1. X-RAY TUBE & EXPOSURES INVERSE SQ LAW CIRCUITRY
RT A 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

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. How does the “technique” What is it? How does it affect the “image”
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.

13. Producing optimal radiographs

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.

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. Introduction to Technical Factors to Create an image
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 too much x-radiation reached the image receptor
Underexposed
Referring to a radiograph that is too light because too little x-radiation reached the image receptor

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

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
0.001 to 6 seconds

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

39. mAs DOUBLED = DENSITY DOUBLED

41. + 25% % 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

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 % 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

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

66. INTENSITY IS SPREAD OUT…

67. INVERSE SQUARE LAW FORMULA

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

69. INVERSE SQAURE LAW
YOUR TURN
10 QUESTIONS IN CLASS

70. Introduction to Circuitry
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

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
high voltage, low current
low voltage, high current
Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 126. 79
© UW and Brent K. Stewart PhD, DABMP

80. 3 Divisions of Circuit Board
PRIMARY (CONTROL PANEL) yellow
SECONDARY
(HIGH VOLTAGE) blue
FILAMENT
(LOW CURRENT) purple

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 Console
Transformers
Tube

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

87. Circuitry: Source: Carlton & Adler (1996)
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
MAINBREAKER
EXPSOURE SWITCH
AUTOTRANSFORMER
TIMER CIRCUIT
HIGH VOLTAGE STEP UP TRANSFORMER
RECTIFIER
FILAMENT CIRCUIT VARIABLE SELECTPR
FILAMENT STEP DOWN TRANSFORMER
X-RAY TUBE
ROTOR / STATOR

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

94. 5 6 4 7 8 #1 3 9
mA selector 10 2
See Circuitry Review handout and chart for numbers

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

97. © UW and Brent K. Stewart PhD, DABMP
high voltage, low current
Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 126. 97
© UW and Brent K. Stewart PhD, DABMP

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

103. QUESTIONS ?

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 ?