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Flashcards in Problems Associated with Scattered Radiation Deck (20)
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1
Q

What is scattered radiation?

A

Xrays that have been deflected from the primary beam by an interaction with matter (patient/table top etc.)

2
Q

Why is scattered radiation a problem?

A

Darkens image and decreases contrast.

Health and safety - could affect vets/nurses.

3
Q

Give 3 ways to minimise scattered radiation affecting the image

A
  • Minimise volume of tissue being irradiated - collimate with light beam diaphragm
  • Lead rubber between casette and table top
  • Use ^kVp exposure with vmAS (use less xrays to get the same result)
4
Q

What are xray grids useful for?

A

Animals thicker than 10cm

5
Q

What are xray grids composed of?

A
Lead strips (24/cm) then aluminium or plastic inbetween.
Scattered radiation comes in at an angle and is absorbed, only radiation from the primary beam fits smoothly through.
6
Q

How do you prevent the lead lines showing up on a radiograph?

A

Wobble the grid

7
Q

How else must the exposure be compensated when using a grid?

A

Increased the amount of radiation (mA) to compensate for xrays absorbed - called the grid factor
Usually 2-3x normal

8
Q

Where is the grid usually located?

A

Within the table. Move cassette under table to make use of grid/

9
Q

WHat are the units of radiation exposure?

A

Roentgen

10
Q

What are the units of rate of radioactive decay?

A

Becquerel

11
Q

What are the units of absorbed dose of radiation?

A

Gray

12
Q

What are the units of dose-equivalent measure of effect of radiation

A

Sievert

13
Q

How are sieverts calculated?

A

Grays x Quality Factor (q.f).

Quality factor = 1 for gamma and xrays, for more ionising radiation is higher

14
Q

What is the MPD (maximum permissable dose) for persons at work 18 years +

A

20mSv/year

15
Q

What two types of detector exist?

A

Film badge

Thermoluminescent detector

16
Q

What three ways can you minimise your exposure to radiation?

A
  • Time: minimum time spent in contact with xrays by only taking them when clinically relevent and minimising retakes
  • Distance: keep away from patient (source of scatter)
  • Barriers: Personal - lead apron/gloves
    Mobile - Lead plywood doors
    Walls - Brick/leadsheet/barium plaster
17
Q

Define the controlled area

A

Area around the primary beam within which the average radiation dose rate exceeds the permissable limit
Typically 2mx2m OR the radiography room
Warning signs necessary

18
Q

Define the designated radiation protection advisor

A

Someone named in the local rules as permitted to inspect and advise on safe radiographic practices, provide local rules and define controlled area.

19
Q

Define the designated radiation protection supervisor

A

Monitors dosimeter readings and problems.

20
Q

What does ALARA stand for?

A

As low as reasonably acheivable