Radiographic safety

Question 1

X-rays are a form of what type of radiation?

Answer 1

Electromagnetic

Question 2

On the electromagnetic spectrum what type of wavelength and frequency do x-rays have?

Answer 2

Short wavelength and high frequency

- inversely proportional to each other

Question 3

What makes x-rays damaging to tissues?

Answer 3

High energy - able to produce ionisation

Question 4

X-ray photons are produced when high speed electrons hit what metal target? Describe how this happens.

Answer 4

Anode

- the electrons are produced at the cathode and are accelerated by potential difference

Question 5

Why is the process of x-ray production inefficient?

Answer 5

Lots of energy is released as heat

Question 6

What controls the size and shape of the primary beam?

Answer 6

Lead collimators

Question 7

What are the 3 tube variables that the radiographer can alter?

Answer 7

1. kilovolt peak (kVp) - potential difference between anode and cathode
2. milliamps (mA) - number of electrons accelerated
3. seconds - length of exposure

Question 8

What is the anode made from?

Answer 8

A bevelled rotating disc of tungsten

Question 9

What is penumbra? how can it be reduced?

Answer 9

Blurring at the edge of structures

- reduced by having a smaller effective focal spot

Question 10

How can the size of a focal spot be decreased?

Answer 10

Decreasing width of electron beam that is hitting the anode

Decreasing the angle of the anode

Question 11

What is the purpose of placing an aluminium filter in the path of the primary beam?

Answer 11

Removes low-energy x-ray photons which are of no use

Question 12

What is used to control the size of area irradiated by the primary beam?

Answer 12

Collimators

Question 13

Which 2 factors does photoelectric absorption depend on?

Answer 13

• Effective atomic number

- Number of atoms per unit volume (density of tissues)

Question 14

What is scatter and what does it cause?

Answer 14

When photons continue in different directions with lower energy and are not absorbed.
Results in random film/image blackening in the surroundings

Question 15

Photoelectric absorption has predominant interaction with…?

Answer 15

• Low energy photons

- High atomic number tissues

Question 16

Scatter has predominant interaction with…?

Answer 16

• Medium-high energy photons

- Low atomic number tissues

Question 17

What does kV control? What happens when you increase it?

Answer 17

• The energy of x-ray photons in the primary beam

- More photons have sufficient energy to penetrate the patient

Question 18

What do mAs control?

Answer 18

The number of x-ray photons produced

Question 19

What is exposure a combination of?

Answer 19

mAs and kVs - they are exposure factors

Question 20

To double exposure how much do mAs and kVs need to be increased by?

Answer 20

Increase mAs by 100%

Increase kVs by 15%

Question 21

On a radiograpah an area with complete exposure will appear…?

Answer 21

Black

Question 22

What are the 5 basic radiographic opacities from black to white?

Answer 22

Air
Fat
Soft tissue/fluid
Mineral (bone)
Metallic

Question 23

Is a light film over or under exposed?

Answer 23

Under

Question 24

What is meant by dynamic range in radiography?

Answer 24

Range of x-ray exposures over which a useful image can be obtained

Question 25

Describe the relationship between exposure, signal and dynamic range in:

1. conventional film
2. digital systems

Answer 25

1. narrow dynamic range, non-linear relationship between exposure and signal (s-shape on graph)
2. wide dynamic range, linear relationship between signal and exposure (straight line)

Question 26

What is the main health concern when it comes to radiography?

Answer 26

Ionising radiation

Question 27

Which other scanning method uses ionising radiation?

Answer 27

CT scanning

Question 28

What causes ionising radiation?

Answer 28

Scatter - travels in all directions

Question 29

What are some deterministic effects of ionising radiation?

Answer 29

Tissue reactions related to cell death e.g. skin burns, cataracts, bone marrow suppression, sterility

Question 30

What are the stochastic effects of ionising radiation?

Answer 30

Cell mutation related to DNA damage e.g. cancer inductions, birth defects

Question 31

What unit is the effective radiation dose given in?

Answer 31

sievert (Sv)

Question 32

Why is radiation weighting used?

Answer 32

Not all radiation is given in equal doses

It accounts for the biological effect of radiation type on tissue type

Question 33

What is the calculation for the absorbed radiation dose?

Answer 33

Energy imparted into the tissue/Mass of the tissue

Question 34

Who governs all work with ionising radiation?

Answer 34

Ionising radiations regulations 1999

Question 35

Safe working with radiation requires cooperation of which 3 groups of people?

Answer 35

• Health and safety executive
• Radiation Protection advisor
• Employer

Question 36

What are the 3 basic principles of radiation protection?

Answer 36

1. Ionising radiation should only be used where there is a clear justification for the procedure
2. Any exposure to personnel should be kept as low as reasonably practicable
3. No dose limit to personnel should be exceeded

Question 37

Doses over what level must be investigated?

Answer 37

15mSv per year

Question 38

The radiography room must be large enough for..?

Answer 38

• All involved to be at least 2m away from the primary beam

- Behind a protective screen/barrier

Question 39

What are boundary shielding requirements for scattered radiation and the primary beam?

Answer 39

• 0.5mm lead for scattered

- 2mm of lead for primary beam