How are X-rays produced?

Question 1

Who discovered x-rays?

Answer 1

Discovered in 1895 by Wilhelm Rontgen,

Question 2

how did wilhelm discover x-rays?

Answer 2

he discovered it accidently when he was experimenting with crooks tube, which is a glass tube without any air and current is passed through it. Coloured light (visible light) is emitted from the tube.

He then covered the tube with a black box and at the end of his lab a fluoresced plate which fluoresced when the crooks tube turned on. Some other rays were also produced which is now known as x-rays.

Question 3

when was the first radiograph taken?

Answer 3

1895

Question 4

when was the first dental radiograph taken?

Answer 4

1st dental radiograph in 1896 by Otto Walkhoff.

Question 5

what is the main part of the x-ray device?

Answer 5

The whole of the main part of the X-ray unit is correctly referred to as the tube head. This is what you hold and move to different positions when carrying dental radiographic examinations.

Question 6

what does the tube head consist of?

Answer 6

filament (cathode)
glass x-ray tube
tungsten target (annode)
oil
step up transformer
spacer cone

Question 7

what does the glass x-ray tube consist of?

Answer 7

Inside the glass x-ray tube is anode- positively charged and is tungsten target surrounded by copper good conductor

Cathode - negatively charged tungsten wire filament

Current is supplied to the anode and difference in voltage (in the range of 60-70kv) is setup between the anode and cathode.

Question 8

what is the purpose of the x-ray glass tube?

Answer 8

It is where the x-rays are produced.

Question 9

what is the purpose of the step-up transformer?

Answer 9

The step-up transformer is required to step up or increase the mains voltage of 240 volts to the very high voltage that is required across the x-ray tube to (60-70 kv).

Question 10

why is the x-ray tube surrounded by oil?

Answer 10

The X-ray tube is surrounded by oil to facilitate the removal of the considerable amount of heat that is created during the production of X-rays.

Question 11

whats the purpose of the spacer cone?

Answer 11

The spacer cone is the device for indicating the direction of the beam and setting the ideal distance of the target to the skin.

Question 12

What is an atom?

Answer 12

An atom is the smallest part of an element that can exist and yet still retain its chemical identity.

Question 13

what is the nucleus composed of?

Answer 13

• Protons – carry a positive charge
• Neutrons – uncharged
  Atomic Number, is the number of protons in the nucleus.

Question 14

how are x-rays produced?

Answer 14

X-rays are produced at the atomic level within the glass x-ray tube

1. An electric current flows through the filament the negatively charged cathode, and heat causes a cloud of electrons (boiled) to collate around the filament.
2. The voltage provided by the step-up transformer accelerates electrons towards the Tungsten target of the anode. The kinetic energy of electrons is converted into heat once it hits the target of the anode (99% conducted by copper to the oil).
3. 1% of that kinetic energy is transferred into x-rays. X rays are produced on the atomic level.

Question 15

what does the beam of electron interact with at the target?

Answer 15

X rays are produced on an anatomic level due the electrons undergoing interaction with both the orbital electrons and the nucleus of the target atoms.

Question 16

How does the beam of electrons interact with the nucleus?

Answer 16

When an electron passes close to a nucleus the strong attractive force (opposite charges attract) causes it to be decelerated rapidly and deflected violently from its original path.
As a result, the electron suffers a sudden loss of kinetic energy (ie it slows down) and emits an x-ray photon.

Question 17

During the interaction of the electron and nucleus what effects the energy of the x-rays that are produced?

Answer 17

The energy of the emitted x-ray depends on the strength of the electron-nucleus interaction and is equal to the kinetic energy lost by the electron, which can be any amount from virtually zero right up to its entire kinetic energy (ie the electron is brought to a complete stop).

If the incoming electron loses a lot of kinetic energy then a higher energy x-ray is produced.

Question 18

what are “bremsstrahlung” x-rays ?

Answer 18

when X-rays are emitted with a continuous range of energies.

Question 19

what does the kinetic energy of the electron form beam depend on?

Answer 19

The tube voltage (or kV).

Increasing the kV increases the number of high energy photons and the maximum energy of a photon has also increased.

Question 20

How does the beam of electrons interact with the electrons of the tungsten atom?

Answer 20

Incoming electrons collides with an electron of the tungsten atom and causes that electron to be ejected from the atom. The incoming electron get deflected creating a gap in the electron shells. An electron will drop down from the outer shell into the inner shell to replace the one that has been lost.

As this happens an x-ray is produced and the energy of this x-ray produced will match the difference in energies between the two electron shells, so the x-ray produced will have a characteristic energy.

Question 21

What is characteristic x-rays?

Answer 21

Second way an electron can be produced, as some of the beam of electrons interacting with the electrons in the shells of the tungsten atom.

Question 22

What is the significance of the energy of photons?

Answer 22

Low energy photons are dangerous they are absorbed into patient tissue. They are unable to penetrate the patient and contribute to an image.

High energy photons are useful diagnostically they pass through the patient and hit the photographic film.

Question 23

What is the purpose of the aluminium filter?

Answer 23

The beam is made-up of many low energy photons. An aluminium filter used to remove these energy photons from the beam before it hits the patient.

Question 24

What is precaution when taking an x-ray?

Answer 24

When the button is pressed to take the x-ray, there are audible and visible sign so that it is known that an x-ray is happening.

Question 25

What are the exposure factors?

Answer 25

• Kilovoltage (kVp) is the set
• Time – can be controlled, can control the number of x-rays that pass through the patient
• Milliampere seconds (mA) – current and is fixed

Question 26

What happens when you change the kV?

Answer 26

If you increase the kV you increase the quality of the photons that are produced. Higher energy photons means lower dose. However, high kV kV creates a less contrasting image.

Lowering the kV increases the images contrast. This is because the x-rays will have less energy and these x-rays are more likely to be stopped by the patient. However there is a higher dose.

Question 27

What happens when you change the milliampere-seconds (mAs)?

Answer 27

• Too high mA/exposure to time will lead to an overexposed dark image
• Too low mA/exposure to time will lead to an underexposed light image

So need to have a balance. mAs is directionally proportional to the dose.

Question 28

What is the focus to skin distance?

Answer 28

Focal spot on the target to the end of the spacer cone that touches the patient face.

If we increase the focus to skin distance, we reduce the dose to the patient.

Question 29

What is collimation?

Answer 29

This is where we apply a rectangular collimator to the very end of the spacer cone, this narrows the shape of the beam to a rectangle. This is used as the detector we used is rectangular shaped.

Only exposes the area on the patients that will be received by the detector, reducing the dose.