General Science Review Physics: X-ray Production

1
General Science ReviewPhysics X-ray Production
Radiation InteractionsX-ray Exposure
FactorsRadiographic Density Contrast

• RAD TECH A
• Week 5

2
ATOM

• Smallest particle of matter that has the
  properties of an element.
• Contains a small, dense, positively charged
  center (nucleus).
• Nucleus surrounded by a negative cloud of
  electrons.
• Electrons revolve in fixed, well-defined orbits
  (energy levels).

3
ATOM
4
3 Fundamental Particles of an Atom

• Electron
• Proton
• Neutron

5

• Electrons can only exist in certain shells that
  represent electron binding energies
• K, L, M shells (K is closest to the nucleus)
• The closer an electron is to the nucleus, the
  higher the binding energy (strength of attachment
  to the nucleus).

6
Atoms

• In their normal state, atoms are electrically
  neutral
• If an atom has an extra electron or has had an
  electron removed, it has been ionized.

7
How X-rays are Created

• To produce x-rays, you need 3 things
• A source of electrons
• A force to move them rapidly
• Something to stop them rapidly
• All 3 conditions met in an x-ray tube

8
Early X-ray Tube
9
(No Transcript)
10
The X-Ray tube is the single most important
component of the radiographic system. It is the
part that produces the X-rays
11
Glass Envelope

• MADE OF PYREX GLASS TO WITHSTAND HIGH HEAT LOAD
• IS GAS EVAUCUATED
• (so electrons wont collide with the air
  molecules in the tube)

12
Heated filament emits electrons by thermionic
emission
Electrons are accelerated by a high voltage
Copper rod for heat dissipation
X-rays produced when high speed electrons hit the
metal target
13
How are X-rays Made?

• X-rays are produced when electrons strike a metal
  target.
• The electrons are ejected from the heated
  filament and accelerated by a high voltage
  towards the metal target.
• The X-rays are produced when the electrons
  collide with the atoms of the metal target.

14
Cathode (-)

• The cathode (negative electrode) contains a
  tungsten wire (filament) wound in a coil.
• Mounted in a holder called a focusing cup.
• Filament is heated acts as a source of
  electrons.
• The temperature of the filament controls the
  quantity of electrons emitted from it.
• Temp. is raised by increasing current (mA)
  milliamperage.

15
Thermionic Emission

• When the current (amps) in the filament is
  intense enough, the outer-shell electrons of the
  filament are boiled off and ejected from the
  filament.
• Tungsten filaments provide higher thermionic
  emission than other metals.
• Negative charge

16
Anode ()

• The anode (positive electrode) is usually a
  copper block with a plate of tungsten (target).
• Tungsten has a high melting point, can withstand
  extreme heat, is more efficient _at_ producing
  x-rays.
• Small area on target where electrons strike is
  called the focal spot this is the origin of the
  x-rays.

17
Rotating Anode

• Driven by an electromagnetic induction motor 2
  principle parts
• Stator outside the glass envelope, series of
  electromagnets
• Rotor inside the glass envelope, shaft made of
  copper iron.

18
X-ray Production

• Positive voltage is applied to ANODE
• Negative electrons attracted across the tube to
  the positive ANODE.
• Electrons slam into anode suddenly stopped.
• X-RAY PHOTONS ARE CREATED

19
X-ray Production

• When a high electrical potential (kilovolts) is
  applied across the cathode anode, the electrons
  will strike the target with tremendous energy.
• The higher the voltage, the greater the speed.

20
X-ray Production

• Electron beam is focused from the cathode to the
  anode target by the focusing cup
• Electrons interact with the electrons on the
  tungsten atoms of target material
• PHOTONS sent through the window PORT towards
  the patient

21
Heat Production

• Heat x-rays are produced by the impact of the
  electrons.
• Only about 1 of the energy resulting from the
  impact become x-rays.
• Most of the energy will become heat.

22
X-ray PhotonsWaves or Particles?

• electromagnetic waves of shorter wavelength and
  higher energy than normal light. But the debate
  over the nature of the rays are they waves or
  particles?
• Photons can be described both as waves and
  particles.

23
Electromagnetic Spectrum

• X-rays have wavelengths much shorter than visible
  light, but longer than high energy gamma rays.
• Because of short wavelength high freq., x-rays
  are able to penetrate materials that absorb or
  reflect light.

24
X-ray Properties

• Are highly penetrating, invisible rays which are
  a form of electromagnetic radiation.
• Are electrically neutral and therefore not
  affected by either electric or magnetic fields

25
X-ray Properties

• Can be produced over a wide variety of energies
  and wavelengths (polyenergetic heterogeneous).
• Release very small amounts of heat upon passing
  through matter.

26
X-ray Properties

• Travel in straight lines.
• Travel at the speed of light, 3 X 108 meters per
  second in a vacuum.
• Can ionize matter.

27
X-ray Properties

• Cause fluorescence of certain crystals.
• Cannot be focused by a lens.
• Affects photographic film.

28
X-ray Properties

• Produce chemical and biological changes in matter
  through ionization and excitation.
• Produce secondary and scatter radiation.

29
Interactions
30
Kinetic Energy (KE)

• The energy of motion
• Stationary objects have no KE
• Objects in motion have KE proportional to their
  mass to the square of their velocity
• Electrons traveling from cathode to anode are
  sometimes called projectile electrons.
• The electrons KE is converted into thermal
  energy (heat) electromagnetic energy (x-rays).

31
X-ray Exposure Factors

• TECHNIQUE SELECTION
• Radiographer selects the kiovoltage peak (kVp),
  milliamperage (mA) time (s).
• Milliamperage time mAs
• (milliamperage multiplied by a set time
  measured in seconds)

32
Kilovoltage Peak

• kVp
• One kilovolt 1000 volts
• The amount of voltage selected for the x-ray
  tube.
• Range 30 to 150 kVp
• kVp controls contrast

33
Milliamperage

• mA
• One milliampere one thousandth of an ampere.
• The amount of current supplied to the x-ray tube
• How many x-rays will be produced
• Range 10 to 1200 mA

34
Time

• In seconds
• How long x-rays will be produced
• 0.001 to 6 seconds

35
Milliampere Seconds

• Technologists think in terms of mAs
• Calculated by mA x seconds
• Ex 100mA X 0.2s 20 mAs
• How many x-rays will be produced and for how
  long.
• Modern x-ray machines only allow control of mAs

36
Imagine this

• If one changes the mA station from 200 to 400 mA,
  twice as many electrons will flow from the
  cathode to the anode.
• So mA controls how many electrons are coming at
  the target.
• mAs is a combination of how many and for how long
  (seconds)

37
200 mA
400 mA
38
Change in kVp

• kVp controls the energy level of the electrons
  and subsequently the energy of the x-ray photons.
• A change from 72 kVp will produce
• x-rays with a lower energy than at
• 82 kVp
• Difference between a ball traveling 72 mph and 82
  mph (how much energy did it take to throw the
  ball at the rates?)

39
Image Production

• Primary Radiation The beam of photons, B4 it
  interacts with the pts body.
• Remnant Radiation The resulting beam that is
  able to exit from the patient.
• Scatter Radiation Radiation that interacts with
  matter only continues in a different direction
  not useful for image production.
• Attenuation Primary radiation that is changed
  (partially absorbed) as it travels through the pt.

40
Path Attenuation of X-ray Beam
41
Tube Interactions

• Heat 99
• X-ray 1
• Bremsstrahlung
• (Brems) 80
• Characteristic20

42
Anode Heat

• Projectile e- interact with outer shell e- but do
  not have enough energy to remove them.
• Outer shell e- only becomes excited into a higher
  energy level then drop back down to normal
  energy
• Heat is generated

43
Characteristic Radiation

1. Projectile electron removes K shell electron
   (hole is produced)
2. Outer shell electron falls into hole in the K
   shell (ionization)
3. Emission of x-ray photon

44
Bremsstrahlung Radiation(Slowing down or Braking)

• Projectile e- completely passes by the orbital e-
• Comes very close to the nucleus
• As the proj. e- passes the nucleus, it slows down
  and changes direction
• Slowing down reduces KE x-ray is produced

45
Patient Interactions

1. Photoelectric Effect
2. Compton Scattering
3. Classic Coherent Scatter
4. Pair Production
5. Photodisintegration

46
Photoelectric Effect

• X-ray photon absorption interaction
• Occurs when an x-ray is totally absorbed during
  the ionization of an inner-shell electron
• X-ray photon disappears and the k-shell e- (now
  called a photoelectron) is ejected from the atom.

47
Photoelectric Effect
48
(No Transcript)
49
Compton Scatter

• X-ray photon interacts with an outer-shell e-
  ejects it from the atom
• The x-ray continues in a different direction
  with less energy

50
Compton Scatter
51
Compton Scatter

• Scattered x-rays provide NO useful information on
  the film
• Contribute to film fog inferior radiograph, not
  as clear an image
• Can create radiation exposure hazard (esp. during
  fluoroscopy) Personnel in the room can be
  exposed.

52
(No Transcript)
53
Classical Coherent Scatter

• Interaction between low energy x-rays the atom,
  causing the atom to become excited
• Direction of 2nd photon is changed, no loss in
  energy, no e- being ejected.

54
Classical Coherent Scatter
55
Classical Coherent Scatter
56
Pair Production

• Occurs when an x-ray photon interacts with the
  nuclear force field and two electrons are
  created
• 1. Positron (positively charged electron)
• 2. Negatively charged electron

57
(No Transcript)
58
Pair Production
59
Photodisintegration

• High energy x-ray photons that escape interaction
  with electrons nucleus.
• Instead, photon is absorbed by the nucleus, the
  nucleus becomes excited, and releases a nuclear
  fragment.

60
Photodisintegration
61
Review!!!
62
Photoelectric Effect - Patient
63
Classical Coherent Scatter - Patient
64
Compton Scatter - Patient
65
Pair Production - Patient
66
Photoelectric Effect - Patient
67
Characteristic Radiation - Tube
68
Bremsstrahlung Radiation - Tube
69
Why you see what you see

• The films or images have different levels of
  density different shades of gray
• X-rays show different features of the body in
  various shades of gray.
• The gray is darkest in those areas that do not
  absorb X-rays well and allow it to pass through
• The images are lighter in dense areas (like
  bones) that absorb more of the X-rays.

70
Images

• DENISITY THE AMOUNT OF BLACKENING DARKNESS ON
  THE RADIOGRAPH
• CONTRAST THE DIFFERENCES BETWEEN THE BLACKS TO
  THE WHITES

71
Density

• mAs
• mA AMOUNT of electrons sent across the tube
  combined with TIME (S) mAs
• mAs controls DENSITY on radiograph primary
  function of mAs is DENSITY

72
Contrast

• Kilovolts to anode side kVp
• Kilovolts controls how fast the electrons are
  sent across the tube
• kVp controls CONTRAST on images

73
Radiolucent vs. Radiopaque

• Radiolucent materials allow x-ray photons to pass
  through easily (soft tissue).
• Radiopauqe materials are not easily penetrated by
  x-rays (bones)

74
(No Transcript)
75
(No Transcript)
76
(No Transcript)
77
Short Scale vs. Long Scale
78
(No Transcript)
79
(No Transcript)
80
(No Transcript)
81
Radiographic Density