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88 Cards in this Set
- Front
- Back
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Who does IRR concern? |
Safety of staff and members of public. |
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Where does IRR stem from? |
Management of Healthy and Safety Work Regulations |
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What are the four main requirements of IRR? |
- Need to do prior risk assessment before do anything new with radiation - Need local rules and Radiation Protection Supervisor (RPS) - Controlled areas - Dose limits |
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Documentation which contains IRR? |
Approved Code of Practice |
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IRR - Reg 4 |
Duties of Employer |
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IRR - Reg 5+6 |
Authorisation and Notification of Work |
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IRR - Reg 7 |
Risk Assessment, Prior |
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IRR - Reg 8 |
Restriction of Exposure |
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IRR - Reg 9+10 |
PPE - look after |
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IRR - Reg 11 |
Dose Limitation |
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IRR - Reg 12 |
Contingency Plan |
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IRR - Reg 13 |
RPA |
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IRR - Reg 14 |
Instruction, Inform, Train |
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IRR - Reg 15 |
Co-operative Between Employers |
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IRR - Reg 16 |
Designation of Controlled Areas/Supervised Areas |
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IRR - Reg 17 |
Local Rules/ RPS |
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Who does IRMER concern? |
Patients |
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IRMER - what does a referrer do? |
-Registered Healthcare Professional -Can refer pt for medical exposure with a practitioner |
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IRMER - what does a practioner do? |
-Registered Healthcare Professional -Looks at all info given by referrer (i.e pt's condition, what's being taken a picture of) -Assesses if exposure is justified -Takes responsibility for exposure |
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IRMER - what does an operator do? |
Any person to carry out practical aspects of exposure. |
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IRMER - what must all clinical exposures be? |
Justified |
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What does ALARP stand for? |
As Low As Reasonably Practiceable |
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IRMER - whats a QA program? |
Ensures all equipment is working properly |
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IRMER - what does a lose dose lead to? |
Poor image quality |
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IRMER - DRLs (Diagnostic Reference Levels) |
-Examinations that must be set out by employers -Enables patient dose to be calculated |
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IRMER - which key things must be reported? |
-Training -Reporting incidents |
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What's a photon? |
A "packet" of energy - a single particle of light/x-ray (an x-ray is made up of many photons) |
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What can radiation be divided into? |
-Particle -Electromagnetic |
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Particle radiation is split into |
-Alpha -Beta |
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Describe alpha radiation |
-A helium nucleus with two protons and two neutrons. -Highly ionising -Stopped with a sheet of paper/few mm of air |
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Describe beta radiation |
-An electron -Ejected when a neutron converts to a proton -Has a -1 charge. -Highly ionising -Stopped by a few mm of aluminium |
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What does electromagnetic radiation consist of? |
Uncharged photons travelling at the speed of light |
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Gamma radiation |
- An excited nucleus can emit a gamma ray to return to its ground state (lowest energy state of the atom) -Has no charge -Less ionising -Requires lead to reduce its intensity -Same as x rays but produced by a different method |
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X rays can be generated in which ways? |
-Bremsstrahlung -Characteristic |
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Describe the Bremsstrahlung method |
-Electron passes near the nucleus and slows down -Its path is deflected -Electrons energy is released as a photon |
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Describe the Characteristic method |
-If an electron is ejected from an atom (due to collision with a free electron at high speed), will leave a gap in the energy level in which are orbiting -Space filled with another electron falling down from a higher energy level -As electron drops energy level, different in energy is released as a photon |
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Where does the production of xray occur? |
-In a high voltaged tube containing tungsten anode -Electrodes are accelerated towards it from a high temperature cathode filament -The anode is directed at the patient so the beams hits them |
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Describe the photoelectric efffect |
-When light is shone on an element and an electron is released -Due to a light photon colliding with an electron - and the energy which the photon had is passed to the electron -If this energy is greater than energy required to lift the electron to a higher energy level, then e- is released and known as a photoelectron. |
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Describe Compton scatter |
- Redirects photon - Photon has transferred some of its energy to the e- it collides with and scatters with less energy |
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Higher current means |
More photons, higher dose |
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Higher voltage means |
Less photons, less dose |
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What's the absorbed dose? |
Measure of radiation deposited in a unit mass of tissue, grays |
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What's the dose equivalent? |
Measure of absorbed dose weighted for harmfulness of different radiations, sieverts |
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What is effective dose? |
Dose equivalent for radiation susceptibility of different tissues, sieverts |
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Deterministic effects means |
When the effect is directly consequential of the dose above a certain threshold so below this threshold the consequence will not occur. |
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Stochastic effects means |
Effect will increase in likelihood but no minimum dose and the severity does not increase as dose increases. |
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Who is at higher risk of radiation? |
Younger children because tissues are dividng. |
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How does x rays cause genetic changes? |
-Interacts with DNA directly (electrons break DNA strand) -Or indirectly (electron leaves a trail of damaging OH free radicals behind) -Changes can be repaired so the cell returns to normal. Or unrepaired - cell dies/turns cancerous. |
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The longer you spend near a source of radiation |
The higher dose you receive |
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The dose and distance are |
Inversely proportional |
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What does shielding do? |
Attenuates radiation |
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What is the dose limit to whole body for staff and patients |
6mSV and 1mSV |
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What protects staff? |
-PPE -Constricted areas -Local rules |
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What are patients protected by? |
Aluminium |
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What are the general public protected by? |
-Room shielding -Exposure notes and signs |
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Describe the layers of a film |
Supercoat, emulsion, adhesive, base and backwards again. |
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What's the purpose of the coat? |
Transparent and protects emulsion |
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Describe the emulsion |
-Made of gelatine -Holds silver halide crystals -Allows film to flex whilst holding the crystals in place |
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Why do x-ray screens contain a phosphor layer? |
Converts the x-ray photon to a light photon which can interact with the film |
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The thicker the phosphor layer |
More chance photons will interact with film and create more light |
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The bigger the crystal size |
More blackening you get, so faster film but worse resolution |
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Latent Image Formation |
Silver deposits are produced in the film and larger areas of blackening form upon development due to Ag+ |
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Genetic stochastic effects |
DNA damage in reproductive cells may lead to congenital abnormalities/mental retardation |
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When would you use a bitewing? |
- When an offending tooth isn't obvious and want to screen for caries. -To look at bone levels - High caries risk - 6 monthly -Moderate - annually - Low risk - 12-18 months/2 years |
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When would you use a PA? |
- Offending tooth is obvious and TTP - Endodontic (ie working lengths) /PD lesion is suspected |
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When you would you use a cone beam? |
- Malignant sinus pathology - Implant planning |
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How would you improve image perception? |
- Get rid of background distractions - Reduce background illuminations - Magnification - Use a proper viewing box |
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What's the max photon energy set by? ie determines how much energy individual e- hav and therefore how much photon energy is released. |
Peak tube voltage (kVp) |
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What's filtration? |
- Anything we put between xrays made and patient being hit - Removes low energy radiation so intensity decreases and quality increases with filtration - Done with added sheets of metal |
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Transmission increases with |
kV but dose decreases |
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What has highest tissue weighting factors? |
Breast, bone marrow, colon, 0.12 |
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Bladder, oesophagus, gonads |
0.05 |
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Bone surface, skin, kidneys
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0.01 |
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Average annual UK background of radiation?
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2.5mSV |
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Digital radiographs are better in terms of |
- Storage, transport - Dynamic range of images - Digital processing |
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How do digital radiographs work? |
- Image first captured with a sensor (CR, CCD/CMOS) - Transformed into binary numbers |
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Computer radiographs - photostimulable phosphor |
Barium fluorhalide doped with europium - stored energy of xray photons and releases it as light |
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Digital radiographs - CCD/CMOS |
Use indirect conversion of the xray pattern into an electronic signal using a light omitting phosphor. |
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Resolution is highest in |
Film |
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Image quality is better in |
CR, CCD/CMOS |
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DICOM |
all modalities formatted to be recognised (dig im and comm in med) |
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RIS |
stores data regarding previous imaging investigations (rad inf system) |
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What happens as photons spread out from the interaction point? |
Causes a larger area of blackening therefore reduces the resolution of the system |
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Developer is |
An alkali and acts as a reducing agent (Ag+ to Ag) |
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Intermediate washing |
Stops developer working on the film |
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Fixing |
Acid, removes unreacted silver halide crystals |
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Final wash / Fixer solution |
Contains Ag and Br compounds must be remoed |
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Pros and cons of a small focal spot? |
Pros - less blurring Cons - higher density of e- hitting it and more heat so damage |
