Problems Associated with Scattered Radiation

Question 1

What is scattered radiation?

Answer 1

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

Question 2

Why is scattered radiation a problem?

Answer 2

Darkens image and decreases contrast.

Health and safety - could affect vets/nurses.

Question 3

Give 3 ways to minimise scattered radiation affecting the image

Answer 3

• 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)

Question 4

What are xray grids useful for?

Answer 4

Animals thicker than 10cm

Question 5

What are xray grids composed of?

Answer 5

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.

Question 6

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

Answer 6

Wobble the grid

Question 7

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

Answer 7

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

Question 8

Where is the grid usually located?

Answer 8

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

Question 9

WHat are the units of radiation exposure?

Answer 9

Roentgen

Question 10

What are the units of rate of radioactive decay?

Answer 10

Becquerel

Question 11

What are the units of absorbed dose of radiation?

Answer 11

Gray

Question 12

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

Answer 12

Sievert

Question 13

How are sieverts calculated?

Answer 13

Grays x Quality Factor (q.f).

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

Question 14

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

Answer 14

20mSv/year

Question 15

What two types of detector exist?

Answer 15

Film badge

Thermoluminescent detector

Question 16

What three ways can you minimise your exposure to radiation?

Answer 16

• 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

Question 17

Define the controlled area

Answer 17

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

Question 18

Define the designated radiation protection advisor

Answer 18

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

Question 19

Define the designated radiation protection supervisor

Answer 19

Monitors dosimeter readings and problems.

Question 20

What does ALARA stand for?

Answer 20

As low as reasonably acheivable