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RT A 2009 WK 5 X-RAY TUBE & EXPOSURES INVERSE SQ LAW CIRCUITRY.

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Presentation on theme: "RT A 2009 WK 5 X-RAY TUBE & EXPOSURES INVERSE SQ LAW CIRCUITRY."— Presentation transcript:

1 RT A 2009 WK 5 X-RAY TUBE & EXPOSURES INVERSE SQ LAW CIRCUITRY

2 Objectives X-ray tube review Properties of X- rays “Prime Factors” Inverse Square Law X-ray Circuit

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4 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

5 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.

6 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.

7 X-Ray Properties Cause fluorescence of certain crystals. Cannot be focused by a lens. Affects photographic film.

8 X-Ray Properties Produce chemical and biological changes in matter through ionization and excitation. Produce secondary and scatter radiation.

9 PRIME FACTORS How does the “technique” What is it? How does it affect the “image”

10 PRIME FACTORS KVP MAS DISTANCE

11 The amount of overall blackening on a radiograph, or of a certain part of the image, is referred to as density. Density results from two things: the amount of radiation that reaches a particular area of the film, and the amount of black metallic silver deposited when the film is developed.

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13 Producing optimal radiographs

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17 How much of the radiation received by the patient Actually reaches the IR ?

18 About 1%

19 Creating the IMAGE When x-rays pass through a patient's body, three things can happen: (1) the x-ray photon is transmitted, passing through the body, interacting with the film, and producing a dark area on the film; (2) the x-ray photon is absorbed in an area of greater tissue density, producing lighter areas on the film; and (3) the x-ray photon is scattered and reaches the film causing an overall gray fog.

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22 Radiographic Prime factors The factors principally responsible for x- ray quality and quantity. These are mAs, kVp, distance (SID).

23 PRIME FACTORS SID - ADJUSTED IN THE ROOM KVP - “intensity of beam” CONTAST RANGE FOR PART MAS – “density of image” CHANGES WITH PT SIZE

24 mAs & kVp Introduction to Technical Factors to Create an image

25 X-ray quantity(mAs) is a measure of the number of x- ray photons in the beam. Also called x-ray output, intensity or exposure. X-ray quality(kVp) is a measure of the penetrating ability of the x-ray beam

26 The quantity of electron flow, or current, in the X-ray tube is described in units of milliamperes (mA). The maximum kinetic energy of the accelerated electrons is defined in terms of kilovolts peak potential (kVp).

27 IMAGES DENSITY = THE AMOUNT OF BLACKENING “DARKNESS” ON THE RADIOGRAPH CONTRAST – THE DIFFERENCES BETWEEN THE BLACKS TO THE WHITES

28 Film Screen Overexposed Referring to a radiograph that is too dark because toomuch x-radiation reached the image receptor Underexposed Referring to a radiograph that is too light because toolittle x-radiation reached the image receptor

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32 Density on Image When a radiologist looks at a radiograph, they looks for any anatomic or pathologic change that causes a change from the normal density. That could be, a solid mass in the lung that stops x-rays from reaching the film and decreases the amount of film darkening in that area (appears “light or white on image” Or excessive “AIR” – looks BLACK

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34 mAs mA X s = mAs

35 Milliamperage mA One milliampere is equal to one thousandth of an ampere. The amount of current supplied to the x-ray tube Range 10 to 1200 mA

36 Tube current (mA) Tube current is equal to the number of electrons flowing from the cathode to the anode per unit time Exposure of the beam for a given kVp and filtration is proportional to the tube current

37 Time In seconds How long x-rays will be produced to 6 seconds

38 mAs Changes at least % mas change needed to see a visible change in density

39 mAs DOUBLED = DENSITY DOUBLED

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41 + 25% + 50 % mAs

42 Kilovoltage Peak kVp One kilovolt is = to 1000 volts The amount of voltage selected for the x-ray tube Range 45 to 120 kVp (diagnostic range) kVp controls contrast

43 Tube voltage (kVp) Determines the maximum energy in the beam spectrum and affects the quality of the output spectrum Efficiency of x-ray production is directly related to tube voltage

44 Contrast- the differences between blacks to whites Kilovolts to anode side – kVp ( ) Kilovolts controls how fast the electrons are sent across the tube kVp – controls CONTRAST on images Low kVp – more absorbed – black - white High kVp - more grays on image

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46 Influencing factors: kVp 15% rule:  15% kVp = doubling of exposure to the film  15% kVp = halving of exposure to the film 15% rule will always change the contrast of the image because kV is the primary method of changing image contrast. Remember : 15% change (  ) KVP has the same effect as doubling or ½ the MAS on density

47 + 15% kvp - 15% kvp

48 CONTROL PANEL CONTROLS kVp SELECTION mA SELECTION TIME (sec.)

49 The Control Console The control console is device that allows the technologist to set technical factors (mAs & kVp) and to make an exposure. Only a legally licensed individual is authorized to energize the console.

50 Control panel

51 X-Ray Machine Purpose: –provide a specific current (mA) & voltage (kV) to the x-ray tube –convert electrical energy to electromagnetic energy (x rays) in a controlled manner control the energy of the x-ray photons control the number of photons

52 kVp & mAs kVp = quality of beam – the “intensity of how much tissue it can penetrate mAs – the amount of time the beam is left on

53 THE X-RAY TUBE The ANODE (+) attracts the electrons that are “boiled off From the --- Negative CATHODE (--)

54 kVp & mAs

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57 kVp = energy mAs = amount

58 HIGH VOLTAGE TO ANODE – ATTRACTS – ELECTRONS FROM CATHODE CURRENT TO STATOR CAUSES ROTATION OF ANODE

59 Rotating Anode

60 INVERSE SQAURE LAW Applies basic rules of geometry The intensity of radiation at a given distance from the point source is inversely proportional to the square of the distance. Doubling the distance decreases intensity by a factor of four.

61 INVERSE SQUARE LAW The inverse square law – Used for RADIATION PROTECTION When you change your distance from the “radiation source” The intensity of radiation will be reduced by a square of the distance (MOVING AWAY FROM THE SOURCE) OR INCREASED – CLOSER TO SOURCE

62 DISTANCE Distance from the radiation source should be kept as great as possible Physical Law: –Inverse Square Law

63 Application of inverse square law principles can yield significant reductions in patient and operator radiation exposure.

64 Inverse square law

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66 INTENSITY IS SPREAD OUT…

67 INVERSE SQUARE LAW FORMULA

68 Inverse Square Law Formula Intensity #1 Intensity #2 Distance #2 - Squared Distance #1 - Squared

69 INVERSE SQAURE LAW YOUR TURN 10 QUESTIONS IN CLASS

70 X-RAY CIRCUITY Introduction to Circuitry Contributions by Mosby, Thompson Publisher, Carlton, Bushberg, and the WWW.

71 How the current gets to the TUBE

72 Current from the outlet

73 Generator+ Transformers (where the power comes from)

74 Review Handouts Circuit Board Symbols Function

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76 AUTOTRANSFORMER RAISES OR LOWERS THE VOLTAGE KVP CONTROL TAPS LOCATED 220 VOLTS INCOMING CONVERTED FROM 100 T0 300 VOLTS

77 AUTOTRANSFORMER

78 TIMER SWITCH Timer switch ends exposure Timer – length of exposure set at control panel

79 © UW and Brent K. Stewart PhD, DABMP 79 Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p low voltage, high current high voltage, low current

80 3 Divisions of Circuit Board

81 TRANSFORMERS (Step Up or Step Down) Increases the VOLTAGE going to the ANODE side of the tube OR 110 volts to 110,000 volts Decreases the CURRENT going to the CATHODE side of the tube 5 Amps to 50 milliamps

82 STEP UP TRANSFORMER

83 X-Ray Tube Circuit

84 Functional Position Control ConsoleTransformersTube

85 Additional practice & preview of next week Circuitry, Inverse square & Interactions

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87 Circuitry: Source: Carlton & Adler (1996). Principles of radiographic imaging: An art and a science. (96-99). MAIN CIRCUIT  Modifies incoming current to produce x-rays  Boosts voltage to range necessary produce x-rays.  Modifies incoming line power to produce thermionic emission from the filament wire. FILAMENT CIRCUIT Filament circuit adjusts to mA ratings (50, 100, 200, etc.). After mA selection, current sent to step down transformer to modify amps that reach filament on x-ray tube

88 Important Parts Of The Circuit Board TO ID 1.MAINBREAKER 2.EXPSOURE SWITCH 3.AUTOTRANSFORMER 4.TIMER CIRCUIT 5.HIGH VOLTAGE STEP UP TRANSFORMER 6.RECTIFIER 7.FILAMENT CIRCUIT VARIABLE SELECTPR 8.FILAMENT STEP DOWN TRANSFORMER 9.X-RAY TUBE 10.ROTOR / STATOR

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92 Now it is your turn Name the parts of the labeled Circuit board

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94 #1# mA selector See Circuitry Review handout and chart for numbers

95 Important Parts Of The Circuit Board TO ID 1 Incoming Line Voltage 2Autotransformer 3 KVP Selector 4Timer No # Ma Selector 5Primary Side (Low Voltage) 6Secondary Side (High Voltage) 7X-ray Tube 8Rectifier 9STEP – Up Transformer 10STEP – Down Transformer

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97 © UW and Brent K. Stewart PhD, DABMP 97 Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p high voltage, low current

98 TRANSFORMERS (Step Up or Step Down) Increases the VOLTAGE going to the ANODE side of the tube OR 110 volts to 110,000 volts Decreases the CURRENT going to the CATHODE side of the tube 5 Amps to 50 milliamps

99 Filament Current Current comes from Autotransformer Controls the Ma selection Focal Spot Selector Switch located here

100 FILAMENT CURRENT

101 MA METER MEASURE THE MA GOING TO THE XRAY TUBE

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103 QUESTIONS ?

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105 A few days after Roentgen's initial public announcement of his discoveries, a doctor in America took X-ray photographs of a person with gunshot wounds in his hands Why can you see the bullet fragments?

106 X-Ray Tube Circuit

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

108 The Electromagnetic Spectrum X-rays have wavelengths much shorter than visible light, but longer than high energy gamma rays.

109 IMAGE CREATION ATOMS INTERACTION WITH “MATTER” ATOMIC NUMBER

110 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.

111 Kinetic energy Energy of motion The electrons KINETIC energy is converted to PHOTON energy

112 Tube Interactions Heat = 99% X-ray = 1% Bremsstrahlung (Brems) = 80% Characteristic = 20%

113 Brems

114 BREMS RADIATION Electron Passes by nucleus Changes direction Energy released as a PHOTON

115 Characteristic

116 CHARACTERISTIC (in tube) Electron hits inner shell e in orbit – knocked out & creates a hole Other E’s want to jump in Energy released as PHOTONS

117 Heat

118 QUESTIONS ?


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