1. Principles of Image Production

3. Focusing cup

4. X-ray Tube
Vacuum tube
A device that relies on the flow of electric current through a vacuum
Glass envelope
Good insulator, vacuum tight, high melting point
Tube housing
Lined with 1.5mm of lead(pb) to prevent leakage radiation

6. Cathode
Negative electrode
Contains
Focusing cup
Filament

7. Cathode
Focusing cup
Focuses the electrons on a smaller spot of the anode
Made of nickel, stainless steel or molybdenum
House the filaments

8. Cathode
Filament
Spiral coil made of Tungsten
Heats up and emits electrons
When rotor/prep is pressed
Dual focus tube houses 2 filaments
Only 1 is charged during x-ray production dependent upon what focal spot size is chosen

9. Apply your knowledge
What control setting does the radiographer set that would affect the number of electrons being released from the heating of the filament?
mA /current
Higher mA= increase in electrons= increase in the amount of x-rays that are produced

10. Anode Positive electrode Electrons strike anode target
Target is made of Tungsten
Stationary or Rotating
Rotating (via induction motor)
Avoids pitting
Large copper rotor
Steel bearings

11. Target Made of Tungsten Angled Line Focus Principle
The angling of the anode results in the effective focal spot being smaller than the actual focal spot
Smaller the angle/smaller the effective FSS
Smaller the angle/smaller the effective FSS

12. Line Focus Principle Actual FSS
Target area on Anode that is exposed to electrons
Effective FSS
Directly under the anode target
Area projected onto patient and IR

13. Actual FSS- Target area on the anode where electrons strike
Actual FSS- Target area on the anode where electrons strike.. Filament chosen determines what type of size stream you will have (Large/Small FSS)
Effective FSS- area projected on the pt and IR. Smaller angle will give you a smaller effective FSS. Tubes are manufactured with specific degrees of angles
To maintain the line focus principle you need a Large actual focal spot size which spreads the heat load (allows for higher exposures) and a small effective focal spot to improve image detail

14. Anode Heel Effect
X-rays are more intense on the cathode side of the tube and less intense toward the anode.
The lowering intensity on the anode side=lighter image on that end
Place thinner or less dense portion of the pts anatomy under anode end (scoliosis series)

15. Thermionic Emission Heat induced flow of electrons
Heated filament emits electrons by thermionic emission
Occurs when you press the rotor/prep button

16. Apply your knowledge
What control setting does the radiographer set that would affect the energy of the electrons as they reach the anode?
kVp- penetration

17. X-ray Production
High speed electrons from Cathode, collide with anode target and loose energy
Xrays are produced
Happens when exposure button is pressed

19. Bremsstrahlung
Occurs when an incident electron interacts w/ the force field of an atomic nucleus.
The force of the nucleus causes the electron to slow down.
As the electron loses energy, it changes direction and the energy loss appears as an x-ray
85% of the x-ray beam consists of this interaction
The electron does not hit anything/ only interacts with the force field

20. e Electromagnetic spectrum Heterogeneous part of the x-ray beam
Heterogeneous/not uniform
Small amount of energy= longer wavelength
Large amount of energy=shorter wavelength
Electromagnetic spectrum
Heterogeneous part of the x-ray beam

21. Wavelengths
A measure of the distance from the peak of one wave to the peak of the next wave
Long wavelength, low frequency

22. Frequency The number of waves that pass a given point per second
Short wavelength, high frequency. A lot more waves passing at a given point. Higher penetration/energy

23. Characteristic Interactions
Projectile electron interacts w/ electron from inner shell(K) of target(tungsten) atom
An outer shell electron drops into the open position & creates an energy difference
The energy difference is emitted as an x-ray
Only K-shell x-rays are diagnostically useful.
Electron hits the inner shell
The only interaction that produces x-ray photons is characteristic interaction
Termed as secondary x-ray radiation/ photon (radiation that is emitted from atoms of an absorber)

25. X-ray Production Source of free electrons (filament/mA) set by mA
Filament heats up based on the amount of current (mA)
Thermionic Emission (step down transformer located in the filament circuit)
Acceleration of Electrons (kVp)
Kilovoltage sent to the filament from the step up transformer
Focusing of electrons
Deceleration of Electrons
4 things needed for x-ray production
Thermionic Emission (put ball on the T)
Acceleration of Electrons (hits ball down field)

26. Apply Your Knowledge What Happens When…………
The rotor/prep button is pressed?
When the exposure button is pressed?
1.Filament current heats up filament and boils off electrons through thermionic emission
2.Cathode repels electrons toward the anode and electrons strike anode. X-rays are produced

27. Maximize Tube Life

29. What are some of the ways a radiographer can help maximize the x-ray tubes life?
In regards to mA, how can we maximize tube life?

30. Maximize tube life Use low mA Tube current/quantity of electrons
High filament current applied for too long will shorten filament life.
Tungsten from the filament is deposited on to the glass envelope.

31. Maximize tube life Make sure tube is warmed up before using
Warm up with low mA exposures
High mA exposures on cold target will crack the target
100mA 1sec kVp Large FS

32. Calculate Heat Unit kVp x mA x S x c 3 phase 6 pulse generator
Follow tube rating charts to prevent excessive heat damage to tube
kVp x mA x S x c
3 phase 6 pulse generator
1.35 x kVp x mA x sec
3 phase 12 pulse generator
1.41 x kVp x mA x sec
S=seconds (time)
C=generator

33. What is the heat unit for a 6 pulse unit set at 70kVp 100mA 1/2sec
4,725 HU

34. 4,725 HU

35. Dark shades-photons that reach the image receptor
Beam Characteristics
Beam Quality- Refers to the penetrating(energy) power of the x-ray beam
Affected by
kVp
Beam filtration
Beam Quantity-Total number(intensity) of x-ray photons in a beam
mAs, kVp, Distance and Filtration
Dark shades-photons that reach the image receptor
X-ray quantity is indirectly related to filtration/ As filtration is increased, quantity will decrease because low energy x-rays will be absorbed by filtration
Penetration refers to the photons that are transmitted through the body and reach the image receptor(result in an image)
Light/clear areas-no photons reached

36. Beam Quality
Penetrating (energy/how fast) power of the beam/kVp is primary factor
Directly proportional to kVp
kVp= beam penetration
High kVp=High quality or “Hard” beams
Low kVp=Low quality or “Soft” beams
Penetration refers to the photons that are transmitted through the body and reach the image receptor(result in an image)
An increase in filtration results in an increase in x-ray quality but not penetrability

37. Beam Quality Filtration
Removes the lower energy photons making the quality higher
Directly related
Half-value layer
Beam quality is measured by the half-value layer
Thickness of absorbing material (AL) necessary to reduce the energy of the beam to ½ its original intensity
Increases beam quality, but not penetrability

38. Beam Quantity Total number of x-ray photons in beam Affected by
mAs, kVp, distance and filtration
mAs is the primary factor
Directly proportional to mAs
Double the mAs=Double output
Square of kVp
Double kVp=increase quantity by factor of four

39. Inverse Square Law
Beam Quantity varies inversely as the square of the distance
Inverse Square Law- The intensity of the beam is inversely proportional to the square of the distance
The intensity quadruples if the distance is reduced to ½ of its original value

40. Apply your knowledge
What will the intensity of a beam be at 40 inches if it is 5 R at 80 inches?
Pg 57 (Johnston & Fauber) 20R

41. X-ray Beam Review Beam Quality kVp (direct)
Filtration(Half Value Layer)(direct)
Beam Quantity
mAs (direct)
kVp (direct but not proportional)
Distance (indirect)
Filtration (Half Value Layer) (indirect)
Sum it up!

42. Beam Characteristics Primary vs. Remnant
Primary radiation- useful radiation that consists of the x-ray photons directed through the x-ray tube window port “Incident Photons”
Remnant radiation- “exit radiation” the portion of the attenuated(progressive absorption) x-ray beam that emerges from the patient and interacts with the image receptor
Primary
X-ray beam prior to interaction w/ the pt
Remnant
Image forming beam

43. Fundamental Properties
X-ray is a form of electromagnetic energy
Heterogeneous and polyenergetic
Wide variety of wavelengths and energies
X-rays travel in straight line at the speed of light
Ionize Matter
Removal of an electron from an atom

44. Fundamental Properties
Ionize Matter
Removal of an electron from an atom
Ionization is the characteristic of x-rays that make them dangerous in general and
harmful to the patient if misused
Damage molecules and DNA, cause chemical changes in cells

45. Photon Interactions with Matter
Purpose: How X-ray photons interact w/ matter(human tissue)
Reason: To minimize harm to the patient and produce a quality radiographic image
X-rays travel in straight line

46. Compton Interaction
Scattering events that ionize the atom
Incident photon interacts w/ an outer- shell electron, producing a scatter photon and recoil electron
Problems
Results in Image fog
Adds to patient dose
Major source of Occupational radiation dose
Incident photon interacts w/ an outer- shell electron, producing a scatter photon and recoil electron

47. Incident photon interacts w/ an outer-shell electron, producing a scatter photon and recoil electron
Ionize the atom

48. Photoelectric Interaction
Total absorption of the incident photon
A characteristic cascade producing secondary photon results
An ejected photoelectron exits the atom w/ enough energy to undergo many more interactions
The atom is ionized
Primary source of patient radiation exposure
Directly impacts contrast
An increase in contrast= increase in pt dose

49. Total absorption of the incident photon
The atom is ionized

50. Coherent (Classical) Interactions
AKA: Coherent Scattering or Thomson Scattering
No electron is removed, the atom absorbs the energy & then releases it in a new direction
Contribute only to patient skin exposure
Very low energy
Unmodified

51. Key Words for Interactions
Interactions that are happening inside the tube
Incident electrons (Bremsstrahlung/Characteristic)
Interacts w/ force field (Bremsstrahlung)
Dislodges a K-shell electron(Characteristic)
Photon interactions w/ matter (human tissue)
Incident photons
Scatter photon (Compton)
Photon- now they have electromagnetic energy

52. Beam Attenuation
Differential absorption

53. The process of image formation is a result of differential absorption of the xray beam as it interacts with anatomic tissue
Anatomic parts do not absorb the primary beam to the same degree

54. Beam Attenuation Gradual loss of intensity
Reduction in energy/number of photons as the beam passes through anatomic tissue
Affected by
Thickness of the anatomic part
Atomic number
Tissue density
Energy of the beam (Quality)

55. Beam Attenuation Tissue Thickness tissue thickness
Increase attenuation
More x-rays are absorbed or scattered by the tissue so more radiation is needed to produce an image

56. Beam Attenuation Atomic Number High atomic number (bone)
Increase attenuation= bright image
Lower atomic number (fat)
Decrease attenuation= light image

57. Beam Attenuation Tissue Density Compactness of the atomic particles
Increase attenuation
Bone Muscle
Muscle Fat
Fat Air

58. Beam Attenuation Quality of the beam Higher penetrating x-rays
Wavelength
shorter
Frequency
higher
Attenuation
decrease

59. Beam Attenuation Lower penetrating x-rays Wavelength longer Frequency
higher

60. Processes that occur during beam attenuation
Absorption
Enough energy to remove an inner-shell electron (ionization)
The ejected electron (photoelectron) has very low energy and will quickly lose the energy by interacting with nearby tissue
Photoelectric effect

61. Processes that occur during beam attenuation
Scattering
Photons that are not absorbed but lose energy
When the incoming photon ejects an outer-shell electron for a tissue atom
Ejected electron is a Compton electron
Remaining lower-energy xray photon changes direction and may leave the part to interact with the image receptor
Provide no useful information/minimize
Compton Interaction

62. Compton or Photoelectric
Higher kVp
Compton
Lower kVp
Photoelectric

63. Transmission
An incoming xray photon passes through the anatomic part without any interaction with the atomic structures and expose the image receptor
Dark shades on the film
Lungs
Absorption- white areas/bright Photons do not reach the image receptor
Transmission – dark areas/greys

64. Transmission
Less than 5% of the primary x-ray beam interacting with the anatomic part actually reches the image receptor
A % less than that is used to create the image
The remnant/exit radiation leaving the patient interacts with an image receptor to create the latent(invisible ) image
Absorption- white areas/bright Photons do not reach the image receptor
Transmission – dark areas/greys

65. Factor Beam attenuation Absorption Transmission
Tissue Thickness
Increase thickness
Decrease thickness
Tissue Atomic Number
Increase number
Decrease number
Tissue Density
Increase density
Decrease density
Xray Beam Quality
Increase Quality
Decreasing Quality