B - Intro to Physics

Question 1

Was X-Ray discovered or developed?

Answer 1

Discovered

Question 2

Who was X-Ray discovered by?

Answer 2

Wilhelm Roentgen in 1895

Question 3

In what year did medical imaging commence?

Answer 3

1896

Question 4

In what year Edison create the fluoroscope?

Answer 4

1898

Question 5

What is non-ionizing radiation?

Answer 5

Low frequency EMR waves
Photon energy too low to ionize atoms
Causes heating effect

Question 6

What is ionizing radiation?

Answer 6

High frequency EMR waves
Photon energy high enough to ionize atoms
Causes chemical reaction and damages living cells

Question 7

What are the properties of X-Rays?

Answer 7

No mass
Electrically neutral
Invisible
Travel at speed light
Highly penetrating
Travel in straight lines in a divergent beam
Diagnostic range of energy 15-150 keV
Cause certain substances to fluoresce
Can expose photographic film
Produce secondary radiation
Can ionize matter
Can induce biological changes due to ionization

Question 8

What is the function of an X-Ray tube?

Answer 8

Converts energy to form radiation

Question 9

How does an X-ray tube convert energy to form radiation?

Answer 9

The electrical energy is received and it is then converted into heat or x-radiation

Question 10

What is kVp (kilovoltage peak) ?

Answer 10

kVp - the maximum voltage applied across an X-ray tube. It determines the kinetic energy of the electrons accelerated in the X-ray tube and the peak energy of the X-ray emission spectrum. The actual voltage across the tube may fluctuate

Question 11

What is mAs (milliamps x second) ?

Answer 11

Controls the tube current and how many electrons produced at the cathode. Determines image density.

mAs controls how many electrons are produced at the cathode. The more electrons produced at the cathode the more x-rays that will be produced at the anode. The more x-ray beams then more x-rays will hit at each part of the x-ray where it was already hitting. Since mAs has nothing to do with the energy of the beam it won’t penetrate any different parts of the body, just make the parts it already is darker.

Question 12

What is keV (kiloelectron volt) ?

Answer 12

Unit of energy of the x-ray photon. Determines whether hard or soft x-rays.

X-rays with high photon energies (above 5–10 keV, below 0.2–0.1nm wavelength) are called hard X-rays, while those with lower energy are called soft X-rays

Question 13

What is a cathode?

Answer 13

This provides the source of electrons

Question 14

What is an anode?

Answer 14

Acts as a target for the electrons and releases radiation in the form of photons

Question 15

What is information you know about a cathode?

Answer 15

Controlled source of electrons
Negatively charged
Electrons produced by heating a filament coil, usually made of Tungsten
Filament coil sits within a Focussing Cup, usually made from Nickel
Focussing cup provides electrostatic focussing of the beam towards the anode
Electrons are released from the filament using energy = HEAT
The filament is heated using the electrical current that passes through it
This process is called THERMIONIC EMISSION

Question 16

What is information you know about an anode?

Answer 16

Anode is a metallic bevelled disc where the x-ray beam is produced
Positively charged
Converts the energy of the electrons into photons (x-rays)
Heat is a by-product of this and is dissipated through the spinning of the anode
Disc is usually made of Tungsten – High atomic no. and melting point, provides more efficient Bremsstrahlung production than low atomic no’s.
Body of anode is often Molybdenum and Graphite – Good for heat storage
Anode is attached to a large copper rotor which allows it to spin up too 10,000 RPM with a temperature of up to 2000 degrees C

Question 17

What is the focal spot?

Answer 17

This is the point at which
the x-ray beam is produced
Can have fine or broad focal spot size

Question 18

What are the common sizes of a focal spot?

Answer 18

1.0mm
1.2mm

Question 19

When is a small focal spot used?

Answer 19

used when spatial resolution is important, used to create sharp images, but also withstand heat loading without melting

Question 20

When is a larger focal spot used?

Answer 20

when short exposure time is a priority

Question 21

Size and shape of electron beam is determined by?

Answer 21

Dimensions of tungsten filament
Construction of focussing cup
Position of filament in focussing cup
Electric field between cathode and anode (focal spot increases as current increases due to repulsion of adjacent electrons, also known as blooming effect)
Size of focal spot affected by angle of anode

Question 22

What are additional components of an x-ray?

Answer 22

Tube Envelope
Tube Housing – Functions as a shield, absorbs stray x-rays, large surface area to dissipate heat, oil between housing and envelope = electrical insulation
Dielectric Oil – Helps to dissipate heat from the anode target
Rotor – Helps to spin the anode target
Induction Stator – This, along with rotor, make up induction motor which spins anode target
Tube Window – Usually made form beryllium not glass, allows x-ray beam to exit the tube without interruption

Question 23

What is the tube envelope?

Answer 23

X-tube components are all contained in tube housing
Provides support and electrical insulation
This provides a vacuum to keep electrons from straying, support to components and electrical insulation
Usually made of glass, but can also be metal or ceramic
A ‘window’ exists in the housing to allow beam to exit, this is usually beryllium not glass

Question 24

What are the 2 types of photons/radiation?

Answer 24

Bremsstrahlung
Characteristic

Question 25

What is the x-ray beam made up of?

Answer 25

photons of varying energies

Question 26

What is Bremsstrahlung radiation?

Answer 26

High energy electrons bombard anode target and penetrate close to nucleus of atoms of that anode material
The electrons get close to the nucleus of the atom due to its positive charge and are subsequently influenced by its electrical field
This influence changes the course of the travelling electron, and causes it to slow down and alter direction. This is the electron losing some of its KINETIC ENERGY
Lost energy is emitted as an x-ray photon, or Bremsstrahlung radiation
“Braking” Radiation in German

Question 27

What is characteristic radiation?

Answer 27

During this interaction, the incident electron collides with a K shell electron in an anode target atom
The K shell electron is ‘ejected’ (only if the incident electron has equal to or greater than the binding energy of the K shell electron). This leave a ‘hole’
An outer shell (L, M) electron drops down into this ‘hole’, releasing some of its energy as it does so
This energy released is in the form of an x-ray photon, and is characteristic to the atomic number of the atom from which it has been released
The energy of the photon will be equivalent to the energy difference between the outer and inner shell electrons
For example: Photons from a Tungsten target will have an energy ranging from 57.98keV and 59.32keV

Question 28

Once we have our x-ray beam, what happens when it reaches our patient?

Answer 28

Various types of interaction can occur between an x-ray photon and ‘matter’ (this could be any object but we will refer to this as our patients)

There are three possibilities:
There may be no interaction
Absorption
Scatter