Radiology 3

Question 1

In domestic energy supply, what is the typical voltage?

Answer 1

220/240 volts

Question 2

The current in domestic energy supply travels in a wavelength form of…

Answer 2

50 Hertz

Question 3

Typical domestic energy supply current

Answer 3

13 amp current (however, circuits can be fused at 3, 5 or 13 amps).

Question 4

Where is the domestic electricity supply converted to the x-rays needed in dentistry?

Answer 4

The tube head

Question 5

What can you do on the control panel?

Answer 5

1. the time of the exposure
2. the area of the exposure
3. the type of film we are taking (e.g bitewing etc)

Question 6

A

Answer 6

Cathode connection

Question 7

B

Answer 7

Filament

Question 8

C

Answer 8

Electron beam

Question 9

D

Answer 9

Tungsten target

Question 10

E

Answer 10

Glass housing

Question 11

F

Answer 11

Anode connection

Question 12

G

Answer 12

Bremsstrahlung ((German: “braking radiation”), and characteristic X-rays

Question 13

H

Answer 13

X-rays

Question 14

I

Answer 14

Filament focusing cup

Question 15

The filament - cathode

Answer 15

• Fine wire (tungsten)
• Current gets passed along it (8-10mA), electrons are excited, wire gets hot (may give off light).
• Electrons are lost from outer shell/orbits round the nucleus. Electron cloud forms around the cathode (focusing cup helps bring this together).

Question 16

The anode

Answer 16

• Small tungsten target embedded in copper
• Potential difference between anode and cathode (e.g. 70kV)
• Step up transformer gives rise to the change in voltage
• Due to the large potential difference, negatively charged electrons from the cathode are pulled over to the anode (attracted to the positive charge of the anode nuclei).
• Then they come to a sudden stop/decelerate and get rid of most of the energy that they contain.
• 99% of this energy is transferred into heat, 1% in x-rays.

Question 17

Function of the step up transformer in the tube

Answer 17

The step up transformer (coils of copper) facilitates the necessary increase in voltage:
Domestic mains supply = 240V
———–>
X-ray production voltage required = 70,000V

Question 18

Two types of x-ray spectra

Answer 18

1. Continuous spectrum
2. Characteristic spectrum

Question 19

Continuous spectrum

Answer 19

Bremsstrahlung / breaking radiation: electromagnetic radiation produced by a sudden slowing down or deflection of electrons. They display a wide range of photon energies. Moving round the nucleus loses energy - gradually, some of the electrons with less energy will move off to react with other atoms (much of the energy given off is as heat, however some of it is Bremsstrahlung radiation).

Question 20

Characteristic spectrum

Answer 20

Depends on material used in anode. Emitted by loss of electrons from K & L shells.

Question 21

Why is filtering out necessary?

Answer 21

• Small deflections are the most common, producing many low energy photons.
• These have little penetrating power and will not contribute to the useful x-ray beam.
• Filtration is necessary to remove radiation that would otherwise be absorbed by the body.

Question 22

What gives rise to high energy photons and how common are they?

Answer 22

Large deflections (which are less likely meaning there are few high energy photons).

Question 23

Maximum photon energy is directly related to…

Answer 23

kV across the X-ray tube

Question 24

What must happen for characteristic radiation to occur…

Answer 24

An incident electron has a direct hit with an electron in the K shell, it knocks the K shell electron out, and this is called the ejected orbital electron (the initial electron may also be ejected after interaction ‘bounces off’ - potentially with less energy than when it came in).

Question 25

What occurs once an incident electron has knocked an electron from the K-shell?

Answer 25

• The shell is no longer stable with electrons, therefore an electron from an outer shell drops down into the K-shell (going on until the outer shell and all inside shells are stable).
• However, that electron has too much binding energy, gets rid of the excess energy as an x-ray photon.

Question 26

Characteristic spectrum: which shell’s line spectra is of diagnostic importance?

Answer 26

K shell (58-69.5kV)

as those belonging to L shell are less than 10kV which would be absorbed within the X-ray tube

Question 27

X-ray tube needs to be operating at above____ for characteristic spectrum to be produced.

Answer 27

69.5kV

Question 28

If you were using a X-ray tube that works between 60-65kV we would only have ____________ radiation

Answer 28

bremsstrahlung

Question 29

Non-ionising radiation

Answer 29

Question 30

Ionising radiation

Answer 30

Question 31

Scattering

Answer 31

random change in direction after hitting something

Question 32

Absorption

Answer 32

deposition of energy in tissues

Question 33

Intensity

Answer 33

number of x-ray photons in a defined area of the beam

Question 34

Attenuation

Answer 34

reduction in intensity of beam due to scattering & absorption

Question 35

Ionisation

Answer 35

removal of electron from neutral atom to give -ve (electron) & +ve (atom) ions

Question 36

Penetration

Answer 36

the ability of photons to pass through or into tissues/materials

Question 37

What are the 4 main outcomes for an x-ray when it interacts with something?

Answer 37

1. Completely scattered with no loss of energy
2. Absorbed with total loss of energy
3. Scattered with some absorption & loss of energy
4. Transmitted unchanged

Question 38

Internal scatter

Answer 38

Radiation passes downwards into the patient’s body.

Question 39

Properties of x-rays

Answer 39

• Not detectable by human senses
• Produce a latent image on film emulsion
• Cause ionisation
• Can cause biological damage
• Cause certain salts to fluoresce & emit light

Question 40

Radiation dose

Answer 40

The radiation dose is the amount of radiation absorbed by the patient. Low energy photons often are absorbed by soft tissues