Radiology

Question 1

How many bananas is equivalent to 1 x-ray. and how long a flight

Answer 1

50 bananas, 4 hour flight

Question 2

How x-ray can cause cancer

Answer 2

x-rays can cause ionsiation - Due to their high energy they can remove an electron from an atom it collides with and create a free radical. Free radicals steal energy from other molecules. If DNA is damaged it can mutate and cause cancerous cells

Question 3

Distance of focal spot to skin surface of patient. Distance between operator and X-ray tube (controlled area)

Answer 3

20cm
1.5m

Question 4

What causes light and dark x-ray film

Answer 4

Dark= over exposure
Light= under exposure

Question 5

The 3 planes that need to be checked for a DPT

Answer 5

Mid sagittal
Alar tragal
Focal trough (between 2 and 3. or side of nostril)

Question 6

Where is the pip located for a PA and a bitewing

Answer 6

-PA: Pip down to crown
-Bitewing: pip upwards to palate

Question 7

Exposure time for bitewings. And the kV and mA settings

Answer 7

-anterior= 0.2s
-posterior=0.25s
66kV, 8mA

Question 8

In the X-ray tube, what % is heat and what is x-ray

Answer 8

1% x-rays
99% heat

Question 9

What are the 5 principles of shadow casting (what is required for a good quality image. Do you want distance between object, source, film to be small)

Answer 9

1. Radiation source as small as possible
2. Source to object distance large
3. Object to film small
4. Object and film parallel
5. x-ray beam perpendicular to object and film

Question 10

Definition of resolution and sharpness

Answer 10

how well the details/ boundaries/ edges are reproduced

Question 11

What 5 things can cause unsharp images

Answer 11

1. Movement of patient
2. Distance of object to source
3. Distance of object to film
4. High F speed (required to reduce radiation) causes unsharpness
5. Pixel size

Question 12

For a sharp image, do you want a large/ small distance between i) source to object. ii) object to film

Answer 12

I) large. Penumbra is smaller. Less magnification as beam less divergent
ii) small

Question 13

What is i) cervical burnout ii) overlapping. the causes

Answer 13

I) radiolucent band around necks of teeth due to lower penetration of the beam
ii) no inter proximal areas due to poor horizontal angulation.

Question 14

what does the kilovotlage refer to. What does a lower value mean. What value is usually used, and what is used for soft tissues

Answer 14

-70 used, 60 used for soft tissues
-it is the difference in potential applied to the X-ray tube. Adjusts the penetration and exposure and contrast
-beam quality
-lower= increased contrast
-higher= gets through patient quicker to reduce exposure time. darker film

Question 15

what does the current refer to

Answer 15

beam quantity
intensity fo photons exiting the tube

Question 16

The steps in x-ray production in the tube. the different components

Answer 16

X-ray tube is a vacuum that converts electronic power into x-rays
-a transformer increases the voltage from the mains, to 40-90kV
-oil is used for cooling
-at the cathode, the wire is super heated so electrons form a cloud
-electrons accelerated by potential difference and attracted to positive anode
-electrons hit at higher energy and release x-rays as they slow down
-hotter means more electrons, more x-rays, higher intensity

Question 17

What happens to the radiation dose every time you double your distance away from the source

Answer 17

radiation quarters

Question 18

what is scatter and how it affects the film

Answer 18

sometimes only a portion of a photons energy is transferred to the matter and can deflect off the matter. Can contaminate the film with fog. Can be minimised using collimators and aiming devices

Question 19

What is the photoelectric effect

Answer 19

-the effect increases with atomic number
-incoming photon hits electron in an atom and transfers its energy to it
-electron knocked out
-atom becomes unstable
-valancy filled by electron from higher shell
-energy released in the form of light

Question 20

What is the Compton scattering effect

Answer 20

-increases with increased kV
-incoming photon hits electron in atom
-photon and Electron both deflect in different directions
-this adds to the patients dose. Photons will scatter many times, losing energy each time

Question 21

What chemical is on the film and how it works

Answer 21

x-ray hits silver bromide crystals on film. Become sensitised and unstable. Electrons attracted. Silver ions reduced to become black metallic silver atoms.
-highly dense amalgam, means x-rays poorly penetrate as they are absorbed so do not hit film and it appears white
-less dense soft tissue means more penetration and appears blacker

Question 22

How Many micro SV is a full DPT

Answer 22

19