Karteikarten
Principles of diagnostic imaging 2 - KB
Karten in diesem Stapel (46)
- 1Give 2 ways to reduce the effects of scattered radiation on the X-ray image.- Grids
- Tighter collimation - 2How 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 - 3What is the result of using grids?Improve the image quality
- 4What 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) - 5What can vary from grid to grid?The orientation of the strips, their height and number of strips per centimetre
- 6What 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 - 7How 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)
- 8What is the most common grid ratio?6:1 or 8:1
- 9What 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
- 10What 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 - 11What are the 4 types of grid?• Parallel
• Focussed
• Pseudofocussed
• Potter-Bucky (moving) - 12What 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) - 13What 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 - 14What 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 - 15What 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 - 16What is collimation?Restriction of the area covered by the primary X ray beam
- 17How is collimation usually achieved?By a Light Beam Diaphragm
- 18How 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 - 19How is the light beam diaphragm adjusted?So that only the area of interest is exposed by the X-rays
- 20What 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
- 21What is the overall effect of collimation?Volume of tissue irradiated is minimised, then quantity of scattered radiation produced is also minimised - improving image quality
- 22What 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 - 23What are the potential results of radiation?• Inflammation, slowed cell growth, necrosis
• Potential malignant change
• Genetic mutation - 24What is the ALARA principle?• Keep doses of radiation to patients and
personnel
As Low As Reasonably Achievable - 25What are the methods of protection from radiation?- Space/ distance
- Barriers
- Protective clothing
- Time - 26How can space work to protect?- X-rays attenuated by distance (inverse square law)
- Keep as far away from the primary beam
as possible - 27How 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 - 28How is protective clothing used as protection?- Lead aprons and gloves
- Protective clothing offers protection only against scattered radiation, not the primary beam - 29How 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 - 30Should any part of an assistant ever be allowed to be exposed to the primary beam?NO - NEVER
- 31What 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 - 32What should every practice have that works with ionising radiation?‘Local Rules’ in place
• Detail specific information about personnel and working practices - 33What 2 people need to be appointed by a practice working with ionising radiation?• Radiation protection advisor (external)
• Radiation protection supervisor (internal) - 34What does the RPS do?- Within practice - responsible for ensuring that all work is carried out safly
- 35What does the RPA do?- External - helps set up the system and works with RPA
- 36What 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) - 37What should the Local Rules have details of?• X-ray Equipment
• Servicing Arrangements
• Personal Protective Equipment
• Personal Dosimetry
• Contingency Plan
• Record Keeping - 38What 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) - 39What must anyone who does stay in the room wear?Wear protective clothing and stand as
far from the primary beam as possible - 40Are humans allowed to be in the X-ray even with protective clothing on?No
- 41What can be placed under the X-ray cassette to absorb radiation from a vertical beam?Sheet of lead
- 42Who should never be involved in radiography?Nobody who is under 16 years old or who
may be pregnant - 43Why are Personal dosimeters worn?• To monitor that the procedures are working
• To monitor that personnel are receiving
minimal doses of radiation - 44What 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 - 45What 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 - 46What can happen if you take a radiograph of a person, even with permission?Prosecuted
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- Foundations of clinical veterinary science - CVS1 (Diagnostic imaging - Kate Bradley) Karteikarten am Principles of diagnostic imaging 2 - KB, erstellt von Rachael Jones am 07/12/2017.
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