Diagnostic imaging (SA08) Flashcards
What are the dangers associated with radiography?
- X rays are invisible
- They are painless
- Effects are ‘latent’ (not seen immediately, may only be seen years later
- Effects are cumulative; repeated low exposures are as hazardous as a single large exposure
What are the principles of radiation protection?
- X rays must only be taken if definite clinical justification
- Exposure of personnel kept to minimum
- Time - reduce need for repeat exposures
- Distance - Stand 2 meters away
- Shielding - Wear PPE, stand behind lead screen
- No dose limit should be exceeded
What is the electromagnetic spectrum?
- Radiations with similar properties
- Low to high energy
- Radio waves, Microwaves, Infared radiation, Visible light, Ultraviolet, X-rays, Gamma-rays
What do all the waves of the electromagnetic spectrum have in common?
- Travel in waves
- Travel at same velocity
- Need no medium to travel, can pass through vacuum
- Travel in straight lines
- Interact with matter through absorption or scatter
What is the difference between radiowaves and x-rays?
RADIOWAVES
- Low energy radiation
- Low frequency
- Long wavelengths
X-RAYS
- High energy radiation
- High frequency
- Short wavelengths
How are x-rays different to other waves in the electromagnetic spectrum?
- Penetrate matter visible light can’t as high energy
- Interact with photographic film, produce latent image
- Interact with phosphor in intensifying screen to produce visible light (fluorescence)
- Interact with living tissues, produce bio changes
- Energy can be captured and converted to produce electronic images
What are the 3 types of x-ray machines?
- Portable
- Mobile
- Fixed
What are portable x-ray machines?
- Wall mounted or on portable stand
- Not very powerful
- Old machines only produce 20mA
- Newer machines can produce around 60mA
- kV and mA are usually linked, a given kV delivers a set mA
- Dental and equine
What are mobile x-ray machines?
- Large transformer box and trolly
- More powerful than portable machines
- Produce up to 300mA
- mA and kV can be set independently
- Machines in practice (often x-hospital)
What are fixed x-ray machines?
- Built in the room on overhead gantry/rails
- Needs special electricity supply
- Very powerful but more costly
- Often linked to floating tables
- Used in NHS
What is the x-ray beam made up of?
- Photons (packets of energy)
- Created when electrons are slowed down/stopped
- Electrons are present in atoms of all elements
What does the structure of an atom consist of?
- Protons (positively charged)
- Neutrons (no electrical charge)
- Electrons (negatively charged)
What does it mean for an atom to be electrically neutral?
- Equal number of protons and electrons
Where in an atom are the different elements?
- Protons + neutrons (centre of nucleus)
- Electrons orbit nucleus in shells
How are the charges of atoms changed?
- Changes to amount of electrons
- More protons than electrons, positively charged, Cation
- More electrons than protons, negatively charged, Anion
- Atomic numbers are number of protons in nucleus
- Important with how x-rays interact with different types of tissue and are seen on x-rays
What is needed for the on/off switch of a radiography machine?
- Must have warning light when machine on
- Now a ‘controlled area’, only radiography personnel allowed
- Often directly linked to lights outside room
- Should be isolator to turn off machine outside room in emergencies
What is a line voltage compensator?
- Ensures incoming voltage in consistent
- Produced by an autotransformer
- Built in part of modern machines
- Older machines may have indicator light
What are kilivolts (kV)?
- High power electrical charge
- Applied to target during exposure
- Draws electrons across
- Produced by a set up transformer
- ‘Penetrating power’
What are Milliamps (mA)?
- Low power electrical charge
- Heats filament
- Releases electrons during ‘prepping’ stage
- Produced by a step down transformer
- Number of electrons (quality)
What are seconds (S)?
- Timer for exposure time
- Some machines as low as 0.01 seconds
- Most exposures made at 0.05-0.5 seconds
What are the differences in old and new machines with inputting settings?
- Some modern machines automatically input settings from species, area and depth of patient
What are the 3 exposure factors?
kV
- Controls energy of photons
- Quality/penetrating power of primary beam
- Affects contrast and density of image
mA
- Controls number of photons
- Quantity/intensity of primary beam
- Affects density of image
s
- Controls number of photons
- Quantity/intensity of primary beam
What is mAs?
- mA x s
- Control number of photons per exposure
- mA = number of electrons emitted
- s = how long emission lasts for
