1. Principles of Image Production

6. Thermionic Emission-Heat induced flow of electrons
Line Focus Principle-Actual FSS and Effective FSS
Bremsstrahlung Effect-Break in radiation that produces x-rays

7. Focusing cup

8. 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

10. Cathode
Negative electrode
Contains
Focusing cup
Filament

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

12. 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

13. 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
Higher mA= increase in electrons= increase in the amount of x-rays that are produced

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

15. 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

16. 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

17. Actual FSS- Target area on the anode where electrons strike
Effective FSS- area projected on the pt and IR
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
The size of the actual focal spot depends on the size of the cathode filament being used

18. 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)

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

20. 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

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

22. 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

24. 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

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

26. Frequency The number of waves that pass a given point per second
Short wavelength, high frequency

27. 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)

29. 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)

30. 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

31. Maximize Tube Life

33. 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?

34. 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.

35. 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

36. Calculate Heat Unit kVp x mA x T 3 phase 6 pulse generator
Follow tube rating charts to prevent excessive heat damage to tube
kVp x mA x T
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

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

38. 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

39. Beam Quality Penetrating (energy/how fast) power of the beam
Affected by kVp and filtration
Directly proportional to kVp
kVp= beam penetration
High kVp=High quality or “Hard” beams
Low kVp=Low quality or “Soft” beams
kVp is primary factor
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

40. Beam Quality Filtration
Removes the lower energy photons making the quality higher
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

41. 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

42. 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

43. Apply your knowledge
What will the intensity of a beam be at 40 inches if it is 5 R at 80 inches?
A radiographer receives 120 mrem of exposure standing 5feet from the radiation source. If the radiographer wants to decrease his exposure to 50mrem, how far from the radiation source must he stand?
A chest radiograph is produced w/ sufficient optical density using 10mAs at 72 inches. If the same radiograph is performed at 44 SID , what new mAs should be used to produce the radiograph with the same density?
Pg 57 (Johnston & Fauber) 20R
Pg D-22 in Kettering book 7.5feet
Pg D-32 in Kettering book 3.7mAs

44. X-ray Beam Beam Quality kVp Filtration(Half Value Layer) Beam Quantity
mAs
Distance
Filtration (Half Value Layer)
Sum it up!

45. 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

46. 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

47. 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

48. 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

49. 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

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

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

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

53. 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

54. 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

55. Beam Attenuation
Photon- now they have electromagnetic energy

56. Beam Attenuation Gradual loss of intensity Affected by
Thickness of the anatomic part
Atomic number
Tissue density
Energy of the beam (Quality)

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

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

59. Beam Attenuation Tissue Density Compactness of the atomic particles
in tissue density= attenuation
Bone Muscle
Muscle Fat
Fat Air

60. Beam Attenuation Quality of the beam
Higher penetrating x-rays (shorter wavelength w/ higher frequency) =lower attenuation
Lower penetrating x-rays (longer wavelength w/ lower frequency)=higher attenuation