Principles of radiography

Question 1

2 types radiographic image

Answer 1

Bones dark (positive image) or bones white (negative image)

Question 2

Key requirements for x-ray production

Answer 2

electron source, method for accelerating electrongs, a heavy metal target (tungsten)

Question 3

How are x-rays produced?

Answer 3

when fast electrons collide with atoms of a heavy metal such as tungsten.

Question 4

X-ray absorption depends on ? 3 Effect of increasing any of these?

Answer 4

tissue density, atomic number of tissue elements, tissue thickness (increasing any of these increases the number of electrons in the x-ray path).

Question 5

What is Bremsstrahlung radiation?

Answer 5

Fast electrons are slowed as they approach a tungsten nucleus –> loss of energy = x-rays. Bremsstrahlung results in a broad continuous range of x-ray energies.

Question 6

Is air or metal more radiolucent on an x-ray?

Answer 6

Radiolucent (=black), air is more radiolucent than metal (opaque/white on an x-ray)

Question 7

How do you distinguish parenchymal organs, muscle and fluids on an x-ray?

Answer 7

You can’t unless you add a contrast media

Question 8

What is opacity?

Answer 8

A white or light grey area on a radiograph corresponds to a body part that absorbs x-rays (i.e. is opaque to x-rays)

Question 9

What is lucency?

Answer 9

A black or dark grey area on a radiograph represents a part of the body that allows more x-rays to pass through (i.e. is lucent to x-rays)

Question 10

Equation for mAs

Answer 10

= milliamps (mA) * time (seconds)

Question 11

Define milliamperes (mA)

Answer 11

The current (number of electrons) passing across the x-ray tube. (time in the equation for mAs isthe duration of this current)

Question 12

How do you increase the number of electrons passing through the x-ray tube/increase the number of x-rays produced/make the radiograph darker?

Answer 12

Increasing the current and/or increasing the time

Question 13

Typical range for radiographing small animals

Answer 13

25-300mA and 0.01-0.3s

Question 14

When to increase the mA setting? 2

Answer 14

High mA settings are used to minimise the exposure time and avoid motion blurr.

Question 15

Define kVp

Answer 15

Kilovoltage peak - the voltage applied across the x-ray tube

Question 16

Effect of increasing the kVp - 2

Answer 16

Increased the number of x-rays produced AND increases the x-ray beam energy which increasing the penetrating power of the x-ray beam (the higher the voltage, the faster the electrons travel)

Question 17

Use - low kVp exposure

Answer 17

Very small body parts (e.g. extremities)

Question 18

Use - high kVp exposure

Answer 18

Thicker body parts (e.g. thorax)

Question 19

Types of positive contrast media - 2

Answer 19

• Iodide ions - high atomic number therefore absorbs x-rays and appear white (IV or bladder imaging)
• Barium (sulphate) - to look at GIT disease.

Question 20

In an x-ray tube, what is the function of the copper that the tungsten is mounted on?

Answer 20

When the copper heats up (conducts heat from electrons), prevents the tungsten heating up too much and splitting

Question 21

Why is the tungsten, copper and aluminium cup put in a high vaccuum?

Answer 21

To stop air disrupting the path of electrons

Question 22

Describe the electromagnetic spectrum

Answer 22

Low energy = AC power, radio, television, infrared, radar, visible, ultraviolet, gamma rays, x-rays

Question 23

Define KeV

Answer 23

kiloelectron volts (90= peak energy/highest)

Question 24

Why don’t low x-rays escape?

Answer 24

They are filtered/absorbed by 2mm aluminium.

Question 25

How does changing the kVp affect the shape of the x-ray spectrum?

Answer 25

It changes the shape of the x-ray spectrum - peak and median energies change.

Question 26

Are there standard kVp size guidelines

Answer 26

kVp numbers vary between x-ray machines. Increase the kVp the thicker the animal’s body part.