1. RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY
Part No...., Module No....Lesson No
Module title
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY
L 6: X Ray production
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

2. Part No...., Module No....Lesson No
Module title
Introduction
A review is made of:
The main elements of the of X Rays tube: cathode and anode structure
The technology constraints of the anode and cathode material
The rating charts and X Ray tube heat loading capacities
Explanation or/and additional information
Instructions for the lecturer/trainer
6: X Ray production
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

3. Part No...., Module No....Lesson No
Module title
Topics
Basic elements of an X Ray source assembly
Cathode structure
Anode structure
Rating chart
X Ray generator
Automatic exposure control
Explanation or/and additional information
Instructions for the lecturer/trainer
6: X Ray production
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

4. Part No...., Module No....Lesson No
Module title
Overview
To become familiar with the technological principles of the X Ray production
Lecture notes: ( about 100 words)
Instructions for the lecturer/trainer
6: X Ray production
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

5. Part No...., Module No....Lesson No
Module title
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 6: X Ray production
Topic 1: Basic elements of an X Ray source assembly
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

6. Basic elements of the X Ray source assembly
Generator : power circuit supplying the required potential to the X Ray tube
X Ray tube and collimator: device producing the X Ray beam
6: X Ray production

7. X Ray tubes
6: X Ray production

8. X Ray tube components
Cathode: heated filament which is the source of the electron beam directed towards the anode
tungsten filament
Anode (stationary or rotating): impacted by electrons, emits X Rays
Metal tube housing surrounding glass (or metal) X Ray tube (electrons are traveling in vacuum)
Shielding material (protection against scattered radiation)
6: X Ray production

9. X Ray tube components housing cathode 1: long tungsten filament
2 : short tungsten filament
3 : real size cathode
1: mark of focal spot
6: X Ray production

10. Part No...., Module No....Lesson No Topic 2: Cathode structure
Module title
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 6: X Ray production
Topic 2: Cathode structure
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

11. Cathode structure (I)
Cathode includes filament(s) and associated circuitry
tungsten material : preferred because of its high melting point (3370°C)
slow filament evaporation
no arcing
minimum deposit of W on glass envelope
To reduce evaporation the emission temperature of the cathode is reached just before the exposure
in stand-by, temperature is kept at ± 1500°C so that 2700°C emission temperature can be reached within a second
6: X Ray production

12. Example of a cathode
6: X Ray production

13. Cathode structure (I) Modern tubes have two filaments
a long one : higher current/lower resolution
a short one : lower current/higher resolution
Coulomb interaction makes the electron beam divergent on the travel to the anode
lack of electrons producing X Rays
larger area of target used
focal spot increased  lower image resolution
Focalisation of electrons is crucial !
6: X Ray production

14. Part No...., Module No....Lesson No Topic 3: Anode structure
Module title
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 6: X Ray production
Topic 3: Anode structure
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

15. X Ray tube characteristics
Anode mechanical constraints
Material : tungsten, rhenium, molybdenum, graphite
Focal spot : surface of anode impacted by electrons
Anode angle
Disk and annular track diameter (rotation frequency from 3,000 to 10,000 revolutions/minute)
Thickness  mass and material (volume)  heat capacity
Anode thermal constraints
Instantaneous power load (heat unit)
Heat loading time curve
Cooling time curve
6: X Ray production

16. This conflict is solved by slanting the target face
Anode angle (I)
The Line-Focus principle
Anode target plate has a shape that is more rectangular or ellipsoidal than circular
the shape depends on :
filament size and shape
focusing cup’s and potential
distance between cathode and anode
Image resolution requires a small focal spot
Heat dissipation requires a large spot
This conflict is solved by slanting the target face
6: X Ray production

17. Anode characteristic 1 : anode track 2 : anode track
6: X Ray production

18. THE BETTER THE RESOLUTION
Anode angle (II) 
Angle ‘  
Angle
Actual focal
spot size
Actual focal
spot size
Incident electron
beam width
Incident electron
beam width
Increased
apparent
focal spot size
Apparent focal spot size
Film
Film
THE SMALLER THE ANGLE
THE BETTER THE RESOLUTION
6: X Ray production

19. Anode heel effect (I)
Anode angle (from 7° to 20°) induces a variation of the X Ray output in the plane comprising the anode-cathode axis
Absorption by anode of X photons with low emission angle
The magnitude of influence of the heel effect on the image depends on factors such as :
anode angle
size of film
focus to film distance
Anode aging increases heel effect
6: X Ray production

20. Anode heel effect (II) The heel effect is not always a negative factor
It can be used to compensate for different attenuation through parts of the body
For example:
thoracic spine (thicker part of the patient towards the cathode side of the tube)
mammography
6: X Ray production

21. Focal spot size and imaging geometry
Focal spot finite size  image unsharpened
Improving sharpness  small focal spot size
For mammography focal spot size  0.4 mm nominal
Small focal spot size  reduced tube output (longer exposure time)
Large focal spot allows high output (shorter exposure time)
Balance depends on organ movement (fast moving organs may require larger focus)
6: X Ray production

22. Part No...., Module No....Lesson No Topic 4: Rating Chart
Module title
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 6: X Ray production
Topic 4: Rating Chart
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

23. Heat loading capacities
A procedure generates an amount of heat depending on:
kV used, tube current (mA), length of exposure
type of voltage waveform
number of exposures taken in rapid sequence
Heat Unit (HU) [joule] :
unit of potential x unit of tube current x unit of time
The heat generated by various types of X Ray circuits are:
1 phase units : HU = kV x mA x s
3 phase units, 6 pulse : HU = 1.35 kV x mA x s
3 phase units, 12 pulse: HU = 1.41 kV x mA x s
6: X Ray production

24. X Ray tube rating chart (I)
Tube cooling characteristics and focal spot size
 {mA - time} relationship at constant kV
intensity decreases with increasing exposure time
intensity increases with decreasing kV
Note: higher power  reduced exposure time  reduced motion unsharpness
6: X Ray production

25. X Ray tube rating chart (II)
Manufacturers combine heat loading characteristics and information about the limits of their X Ray tubes in graphical representations called Tube Rating Charts
Example:
Tube A: a 300 mA, 0.5 s, 90 kV procedure would damage the system operated from a 1-phase half wave rectified generator (unacceptable)
Tube B: a 200 mA, 0.1 s, 120 kV procedure comply with the technical characteristics of the system operated from a 3-phase fully rectified generator (acceptable)
6: X Ray production

26. X Ray tube rating chart (III)
Part No...., Module No....Lesson No
Module title
X Ray tube rating chart (III)
X Ray tube A
1 f half-wave rectified
3000 rpm 90 kV
1.0 mm effective focal spot
700
600
500
400
300
200
100
70 kVp
Tube current (mA)
50 kVp
Unacceptable
120 kVp
90 kVp
As can be seen a 300 mA, 0.5 s, 90 kV procedure would damage the system operated from a 1  half wave rectified generator (unacceptable) while (next slide)
a 200 mA, 0.1 s, 120 kV procedure comply with the technical characteristics of the system operated from a 3  fully rectified generator (acceptable)
0.01
0.05
0.1
0.5
1.0
5.0
10.0
Exposure time (s)
6: X Ray production
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

27. X Ray tube rating chart (IV)
Part No...., Module No....Lesson No
Module title
X Ray tube rating chart (IV)
700
600
500
400
300
200
100
X Ray tube B
3f full-wave rectified
rpm 125 kV
1.0 mm effective focal spot
70 kVp
50 kVp
Tube current (mA)
90 kVp
Unacceptable
125 kVp
As can be seen a 200 mA, 0.1 s, 120 kV procedure comply with the technical characteristics of the system operated from a 3  fully rectified generator (acceptable)
Acceptable
0.01
0.05
0.1
0.5
1.0
5.0
10.0
Exposure time (s)
6: X Ray production
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

28. Anode cooling chart (I)
Heat generated is stored in the anode, and dissipated through the cooling circuit
A typical cooling chart has:
input curves (heat units stored as a function of time)
anode cooling curve
The following graph shows that:
a procedure delivering 500 HU/s can go on indefinitely
if it is delivering 1000 HU/s it has to stop after 10 min
if the anode has stored HU, it will take  5 min to cool down completely
6: X Ray production

29. Anode cooling chart (II)
Part No...., Module No....Lesson No
Module title
Anode cooling chart (II)
Maximum Heat Storage Capacity of Anode
240
220
200
180
160
140
120
100 80 60 40 20
1000 HU/sec
Imput curve
500 HU/sec
350 HU/sec
Heat units stored (x 1000)
250 HU/sec
The graph shows that :
a procedure delivering 500 HU/s can go on indefinitely
if it is delivering 1000 HU/s it has to stop after 10 min
if the anode has stored HU, it will take  5 min to cool down completely
Cooling curve
Elapsed time (min)
6: X Ray production
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

30. Part 6: X Ray production Topic 5: X Ray generator
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 6: X Ray production
Topic 5: X Ray generator

31. It supplies the X-ray tube with :
X-ray generator (I)
It supplies the X-ray tube with :
 Current to heat the cathode filament
 Potential to accelerate electrons
 Automatic control of exposure (power application time)
 Energy supply  1000  X-ray beam energy (of which 99.9% is dissipated as thermal energy)
6: X Ray production

32. X-ray generator (II)
Generator characteristics have a strong influence on the contrast and sharpness of the radiographic image
The motion unsharpness can be greatly reduced by a generator allowing an exposure time as short as achievable
Since the dose at the image plane can be expressed as:
D = k0 . Un . I . T
U: peak voltage (kV)
I: mean current (mA)
T: exposure time (ms)
n: ranging from about 1.5 to 3
6: X Ray production

33. X-ray generator (III)
Peak voltage value has an influence on the beam hardness
It has to be related to medical question
What is the anatomical structure to investigate ?
What is the contrast level needed ?
For a thorax examination : kV is suitable to visualize the lung structure
While only 65 kV is necessary to see bone structure
The ripple “r” of a generator has to be as low as possible
r = [(U - Umin)/U] x 100%
6: X Ray production

34. Tube potential wave form (I)
Conventional generators
single  1-pulse (dental and some mobile systems)
single  2-pulse (double rectification)
three  6-pulse
three  12-pulse
Constant potential generators (CP)
HF generators (use of DC choppers to convert 50Hz mains into voltages with frequencies in the kHz range)  “Inverter technology”
6: X Ray production

35. Tube potential wave form (II)
Single phase single pulse
kV ripple (%)
100%
Single phase 2-pulse
13%
Three phase 6-pulse 4%
Three phase 12-pulse
Line voltage
0.01 s
0.02 s
6: X Ray production

36. The choice of the number of pulses (I)
Single pulse : low power (<2 kW)
2-pulse : low and medium power
6-pulse : uses 3-phase mains, medium and high power (manual or automatic compensation for voltage drop)
12-pulse : uses two shifted 3-phase system, high power up to 150 kW
6: X Ray production

37. The choice of the number of pulses (II)
CP : eliminates any changes of voltage or tube current
high voltage regulators can control the voltage AND switch on and off the exposure
voltage can be switched on at any moment (temporal resolution)
kV ripple <2% thus providing low patient exposure
HF : combines the advantages of constant potential and conventional generator
reproducibility and consistency of tube voltage
high frame rate possible
6: X Ray production

38. Part 6: X-ray production
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 6: X-ray production
Topic 6: Automatic Exposure Control (AEC)

39. Automatic exposure control
Optimal choice of technical parameters in order to avoid repeated exposures (kV, mA)
Radiation detector behind (or in front of) the film cassette (with due correction)
Exposure is terminated when the required dose has been integrated
Compensation for kVp at a given thickness
Compensation for thickness at a given kVp
6: X Ray production

40. Automatic exposure control
X Ray tube
Collimator
Beam
Soft
tissue
Bone
Air
Patient
Table
Grid
Cassette
AEC detectors
6: X Ray production

41. Automatic exposure control
Optimal choice of technical parameters in order to avoid repeated exposures (kV, mA)
Radiation detector behind (or in front of) the film cassette (with due correction)
Exposure is terminated when the required dose has been integrated
Compensation for kVp at a given thickness
Compensation for thickness at a given kVp
6: X Ray production

42. Part 6: X-ray production
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 6: X-ray production
Topic 7: X-ray equipment operation and mode

43. X-ray equipment operation mode and application (II)
Radiography and Tomography
Single and 3  generators (inverter technology)
output : 30 kW at 0.3 focus spot size
output : kW at 1.0 focus spot size
selection of kV and mAs , AEC
Radiography and Fluoroscopy
Under couch equipment, three  generator (inverter technology) - continuous output of W
output : 50 kW at 1.0 focus size for spot film
output : 30 kW at 0.6 for fluoroscopy (high resolution)
priority given to contrast
automatic settings of kV
6: X Ray production

44. X-Ray equipment operation mode and application (III)
Radiography and Fluoroscopy
Over couch equipment, three phase generator (inverter technology) - continuous output of at least 500 W
output : focus size for spot film
output : for fluoroscopy (high resolution)
priority given to contrast
automatic settings of kV
Cardiac angiography
Three phase generator - continuous output  1kW
output : focus size
output : focus size
frame rate : up to 120 fr/s
6: X Ray production

45. Part No...., Module No....Lesson No
Module title
Summary
The main parts of the system contributing to the desired X Ray production:
provide the required source of power
deliver an appropriate X Ray spectrum
ensure the optimum adjustment of exposure to warrant the image quality
Let’s summarize the main subjects we did cover in this session. (List the main subjects covered and stress again the important features of the session)
6: X Ray production
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

46. Where to Get More Information
Part No...., Module No....Lesson No
Module title
Where to Get More Information
Equipment for diagnostic radiology, E. Forster, MTP Press, 1993
IPSM Report 32, part 1, X-ray tubes and generators
The Essential Physics of Medical Imaging, Williams and Wilkins. Baltimore:1994
Manufacturers data sets for different X Ray tubes
6: X Ray production
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources