images of bones and metal, but not a lot else.

CT scans produce detailed images and can be used to diagnose complicated illnesses, as the high resolution images can make it easier to work out the problem. High quality 3D images can also be used in the planning of complicated surgery.

happy revision, GOOD LUCK :)

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Could you go over calculations, like calculating resolution with pulse duration and wave speed?

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