Exposure & Radiation Safety Flashcards
Discuss the relevance of ORS C1
The Code of Practice for Diagnostic and Interventional Radiology (ORS C1) is issued by the Director for Radiation Safety of the Radiation Safety Act.
We must practice in accordance to ORS C1 which covers radiation protection and safe practice in regards to - 3 radiation principles Dose limits Personnel monitoring Protection of personnel and patients Xray equipment QA programmes.
When may you get grid cut off when performing a horiray hip?
What type of grids to we have here at the nelson hospital? State -
bucky factor
grid ratio
grid frequency
If the grid is not properly aligned.
If the grid lines are running horizontally and the gird is tilted backwards or forwards
If the grid is placed back to front.
We use parallel grids in Nelson, that have a bucky factor of 4, grid ratio of 10:1 and grid frequency of 85 per unit.
Discuss the relevance of Electrical Safety act
MRTs must attend annual electrical safety meetings.
Equipment and appliances used in the hospital must be approved and have grounded plugs.
All electrical outlets must be regularly inspected. And problems reported.
ALARA -
What is it
How can we use it to reduce dose
As low as reasonably achievable.
Dose should be ALARA to get diagnostic image.
We can reduce dose by - Collimation Increasing kVp Using lead shielding Increasing FFD JLO Lower repeats and number of images
What are the dose limits of -
MITs
Public
Patients
MRTS -
Whole body effective dose of 20 mSv per year over 5 year period. Max of 50 mSv in any one year.
Patient -
No legal limits, as long as benefits outweigh the risks.
Public -
Whole body effective dose of 1 mSv in any one year.
Discuss the principles & practices of radiation protection
PRINCIPLES -
Justification - risk vs benefit
Limitation - accumulation of dose over time should not exceed guidelines
Optimisation - ALARA
PRACTICES -
Shielding - from primary and secondary beam
Time - limit
Distance - inverse square law
How do you know if you have a good kVp/mAs?
How do you know to adjust the mAs or kVp if your image is under or over exposed?
With adequate mAs - trabecular pattern of bone demonstrated as well as soft tissue structures.
With adequate kVp, bony cortical outlines are clearly visualised and the contrast scale is acceptable.
In practice usually an adjustment of both. You can be guided by the cortical outlines of bony structures. For example, if the cortical outlines are visualised but the density is too light, your image is likely to be under exposed with mAs.
However, if cortical outlines of thicker structures are not visualised you image will be underpenetrated - too little kVp.
What is the difference between kVp and mAs
kVp - the quality of the beam, describes the penetrating power of the beam. It is the energy of the beam produced by voltage. Penetration and radiographic contrast are regulated by kVp.
mAs - the quantity of the beam (number of electrons in the beam.) The intensity of the beam. Produced by current, radiographic density regulated by mAs. Best to keep mA high and s shorter to reduce chance of patient movement.
What are some technical factors which you consider when setting an exposure?
Patient - size state - clothes mobility - breathing abiltiy history whats being xrayed? ST or skeletal
Equipment - bucky or not grid or not collimation filters radiation protection sponges lead rubber FFD
Technique -
AP/PA
lateral
CM used
Choices -
kV
mA
Times
