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Raiobiology 9
Raiobiology 9
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Raiobiology 9

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  • Part No...., Module No....Lesson No Module title IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources 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)
  • Part No...., Module No....Lesson No Module title IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources Explanation or/and additional information Instructions for the lecturer/trainer
  • Part No...., Module No....Lesson No Module title IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources Explanation or/and additional information Instructions for the lecturer/trainer
  • Part No...., Module No....Lesson No Module title IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources Lecture notes: ( about 100 words) Instructions for the lecturer/trainer
  • Part No...., Module No....Lesson No Module title IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources 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)
  • Part No...., Module No....Lesson No Module title IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources 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)
  • Part No...., Module No....Lesson No Module title IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources 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)
  • Part No...., Module No....Lesson No Module title IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources 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)
  • Part No...., Module No....Lesson No Module title IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources 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)
  • Part No...., Module No....Lesson No Module title IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources 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)
  • Part No...., Module No....Lesson No Module title IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources 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 120.000 HU, it will take  5 min to cool down completely
  • Part No...., Module No....Lesson No Module title IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources 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)
  • Part No...., Module No....Lesson No Module title IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources
  • Transcript

    • 1. RADIOBIOLOGY Prof.Dr.Tarek Elnimr L 9 Presented to the Biology Departments in Faculty of Sciences on February 15 , 2009
    • 2. L 9: X Ray production
    • 3. 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
      6: X Ray production
    • 4. Topics
        • Basic elements of an X Ray source assembly
        • Cathode structure
        • Anode structure
        • Rating chart
        • X Ray generator
        • Automatic exposure control
      6: X Ray production
    • 5. Overview
      • To become familiar with the technological principles of the X Ray production
      6: X Ray production
    • 6. Part 6: X Ray production Topic 1: Basic elements of an X Ray source assembly IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
    • 7. 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
    • 8. X Ray tubes 6: X Ray production
    • 9. 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
    • 10. X Ray tube components 6: X Ray production 1: long tungsten filament 2 : short tungsten filament 3 : real size cathode 1: mark of focal spot housing cathode
    • 11. Part 6: X Ray production Topic 2: Cathode structure IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
    • 12. 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
    • 13. Example of a cathode 6: X Ray production
    • 14.
      • 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 !
      Cathode structure (I) 6: X Ray production
    • 15. Part 6: X Ray production Topic 3: Anode structure IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
    • 16. 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
    • 17. 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
    • 18. Anode characteristic 6: X Ray production 1 : anode track 2 : anode track
    • 19. Anode angle (II) 6: X Ray production THE SMALLER THE ANGLE THE BETTER THE RESOLUTION  Angle Incident electron beam width Apparent focal spot size Actual focal spot size Film  Angle Incident electron beam width Increased apparent focal spot size Actual focal spot size Film ‘  
    • 20. 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
    • 21.
      • 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
      Anode heel effect (II) 6: X Ray production
    • 22. 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
    • 23. Part 6: X Ray production Topic 4: Rating Chart IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
    • 24. 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
    • 25. 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
    • 26.
      • 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 )
      X Ray tube rating chart (II) 6: X Ray production
    • 27. X Ray tube rating chart (III) 6: X Ray production 0.01 0.05 0.1 0.5 1.0 5.0 10.0 700 600 500 400 300 200 100 50 kVp 70 kVp 90 kVp 120 kVp Unacceptable Exposure time (s) Tube current (mA) X Ray tube A  half-wave rectified 3000 rpm 90 kV 1.0 mm effective focal spot
    • 28. X Ray tube rating chart (IV) 6: X Ray production 0.01 0.05 0.1 0.5 1.0 5.0 10.0 700 600 500 400 300 200 100 50 kVp 70 kVp 90 kVp 125 kVp Acceptable Exposure time (s) Tube current (mA) X Ray tube B 3  full-wave rectified 10.000 rpm 125 kV 1.0 mm effective focal spot Unacceptable
    • 29. 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 120.000 HU, it will take  5 min to cool down completely
      6: X Ray production
    • 30. Anode cooling chart (II) 6: X Ray production 240 220 200 180 160 140 120 100 80 60 40 20 Elapsed time (min) Heat units stored (x 1000) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 500 HU/sec 1000 HU/sec 350 HU/sec 250 HU/sec Imput curve Cooling curve Maximum Heat Storage Capacity of Anode
    • 31. Part 6: X Ray production Topic 5: X Ray generator IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
    • 32. 6: X Ray production 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)
    • 33. 6: X Ray production
      • 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 = k 0 . U n . I . T
        • U : peak voltage (kV)
        • I : mean current (mA)
        • T : exposure time (ms)
        • n : ranging from about 1.5 to 3
      X-ray generator (II)
    • 34. 6: X Ray production
      • 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 : 140 - 150 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 - U min )/U] x 100%
      X-ray generator (III)
    • 35. 6: X Ray production 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”
    • 36. 6: X Ray production 100% 13% 4% Line voltage Single phase single pulse Single phase 2-pulse Three phase 6-pulse Three phase 12-pulse 0.02 s 0.01 s kV ripple (%) Tube potential wave form (II)
    • 37. 6: X Ray production 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
    • 38. 6: X Ray production
      • 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
      The choice of the number of pulses (II)
    • 39. Part 6: X-ray production Topic 6: Automatic Exposure Control (AEC) IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
    • 40. 6: X Ray production 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
    • 41. 6: X Ray production Automatic exposure control X Ray tube Collimator Beam Soft tissue Bone Air Patient Table Grid Cassette AEC detectors
    • 42. 6: X Ray production 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
    • 43. Part 6: X-ray production Topic 7: X-ray equipment operation and mode IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
    • 44. 6: X Ray production 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 : 50 - 70 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 300 - 500 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
    • 45. 6: X Ray production 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 : 40 kW @ 0.6 focus size for spot film
          • output : 70 kW @ 1.0 for fluoroscopy (high resolution)
          • priority given to contrast
          • automatic settings of kV
      • Cardiac angiography
        • Three phase generator - continuous output  1kW
          • output : 30 kW @ 0.4 focus size
          • output : 80 kW @ 0.8 focus size
          • frame rate : up to 120 fr/s
    • 46. 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
      6: X Ray production
    • 47. 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

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