P3 Medical Applications Of Physiscs Flashcards
How do X-rays work?
Rays are transmitted by (pass through) tissue but pass are absorbed by bone and metal as they are denser.
They affect photographic film in the same way as light meaning they are put under a limb and show the bones inside.
They can diagnose bone fractures and dental problems.
Electronically formed images are made by charge coupled devices. They are silicon chips he size of a stamp dividend into millions of pixels. CCDs detect X-rays and produce electronic signals that form high resolution images.
What are X-rays?
High frequency, shortwave length electromagnetic waves.
Explain how a CT scan works.
Computerised axial tomography use X-rays to produce high resolution 3D images of hard and soft tissue. The patient is put inside a tube and has X-rays fired through him by an X-ray tube. These are detected by detectors on the other side. The X-ray tube is rotated during the scan producing many 2D images which a a computer stitches together to form a 3D image.
They can see soft tissue as it absorbs small amounts of radiation and lots more X-rays are used in CT scans. This means tiny variations is tissue density can be found.
Why can X-rays be used to treat cancer?
They cause ionisation meaning high does kill living cells. They can treat cancers but have to be focused at the right place and at the tight dosage to stop too many health cells being killed.
How are X-rays used to treat cancer?
X-rays are focused on a tumour using a wine beam.
This is then rotated with the tumour remaining at the centre.
This minimises the exposure normal cells feel se reduced the the affect on healthy cells.
How do radiographers stop themselves dying when doing their job?
They wear lead aprons, stand behind a lead screen or leave a room while the scan takes place.
Lead is also used to shield areas of the patients body and the exposure time is kept to a minimum.
What is ultra sound and how is it generated?
Electrical systems can produce electrical oscillations of any frequency.
These are converted into mechanical vibrations that produce sound that humans can’t hear. It is too high for us.
How can ultrasound detect boundary a between media and the distances between them?
When a wave goes for one medium to another some it is reflected and some transmitted. This is called partial reflection.
If a pulse of ultrasound is put through an object boundaries can be found when some ultrasound is reflected back. The time it takes to reach a detector tells you how far away it is.
How can an oscilloscope be used to find boundaries?
Sharp spikes up and down are when a boundary is met.
Use the speed of sound and the time between boundaries to calculate distances.
However the distance calculated will have doubled as the sound is reflected there and back. Remember to divide by two.
How can ultrasound be used in medicine?
Ultrasound can be used to investigate blood flow, diagnose heart problems, check foetal development and destroy kidney stones.
How does ultrasound destroy kidney stones?
Kidney stones are masses that can block the urinalysis tract. High energy waves of ultrasound are concentrated at the stone and it turns to sand like particles which can leave in urine. His is very good as no surgery is needed and it’s relatively painless.
How can ultrasound be used to do pre-natal scans of a foetus?
Ultrasound waves pass through the body and can detect boundaries when they go between two boundaries. They can also calculate distance as the time they take to come back is measured. The information is processed by a computer to produce an image.
What are the pros and cons of using ultrasound?
They are non-ionising meaning they are safe to use.
However the images are fuzzy meaning it can be harder to diagnose conditions with them
What are the pros and cons of using X-rays?
They are ionising meaning they can cause cancer is too much is used and they can’t be used on a developing child.
However they produce clear images of bones and metal. Nothing elss.
What are the pros and cons of using CT scans?
They use a lot more radiation than normal X-rays meaning they are even less safe. They are only used when really needed.
However they produce detailed HD 3D images which means complicated illnesses and surgeries can be diagnosed and planed.
Explain refractive index.
Light will slow down when it goes into a new medium. This causes it to bend towards the normal. However sometimes some of the light will be reflected and it simply slows down if the light meets the medium at 90 degrees.
Define refractive index.
The ratio of speed of light in a vacuum to speed of light in medium.
What is the equation used to calculate refractive index?
Refractive index (n) = sin i divided by sin r
Reminder
Have a question of R I
What are the different types of lenses.
Converging and diverging.
Explain converging lenses.
Is it convex meaning it bulges outwards. It looks like a oval.
It causes parallel light rays to converge (move together ) at the principal focus.
Explain diverging lenses.
They are concave. They cave inwards causing parallel light to spread out.
The principle focus is the point where all the rays hitting the lens appear to come from. They all trace back and appear to have come from there.
Define focal length.
The distance between the centre of the lens and the principle focus.
