11704646
Description
Flashcards by Rachael Jones, updated more than 1 year ago
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Created by Rachael Jones
over 6 years ago
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| Question | Answer |
| Give 2 ways to reduce the effects of scattered radiation on the X-ray image. | - Grids - Tighter collimation |
| How are grids used? | • Used in conjunction with X-ray cassettes when radiographing thick objects (>10cm) to reduce the amount of scatter radiation reaching the film |
| What is the result of using grids? | Improve the image quality |
| What are grids? | • Flat plates • Series of thin lead strips alternating with thin plastic strips • The lead strips are designed to absorb most of the scattered radiation, which impinges on the grid from all directions • The plastic strips are designed to allow the primary beam through (radiolucent) |
| What can vary from grid to grid? | The orientation of the strips, their height and number of strips per centimetre |
| What is grid ratio? | - The height of the lead strips divided by the width of the spacing material - 6:1 means that the height is 6 times the width of the spacer |
| How is grid ratio used to remove scatter? | The higher the ratio the more efficient at removing scatter but it also removes a greater proportion of the primary beam so higher exposure required (increase mA) |
| What is the most common grid ratio? | 6:1 or 8:1 |
| What is lines per centimetre? | - The more lead strips there are per cm the more scatter is removed, but greater exposure required (increase mA) - greater proportion of primary beam removed |
| What is grid factor? | - Number quoted by the manufacturer - Relates the grid ration and lines per cm - Commonly 2.5 to 3 - Necessary to increase exposure factors (mAs) when using grid - The number by which the mAs must be multiplied if a grid is used |
| What are the 4 types of grid? | • Parallel • Focussed • Pseudofocussed • Potter-Bucky (moving) |
| What are features of parallel grids? | - Lead strips all of same height and parallel to each other - Increased absorption of the primary beam towards the edges of the grid (grid "cut-off”) - Centering of the beam to the grid is not critical as long as the direction of the beam is perpendicular to the grid (parallel to the strips) |
| What are features of focused grids? | • Lead strips are angled to accommodate the divergence of the X-ray beam • Grid "cut-off" does not occur • Centering of the X-ray beam to the centre of the grid and the use of the correct film-focal distance are critical • The grid must not be used upside down |
| What are features of Pseudo-focussed grid? | • Parallel lead strips but their height progressively decreases towards the edge of the grid to reduce the "cut-off" effect • Compromise between parallel and focused grid |
| What are features of Potter-Bucky grids? | • Parallel grids mounted between the table top and the cassette tray of purpose built X ray tables. • When an exposure is made, the grid moves from side to side to blur out the grid lines |
| What is collimation? | Restriction of the area covered by the primary X ray beam |
| How is collimation usually achieved? | By a Light Beam Diaphragm |
| How does the light beam diaphragm work? | - A light bulb and series of mirrors produce a beam of light which will outline the path of the x ray beam - Allows operator to see effect of opening and closing the shutters and to adjust as necessary |
| How is the light beam diaphragm adjusted? | So that only the area of interest is exposed by the X-rays |
| What is the main advantage of collimation? | Parts of body are not unnecessarily exposed to radiation - primary beam should not exceed that of the film/digital image detector |
| What is the overall effect of collimation? | Volume of tissue irradiated is minimised, then quantity of scattered radiation produced is also minimised - improving image quality |
| What are the hazards of radiation? | • Ionising radiation is harmful to living tissues • The nature of any damage will depend on the tissue irradiated, the characteristics of the radiation, the dose of radiation received and the time period of exposure • Doses of radiation are cumulative • Rapidly dividing cells are most susceptible to the effects of ionising radiation |
| What are the potential results of radiation? | • Inflammation, slowed cell growth, necrosis • Potential malignant change • Genetic mutation |
| What is the ALARA principle? | • Keep doses of radiation to patients and personnel As Low As Reasonably Achievable |
| What are the methods of protection from radiation? | - Space/ distance - Barriers - Protective clothing - Time |
| How can space work to protect? | - X-rays attenuated by distance (inverse square law) - Keep as far away from the primary beam as possible |
| How can barriers be used as protection? | - Most stone or brick walls will stop scattered radiation but not primary beam - Lead or barium into plaster or cavity (double thickness) is required to stop primary beam - Consider for horizontal x-ray beams |
| How is protective clothing used as protection? | - Lead aprons and gloves - Protective clothing offers protection only against scattered radiation, not the primary beam |
| How can time be used as a form of protection? | - Reducing the time spent exposed to radiation reduces the dose • Shortening examination times in certain procedures (scintigraphy, fluoroscopy) will reduce doses to personnel |
| Should any part of an assistant ever be allowed to be exposed to the primary beam? | NO - NEVER |
| What are the legislation surrounding the use of radiation? | • Ionising Radiations Regulations 1985 and 1999 -> Being updated next year (IRR17) • BVA Guidance notes for the safe use of ionising radiations in veterinary practice 2002 |
| What should every practice have that works with ionising radiation? | ‘Local Rules’ in place • Detail specific information about personnel and working practices |
| What 2 people need to be appointed by a practice working with ionising radiation? | • Radiation protection advisor (external) • Radiation protection supervisor (internal) |
| What does the RPS do? | - Within practice - responsible for ensuring that all work is carried out safly |
| What does the RPA do? | - External - helps set up the system and works with RPA |
| What are the restrictions on the controlled area? | • Where the radiation dose may exceed 7.5µSv/hour • 2m around a vertical beam • Designation and restriction of access (lights and signs) |
| What should the Local Rules have details of? | • X-ray Equipment • Servicing Arrangements • Personal Protective Equipment • Personal Dosimetry • Contingency Plan • Record Keeping |
| What should be done for restricting an animal during X-ray? | - Use sand bags, ties and foam for small animals - No animal should be manually restricted except in exceptional clinical circumstances (horses) |
| What must anyone who does stay in the room wear? | Wear protective clothing and stand as far from the primary beam as possible |
| Are humans allowed to be in the X-ray even with protective clothing on? | No |
| What can be placed under the X-ray cassette to absorb radiation from a vertical beam? | Sheet of lead |
| Who should never be involved in radiography? | Nobody who is under 16 years old or who may be pregnant |
| Why are Personal dosimeters worn? | • To monitor that the procedures are working • To monitor that personnel are receiving minimal doses of radiation |
| What are features of Personal Dosimeters? | • Individual use • Change regularly (3 monthly) • Wear UNDER any protective clothing • Store carefully -> washing machine, airports… • Document any potential doses and issue another monitor |
| What are the legal dose limits? | • General Public 1mSv • Trainees (16-18) 6 mSv • Occupational (18+) 20 mSv - Can’t exceed 3/10 of these limits without becoming a ‘classified’ worker |
| What can happen if you take a radiograph of a person, even with permission? | Prosecuted |
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