Lecture 2 - X radiation science and technology Flashcards
The discovery of X-ray Principles of radiography Xray equipment Xrays: what they are and how they are produced Xray tube: cathode, filament, focusing cup, anode, target
When was X-ray discovered?
In 1895 by Wilhelm Roentgen
Is photon absorption by the patient more likely at high or low energies?
Low energies
Why is bone more absorbing of X-rays than soft tissue for example?
It has a higher density and atomic number
Does higher absorption appear more black or white on the X-ray film?
More white (less photons hitting the image receptor).
Lower absorption therefore appears more black as more photons hit the image receptor.
This allows an image to be produced according to the different absorptions by different anatomy
What are the four types of behaviour X-rays exhibit when they pass through the patient?
Pass through the patient reaching the image receptor
Absorbed by the patient
Scattered
Transmitted
How are X-rays produced?
Cathode (-ve) produces high speed electrons as a result of heating from a high current generator
These electrons are directed toward the anode (+ve), which spins in order to maintain cooling. Here electrons are converted into X-rays by rapid deceleration and loss of energy which is given off as X-rays.
What key properties of an X-ray tube are important for its functionality in a clinical setting?
Mobility - enables X-rays to be taken in various situations, angles and positions
Uniformity - X-rays produced are of uniform energy to provide image contrast
Collimation - the beam can be adjusted in order to change its size/area to enable imaging of different sized body parts
What is collimation and why is it important?
Adjusting the size of the X-ray beam for imaging different size body parts.
This must be set for optimal image quality and minimal dose to the patient.
(Larger area image required for abdo vs hand but also means larger radiation dose to patient and more scatter = lower image qual)
What two factors can be adjusted by the radiographer in order to control image appearance?
kVp - X-ray energy
mAs - Amount of X-rays
What is kVp?
Peak kilo voltage. Amount of energy the X-ray has which is increased by a greater potential difference between the cathode and anode.
What relationship does kVp have to image contrast?
Higher kVp = lower contrast of X-ray image
A higher kVp would be required for an area with higher subject contrast such as chest in comparison to abdomen.
What is mAs?
milliamps/second. Amount of X-rays produced by X-ray tube per exposure length of time.
With thicker tissue doe you have to increase or decrease mAs?
Increase.
More X-rays will be absorbed by the patient if they have thicker tissue e.g. overweight, so in order ti have enough X-rays pass through and impact on the image receptor, mAs must be increased.
What is image centring and why is it important?
Where the central photon is.
Across the width of the beam, X-rays diverge and the only one that is directly perpendicular to the exit tube is the central ray.
Alignment of this is important in order to minimise extortion and magnification of the anatomy.
What is the purpose of an anti scatter grid and how does it work?
Works like polarising lenses - grid prevents photons that aren’t travelling in the correct direction from passing through, so they don’t hit the image receptor and cause scatter. This improves the quality of the image.
