Radiology introduction

Question 1

What are x-rays

Answer 1

high energy electromagnetic radiation with a short wavelength = ionising radiation

they consist of photons and travel in straight lines

Question 2

What does ionising radiation mean

Answer 2

there is enough energy to detach electrons from atoms/molecules

Question 3

Outline what happens in an x-ray tube

Answer 3

1. At the cathode a tungsten filament is heated to emit electrons
2. These move to the anode to give tube current
3. Higher voltage accelerates the speed of electrons
4. Electrons are converted to photons (x-rays)

Question 4

What is the anode made of

Answer 4

A tungsten target in a copper block surrounded by oil to remove heat

Question 5

Why is the x-ray tube under vaccuum

Answer 5

So that there is no obstruction by air molecules

Question 6

What are the 3 x-ray producing collision

Answer 6

1. Continuous spectrum = rapid deceleration at target and energy is lost as x-rays
2. Characteristic spectrum = energy is specific to each atom
3. Combined spectrum = continuous and characteristic

Question 7

Define attenuation in regards to x-rays

Answer 7

This is where there is lower intensity of the main x-ray beam because there is absorption and scattering

Question 8

What are the 4 fates of x-rays

Answer 8

1. Unmodified Rayleigh scattering
2. Photoelectric effect = pure absorption
3. Compton effect = scattering and absorption
4. Pair production = pure absorption

Question 9

How are heat producing collisions made

Answer 9

When the incoming electron changes direction by the outer-shell tungsten electron there is energy loss as heat

Excitation and ionisation also results in heat loss

Question 10

When is a bitewing used

Answer 10

Caries detection

Question 11

When is a periapical used

Answer 11

• hepathology of tooth apex

- crown and root check ups

Question 12

When is a dental panoramic used

Answer 12

to look at TMJ and all dentition

Question 13

When is an occlusal used

Answer 13

to check for root trauma and unerupted teeth

Question 14

When is a CT used

Answer 14

to get a 3D image

Question 15

Define radiation absorbed dose

Answer 15

Energy absorbed per unit mass of tissue

Question 16

Define equivalent dose

Answer 16

Quantity calculated for individual organs

radiation absorbed dose X radiation weighing factor

Question 17

Define radiation weighing factor

Answer 17

biological effect of radiation shown; when higher there is a greater chance of tissue damage

Question 18

Define effective dose

Answer 18

whole body dose

Question 19

Define collective dose

Answer 19

effective dose X population

Question 20

What are the four types of biological effects with x-rays

Answer 20

1. Somatic deterministic (acute) = large dose, small time and immediate problems
2. Somatic deterministic (chronic) = long time after exposure; deathly
3. Somatic stochastic = by chance and so it has random occurence and there is no threshold
4. Genetic stochastic = mutation based

(stochastic effects are prevalent in dentistry)

Question 21

What is the safe dose

Answer 21

Dose below which stochastic effects do not occur

Question 22

What direct damage can x-rays cause

Answer 22

Damage to DNA/RNA molecular structure and so information cannot be passed on leading to cell death

In somatic cells this causes radiation induced malignancy

In reproductive cells radiation induced congenital abnormality

Question 23

What indirect damage can x-rays cause

Answer 23

Ionisation of water molecules producing free radicals which can damage DNA which then leads to cell death

Question 24

What 3 steps should be considered before taking radiographs

Answer 24

1. Justification; benefits > risk
2. Optimisation; exposure should be kept low
3. Limitation; shouldn’t exceed ICRP guidelines

Question 25

What are the dose reduction techniques

Answer 25

• regular equipment checks
• parameters of 60-90KV and 7-12mA
• aluminium filter
• collimation
• spacers
• having a controlled area where there is distance and shielding from x-ray tube and patients

Question 26

What is the purpose of an alaminium filter

Answer 26

Removes soft x-rays which are damaging because they are absorbed by tissue

Question 27

What is the purpose of collimation

Answer 27

Reduces the x-ray beam size which lowers scattering of radiation; rectangular > circular

Question 28

What is a spacer

Answer 28

It ensures the safe focus to skin distance is maintained and so lowers the dose

Question 29

What is the penumbra effect

Answer 29

A smaller focal point leads to a clearer image