X Rays And Ecgs Flashcards
What is thermionic emission
a filament acts as a cathode it is heated to give more to its electrons once they have enough energy they escape
They’re then accelerated towards the anode by a potential difference between the cathode and anode
When the electron collides with the anode some kinetic energy is converted into X-rays
The reaction takes place inside a gas tube with a vacuum
Lead casing is put around the tube to absorb some of the X-rays so they’re only aimed at thing in question
Kinetic energy of each electron (in joules)
Electronic charge (in coulombs) X accelerating potential difference (in volts)
Current (amperes) =
Number of particles per second X charge on each particle (coulombs)
How do x rays harm the body’s cells
They have high frequency and high energy
They can remove electrons from molecules in living cells
This means the cells are damaged or destroyed which can lead to tissue damage or cancer
What is an inverse square relationship
If you move twice as far away from the source the same radiation is spread over four times the area
How does the thickness of a material affect X-ray absorption
The more dense the material the more x rays absorbed
Also the thicker the material the more X-rays are absorbed
Lead and concrete are used to reduce people’s exposure to X-rays in hospitals
What is X-ray tube casing
X-ray tubes have an outer case used to absorb X-rays
The thicker the material the greater the reduction in X-ray intensity
What is X-ray fluroscopy
Placing a patient between an X-ray source and a fluorescent screen
Different amount of X-rays are absorbed as they pass through the patients body
The X-rays then hit a fluorescent screen which gives a live image of the patient
The higher the intensity of the X-ray the brighter the screen
There is a machine which intensifies the fluorescent so a lower intensity of X-rays can be used
The screen is attached to a computer so images can be recorded
What is fluoroscopy used for
To diagnose problems with organs and they way they function e.g. To look at blood flow or movement through the gastrointestinal tract
X-rays pass easily through soft tissue so the patient is given a contrast medium by injection or ingestion which improves the quality of the image produced by enhancing the soft tissue
What do cat scans do
An x ray beam rotates around the body and is picked up by thousands of detectors
A computer works out how many of the X-rays are absorbed and produces a very high quality image
They can show 3D images by stacking individual 2D slices
They are often used to look for cancer and Tumors
What are the risks of using X-rays for imaging
They can be harmful to us because they’re ionising
What are the advantages of using X-ray imagining
They can diagnose injury well so there’s no risk of giving the wrong treatment
Hospitals limit X-ray exposure
It is quick and not invasive
The quality of the images produced is much better than other methods such as ultrasound
What is an action potential
When a muscle cell is stimulated by an electrical signal the potential difference changes this potential passes down the cell making the muscle cell contract
Why can muscle cells generate potential differences
Between the inside of the muscle cell and the outside there is a voltage at rest this is called the rest potential
This can be measured using tiny needle electrodes it’s about -70mV
What happens when the heart beats
An action potential passes through the atriums making them contract then a few milliseconds later another action potential passes through the ventricles making them contract too
Once the action potential has passed the muscle relaxes
