XR production 1

Question 1

What are some elements of an XR tube?

Answer 1

-Anode
-cathode
-electrons
-vacuum
-target
-source of electrons

Question 2

why is a vacuum needed?

Answer 2

So there’s nothing else the electrons will interact with between the cathode and the anode.

Question 3

Why are electrons attracted to the anode?

Answer 3

Electrons are negatively charged, and a positively charged anode which creates a force of attraction called a coulomb force.

Question 4

what happens when electrons interact with the anode material?

Answer 4

Convert potential energy to kinetic energy, but when they interact, they give up that energy in the
form of radiation (x-ray photons).

Question 5

what is the definition of an electron volt?

Answer 5

defined as the amount of energy gathered by a single electron when moved across a potential difference of one volt.

Question 6

what are these radiographic factors?
-kV/kVp?
-mA
-ms
-mAs

Answer 6

kV- potential difference between anode and cathode
mA- current flowing between anode and cathode
ms- time during which current flows in the tube
-mAs- product of the tube current in milliamps and the time in seconds (how many electrons are flowing during our exposure).

Question 7

x rays are produced by which 2 processes?

Answer 7

-General radiation (bremsstrahlung)- e- interacting with the nucleus of target atoms.
-Characteristic Radiation e- interacting with electrons in the shells of target material.

Question 8

Outline bremsstrahlung

Answer 8

-tungsten atom in anode has many electrons.
-accelerated electrons are attracted to the nucleus because of coulomb force.
-As the electron gets closer to the nucleus its diverted from its path and gives up some of its kinetic energy.
-This produces either heat or photon energy.
-the closer it gets to the nucleus the more energy is released because there is a higher breaking force.

Question 9

What does bremsstrahlung produce?

Answer 9

-Wide range of photon energy
-mostly heat
-Energy depends on proximity of electron to the nucleus and charge associated with the nucleus.

Question 10

What is filtration?

Answer 10

matter that gets in the way of the x ray photons as its trying to get out of the x ray tube, e.g. glass.

Question 11

What does the minimum and maximum energy depend on regarding bremsstrahlung?

Answer 11

Minimum- filtration of XR beam
Maximum- Applied voltage

Question 12

What is photon energy?

Answer 12

Measure of the ability of the XR photon to penetrate matter.
-higher the energy of XR photon, more likely it is to penetrate matter compared to a lower energy photon.

Question 13

Outline the concept of XR beam intensity and quantum noise.

Answer 13

-XR beams distributed randomly, XR beam intensity won’t be the same across the whole image field.
-there will be some variation, this called quantum noise.
-If the noise is too big it can obscure things in the image.
-Reduce the noise by increasing no. of XR photons per mm²

Question 14

In simple terms, what is characteristic radiation?

Answer 14

outer-shell electrons fill a vacancy in the inner shell of an atom, releasing X-rays in a pattern that is “characteristic” to each element.

Question 15

Explain the process of characteristic radiation

Answer 15

• Accelerated electrons interact with the k shell electrons.
• If the electron has sufficient kinetic energy to overcome the binding energy of this k shell electron, it can eject it out of its orbit.
• That will leave a vacancy which is then filled from the higher shells above it.
• Electron drops down from L shell to K shell, in doing so it gives off characteristic radiation.
  The energy given off is equal to the difference in the binding energies between the two shells.

Question 16

what happens to any excess energy during characteristic radiation?

Answer 16

it is shared between the electrons

Question 17

what is the XR beam spectrum?

Answer 17

At a high level the x-ray spectrum is a plot of the Number of X-ray Photons (y-axis) as a function of the energy level in keV (x-axis).

Question 18

What does the XR beam spectrum show us?

Answer 18

Needs enough energy to overcome the binding energy.
Max kinetic energy depends on the voltage
If voltage isn’t high enough, we don’t see characteristic x ray peaks.

Question 19

XR beam quality

Answer 19

-indicates ability of XR beam to penetrate an object or indicate the energy of the beam.
-beam quality is referred to as being hard or soft, meaning it is more of less penetrative.

Question 20

XR beam spectrum: Effect of altering exposure factors. What 3 factors can you alter?

Answer 20

-Tube potential (kV)
-XR tube current (mA)
-Increasing filtration thickness

Question 21

XR beam spectrum: What are the effects of changing tube potential (kV)

Answer 21

increases:
-intensity- more X-rays per mm^2
-average energy
-maximum energy

-Peaks on the spectrum are characteristic of the anode material.
-if kV is high enough, characteristic XRs will be produced.

Question 22

XR beam spectrum: What are the effects of increasing XR tube current (mA)

Answer 22

increases: intensity

no change:
-average energy
-minimum energy
-maximum energy

Don’t get any difference in the distribution of energies. The average beam energy stays the same.

Question 23

XR beam spectrum: What are the effects of increasing filtration thickness

Answer 23

increases: average energy
decrease: intensity

lower energy photons are preferentially absorbed compared to higher energy.

More filtration leads to more photons being absorbed. So you get a spectrum that is reduced.
Low energy XR photons can be easily absorbed by the patient. So we need to get rid of these as these are dangerous and can produce skin burns. To do this we add some extra filtration, e.g. 2mm of aluminium.

Question 24

Air Kerma

Answer 24

-quantity used to express radiation the concentration delivered to a point, such as entrance surface of a patients body
-Measure of the amount of radiation energy in Joules (J), deposited in or absorbed in a unit mass (kg) of air
-Also referred to entrance surface dose and has units of Gray
-Not actual dose in an individual patient as this is impossible to calculate accurately.

Question 25

Divergent XR beam

Answer 25

-Photons diverge, covering a wider area,
Same no. of photons but wider area, means XR beam intensity has decreased.

Question 26

What is inverse square law

Answer 26

-When you double the distance, you quarter the XR beam intensity.
This is called inverse square law. As the intensity is inversely proportional to the square of the distance.

-As distance increases the XR be a intensity and exposure decreases.