Radiography Flashcards
What are the 4 properties of x-rays that make them particularly dangerous?
- they are invisible
- they are cumulative, and their effects build up over time
- they are latent, and their effects are not immediately obvious
- they are painless
What are the two main effect types associated with x ray exposure?
Stochastic
Non stochastic (deterministic)
Describe stochastic effects of x rays
There is a random probability that these effects could occur. The likelihood of these effects increases with misuse of xrays and repeated exposure
What are some examples of stochastic x ray effects on the body?
The most significant is cancer development
Describe non-stochastic or deterministic effects of x rays
All other effects that are possible following exposure to x-radiation
What are some examples of deterministic effects of x rays?
- radiation induced skin burns
- acute radiation syndrome (radiation poisoning)
- cataracts
- anaemia
- sterility
- DNA mutations
According to the HSE, what must exposure to x-radiation be?
ALARP - as low as reasonably practicable
Describe somatic effects of x radiation
Damage from x radiation that becomes apparent during the affected individuals lifetime. It is deterministic.
Examples include skin burns, cataracts, infertility
Describe genetic and teratogenic effects of radiation
Deterministic.
Inheritable changes, and potentially mutations in DNA. These may not affect the individual but can affect their children or even grandchildren
What are some examples of genetic and teratogenic damage by x radiation?
- chromosome changes
- stillbirths
- congenital abnormalities
- infant and childhood mortality
- malformations and teratomas
Define a TERATOGEN
Substances that cause congenital disorders in a developing embryo or fetus.
It is anything that a person who is pregnant is exposed to or ingests while they are pregnant that is known to cause fetal abnormalities
Define a TERATOMA
A tumour made up of several different types of tissue, such as hair, muscle, teeth, or bone. Typically form in the ovary, tailbone, and testicle
Describe the carcinogenic effects of x radiation
This is a stochastic effect. These concern the introduction of cancers in tissues that have been exposed to radiation. Often this is the effect of latent, cumulative exposure e.g. leukaemia
Define a CARCINOGEN
Something that causes cancers
What are the three basic principles of protection from radiation?
- use of radiation must have clear clinical justification (must be for diagnostic purposes, not a shot in the dark)
- any exposure of personnel should be kept to an absolute minimum. This can be aided by correct technique, and correct use of chemical restraints to reduce the need for repeat exposures
- no dose limit should be exceeded, and dosimeters should always be correctly used
What amount do veterinary practices have to pay under the IRR (2017)?
They have to register as medium risk workplaces and pay a fee of £25
What is some of the legislation that regulates the use of x radiation?
- the Ionising Radiation Regulations (2017)
- local radiation rules and regulations
- the Health and Safety at Work Act (1974)
- Controlled Waste Regulations (2012)
-Control of Substances Hazardous to Health (2002)
What different groups of people do x radiation dose limits apply to?
- radiation workers who are over 18 years old
- trainees who are under 18 years old
- other persons
- women of reproductive capacity
What is the dose limit rate for radiation workers who are older than 18?
20 mSv in any calendar year
What is the dose limit rate for trainees who are under 18?
6 mSv in any calendar year
What is the dose limit rate for other persons?
1 mSv in any calendar year
What is the dose limit rate for women of reproductive capacity?
13 mSv in any consecutive period of 3 months
Once a pregnancy has been confirmed and reported to the employer, the dose rate should not exceed 1mSv for the remainder of the pregnancy
When should a pregnant member of staff inform their employer?
As soon as they have a pregnancy diagnosis - risk assessments should be carried out for pregnant and breast feeding employees
Who are the people who have direct control over x radiation in practice?
Radiation Protection Supervisors
Radiation Protection Advisors
Designated Radiographers
What is the Radiation Protection Supervisor?
An authorised person who works in practice. They are responsible for enforcing safe practice and promoting the local rules and scheme of work. They work under the external RPA
What is the Radiation Protection Advisor?
Someone external to the practice. They are competent in advising employers on the safe and compliant use of ionising radiations. It is a requirement under the IRR (2017), and may be a human radiographer, or senior vet. They visit the practice once a year
Who are the designated radiographers?
These are members of practice who have had specific training in the safe use of x-rays, and how to use the equipment. They must be on the list of designated radiographers that should be visible outside the x ray room and their own dosimeter
What are the local rules?
A set of instructions for correct use of the x radiation equipment drawn up by the RPA. They set down:
- equipment details
- procedure and restriction of the controlled area
- methods of restraint
- precautions for manual restraint
- assessment of max dose likely to be received by staff
- the written scheme of work, which details step by step procedures for the radiographer
What is the controlled area?
The controlled area is 2m from the tube head. Nothing should be in this area apart from the patient.
A controlled area must be present if the x ray dose exceeds 7.5mSv per hour, or if any one person is expected to receive more than 6 mSv per year
What should warning lights for x rays indicate?
- when the machine is on
- when x rays are being produced
There should also be an audible beep
Who is responsible for ensuring x ray machine are working correctly?
The manufacturers of the machines - it is a legal requirement that x ray machines are serviced by engineers at least once a year
What groups of people should not carry out x rays?
Pregnant people, those under 16, and members of the public
Where should dosimeters be worn?
In practice only. They should be worn at all times during radiographic procedures
Where should dosimeters be kept?
Outside the x ray room, and out of direct sunlight. They pick up on all kinds of radiation, so should not be stored near microwaves or radios.
What are the two types of dosimeters?
- film badges
- thermoluminescent dosimeters
Describe film badge dosimeters
Contain a small amount of metal x ray film which determines the level of radiation exposed to
Describe thermoluminescent dosimeters
More modern than film badges. They contain radiation sensitive lithium fluoride crystals and are usually orange. The crystals change atomically when exposed to radiation
How long should records from xrays be kept?
50 years!
What different types of PPE are used for x rays?
Lead aprons, lead gloves and lead thyroid/neck protectors
How should a lead apron be stored?
Hanging up, or lying flat. It should never be folded as it could crack the lead
What is the minimum thickness for a lead apron?
0.25mm
What is the minimum thickness for lead gloves?
0.35mm
What is the minimum thickness for neck/thyroid protector?
0.35mm
What is important to remember about lead lined gloves?
They will not protect the operator from the primary x ray beam
Define WAVELENGTH
The measurement between two peaks or two troughs of an electromagnetic wave
Define FREQUENCY
Considers how many peaks and troughs occur in a specific unit of time
What are the common features of the members of the electromagnetic spectrum?
- don’t require a medium for transmission
- all travel in straight lines
- all travel at the same speed
- all interact with matter (may be to absorb or to scatter)
What are the additional features of x rays that mean they are particularly good for imaging?
- their penetration ability
- latent images can be made visible by processing
- they fluoresce
- they produce biological changes in living tissue (used in radiotherapy)
Define NEOPLASIA
Uncontrolled abnormal growth of cells or tissues within the body
Define QUANTA
A discrete quantity of energy proportional in magnitude to the frequency of the radiation it represents (small packets of radiation energy)
Define an ELECTRON
A negatively charged subatomic particle
Define a PROTON
A positive subatomic particle
Define a NEUTRON
A neutral subatomic particle
What is the process of x-rays being produced?
X-rays are produced within the tube head of the machine. The electrons are fired at the target, they are stopped or slowed down which release photons of x rays. If an electron is stopped, it gives up all its kinetic energy and the resulting x rays have high energy
Define a PHOTON
An elementary particle that is a quantum of the electromagnetic field. Photons are called ‘x-rays’ if they are produced by electron interactions
Define KINETIC ENERGY
Energy which the object has by virtue of being in motion
What happens if an electron is slowed down?
It produces x ray quantas of variable energies - x radiation are said to be polychromatic for this reason
Define POLYCHROMATIC
Literally means ‘many coloured’. In the context of x rays it means differing energies
How are x rays produced?
- slowing down or stopping the electron (Bremsstrahlung)
- removing an inner electron. As the electron is replaced, photons are emitted
What is the wavelength of an x ray photon?
0.01-10 nanometers
What is the tube head of an x ray machine?
The place where x rays are produced. The rest of the x ray machine is involved in the transformation of the electric current
What are the components of the x ray tube head?
The cathode, the anode, the filament, the glass window, the target, and the focusing cup
Define FILAMENT
A conducting wire or thread with a high melting point forming part of an electric bulb or thermionic valve, heated or incandescent by an electric current
Usually made of tungsten
Define THERMIONIC EMISSION
Liberation of electrons from an electrode by virtue of its temperature
What percentage of electrons produce x ray photons?
Only around 1% of electrons produce x ray photons; the rest are lost in heating up the target
What are x ray filaments and targets usually made from and why?
It has a high atomic number (74), meaning it has many electrons in its outer shells. It also has a high melting point of 3380 degrees Celsius
What is the process of x rays being created?
- The tube current (measured in mAs) is passed over the filament. This causes it to heat and release electrons (thermionic emission)
- The voltage is applied across both the anode and the cathode, creating a potential difference. This motivates the electrons to move, giving them kinetic energy
- The electrons are stopped or slowed down when they hit the target. Around 1% are released as x rays and the rest as heat
Is the anode positive or negative?
Positive. It sits in a vacuum with the cathode. Together they make up both sides of the x ray tube head
Is the cathode positive or negative?
Negative. It sits in a vacuum with the anode. Together they make up both sides of the x ray tube head
What are the two types of anode?
Rotating and stationary
Describe stationary anodes
The simplest type of anode, very stable. The heat hits the target in one place, causing wear. Photons are shot out unevenly and the target can be quickly worn down. They are difficult to change once damaged and are usually found in portable or x ray machines
Describe rotating anodes
Has a large target area - the anode rotates and heat is not just applied to one area. Any machine that has high kV and mAs capabilities will have a rotating anode; usually found in large machines
What is the use of oil within the tube head?
Used for cooling both the anode and cathode to prevent overheating
What are the exposure factors?
kV and mAs
Describe the kV (kilovoltage)
This is the potential difference which is applied across the tube head during the instant of exposure. It determines the energy/speed the electrons have and therefore the energy they have to lose when they hit the target.
Also determines the penetrating power, type of interaction in the body and level of scatter
What are higher kVs requires for?
High density anatomy, such as bone and abdominal tissue. Helpful to reduce movement blur for certain anatomy (e.g. heart/lungs)
What does kV affect?
Contrast (the greyscale of the image)
Radiographic density (blackening of the film/image)
What is the milliamperage?
The measure of the number of electrons crossing the tuber head at the instant of exposure. The amperage defines the degree of heating of the cathode filament and therefore the number of electrons released during thermionic emission. Does not affect penetrating power
Combined with the timer it creates mAs (milliamperes per second)
What is the use of the timer in x rays?
Determines the length of exposure, combined with milliamperes it creates mAs.
High mAs can be achieved with either high mA, or longer exposure
What is the effect of longer exposure?
Increased risk of scatter and movement blur. This results in the need for repeat x rays which contravenes the HSE’s ALARP policy
What does the degree of x ray absorption into matter depend on?
- The atomic number (number of protons)
- The atomic weight (number of neutrons and protons)
- The effective atomic weight - the average number of molecules in the tissue
- The specific gravity of the tissue - the density of mass per unit
What colour does metal appear when x rayed?
White. For example the left and right markers for labelling x rays
What colour does gas appear when x rayed?
Black
Describe scatter
May be external - bounces around the designated area and pose a health and safety hazard.
May be internal - affects the x ray film and disturbs the images contrast and definition
What are some methods of reducing scatter?
- good collimation. Use of grids can aid this
- use of a lead topped table
- use of exposure charts
- compression of large areas of soft tissue
- reduction of kV where possible
What causes scatter to increase?
- increased kV
- increased mAs
- thicker, denser tissue (anything with a thickness greater than 10cm requires a grid)
What are the two types of scatter?
Compton scatter and coherent scatter
Describe coherent scatter
Also called Raleigh or classical scattering
This type of scatter occurs within the patient - it is a change in the direction of the incident x ray without a change in its energy
Describe Compton scatter
Results in ionisation of the target atom, reduction in the energy and a change in the direction of the photon, can create a health and safety hazard
What is the relationship between the mAs and kV dose?
For every 10kV increase, the mAs can be halved. Always work with the highest kV possible and the lowest mAs.
What does decreased kV lead to?
Leads to an increase in photoelectric absorption (more absorption by denser and thicker tissues). Produces images that are too light
What does increased kV lead to?
Leads to a decrease in photoelectric absorption, so everything is absorbed. Produces images that are too dark. Increases Compton scatter
What is Sante’s rule?
This rule is no longer use but is good to know
It is used to establish the initial kV when producing an exposure chart, using a cooperative dog and several exposures. Not safe or ALARP, no longer done
What is the x ray tube rating?
The maximum kV and mAs that are produced by an x ray machine are determined by the amount of heat it can withstand. Exceeding these limits can cause the machine to become overheated, although most modern machines have safety features to prevent overloading
What must be recorded for each x ray taken?
- patient ID
- person taking the x rays
- position and anatomy
- exposure settings
- number of x rays taken
- quality of x rays
- date of x rays
What is the radiographic latitude?
A measure of the range of exposures that will result in a radiographic density within the diagnostic range. The wider the latitude, the greater range of object densities visualised
What is the film focal distance?
The distance from the focal spot (target). It should not be able to be changed for health and safety reasons, and due to the change in image quality
What is penumbra?
The further away from the source the film/patient is, the less sharp the image will be
What is umbra?
The opposite of the penumbra effect
What is the inverse square law in relation to film focal distance?
The intensity of the primary beam projected onto an x ray film is reduced by one quarter by doubling the distance from the x ray film
What is the typical FFD for portable x ray machines?
75cm
What is the typical FFD for fixed x ray machines?
100cm
