1. Equipment Operation & Maintenance
Review
Equipment Operation & Maintenance

2. ARRT Section Components
30 Questions
Radiographic Equipment (21)
Evaluation of Radiographic Equipment & Accessories (9)

3. X-ray Tube Construction
Vacuum diode tube
cathode
anode
Radiographic Equipment

4. X-ray Tube ConstructionD F C G E
WHAT TYPE OF MOTOR IS ROTOR?
The energy of electrons comprising the tube current is measured in ______________ ?
Radiographic Equipment

5. Cathode - Filaments Negative Electrode Tungsten with thorium
Filament circuit heats (>2200°C) with 3-5 amps
Thermionic Emission
Vaporization
Space charge
Saturation current
Focusing cup

6. Filament I vs. mA Heated filament emits electrodes
Once emission starts small  in filament I = large  in mA
As kVp rises less filament I needed to reach mA

7. Saturation Current/Voltage
Stabilization at specific mA above ~40 kVp

8. Focusing Cup

9. Anodes - Target Rotating Anodes 2” to 5” disk (focal track)
Induction motor
Speed 3000 to rpm Cu
Molybdenum or
Graphite base W Cu W
Other target materials
Tungsten-rhenium
Molybdenum
Rhodium

10. What makes the Anode spin?
Electromagnetic Induction Motor
How fast does it turn?
______________ rpm

11. A motor is a device that converts
electrical energy into mechanical energy

12. Line-Focus Principle Effective FS < actual FS Small angle =  FS
Beveled anode
Improves heat capacity
Small angle =  FS
Small FS =  resolution
AHE 
Field coverage 
Heat loading on smaller anode surface area

13. © UW and Brent K. Stewart PhD, DABMP
Anode Angle and Focal Spot Size (1)
Anode angle < range:
7° - 20°
Why are anodes beveled?
1. Line focus principle (foreshortening of focal spot length)
Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p
© UW and Brent K. Stewart PhD, DABMP

14. © UW and Brent K. Stewart PhD, DABMP
Anode Angle and Focal Spot Size
1. ↓ <→ ↓ apparent focal spot size (B and C)
Smaller the angle – smaller the effective focal spot
2. ↑ <→ ↑ heat loading:
3. ↑ <→ ↑ field coverage (B and C)
Actual < used trade-off of these factors
Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p 14
© UW and Brent K. Stewart PhD, DABMP

15. Anode Angles and Heat Smaller the angle = more heat load
Larger angle – less heat load
Different anode angles are used for different types of equipment:
Diagnostic vs special procedures

16. Which anode angle has greater heat load?

17. ANODE HEEL EFFECT MORE PRONOUNCED WITH SMALLER ANODE ANGLE
(sm anode angle = larger heel effect)
120% ~75% difference of intensity across beam
How does this affect positioning?
FAT – CAT HIGHER AT CATHODE
See pg 139 Bushong

18. A. AP Thoracic Spine B. AP. Lumbar Spine C. Lateral Femur D. AP FOOT
Which of the following projections would take advantage of the anode heel effect on a hyperstenic patient - if the anode was towards the patient’s head?
A. AP Thoracic Spine
B. AP. Lumbar Spine
C. Lateral Femur
D. AP FOOT

19. © UW and Brent K. Stewart PhD, DABMP
X-ray Tube Anode Configuration
Tungsten anode disk
Mo and Rh for mammography
Stator and rotor make up the induction motor
Rotation speeds
Low: 3,000 – 3,600 rpm
High: 9,000 – 10,000 rpm
Molybdenum stem (poor heat conductor) connects rotor with anode to reduce heat transfer to rotor bearings
Anode cooled through transmission
Focal track area (spreads heat out over larger area than stationary anode configuration)
Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 107. 19
© UW and Brent K. Stewart PhD, DABMP

20. © UW and Brent K. Stewart PhD, DABMP
Heel Effect
Reduction of x-ray beam intensity towards the anode side of the x-ray field
Although x-rays generated isotropically
Self-filtration by the anode and the anode bevel causes
Greater intensity on the cathode side of the x-ray field
Can use to advantage, e.g., PA chest exposure
Orient chest to anode side
Abdomen to cathode side
Less pronounced as SID ↑
Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 112. 20
© UW and Brent K. Stewart PhD, DABMP

21. © UW and Brent K. Stewart PhD, DABMP
X-ray Filtration
Filtration: x-ray attenuation as beam passes through a layer of material
Inherent (glass or metal insert at x-ray tube port) and added filtration (sheets of metal intentionally placed in the beam)
Added filters absorb low-energy x-rays and reduce patient dose (↑ beam quality)
HVL – half value layer (mm Al)
Curry, et al., Christensen’s Physics of Diagnostic Radiology, 4th ed., pp. 89, 91. 21
© UW and Brent K. Stewart PhD, DABMP

22. Voltage generators (power supply)

23. Extra-focal Radiation
Miscellaneous Terms
Off Focus Radiation
Protective Housing
Extra-focal Radiation
rebounding e-
Leakage Radiation
<100 1 m

24. OFF FOCUS RADIATION

27. SHADOW OF
SOMEONE’S HEAD =
OFF FOCUS FROM TUBE

29. LEAKAGE RADIATION may not EXCEED
TUBE HOUSING 100mR / HR
@ 1 meter

30. Tube Failures & Prevention
Warm up tube before use
Avoid “boost & hold” exposures if possible
Use acceptable levels of exposure (e.g. tube rating charts)
Failure Causes
Anode pitting/cracking after single excessive exposure
Bearing damage from numerous long exposures
Vaporization of the filament
Filament break
Coating of glass envelope with tungsten

31. Tube Rating Charts (mA)

32. Tube Rating Charts (kVp)

33. Heat Units
HU – measure of thermal energy applied to the x-ray tube from an exposure
Formula based on generator
HU1Ø = kVp x mAs
HU3Ø6p = kVp x mAs x 1.35
HU3Ø12p = kVp x mAs x 1.41
If multiple, consecutive exposures made,
HUT = HU x #exposures

34. Anode Cooling Chart

35. Name 3 types of rectifiers

36. Rectification  AC to DC Keeps e- flowing from cathode to anode
HVT
tube
 AC to DC
Keeps e- flowing from cathode to anode
Uses rectifying bridge between HVT & tube AC
bridge DC
HVT
tube

37. SOLID STATE - DIODES – Semi Conductor
Allows current to only flow in one direction
Most common type used in rectifiers

38. AEC Operation Exit vs. Entrance Select sensor(s) Select density level
Set back-up time
Set kVp
film
Ion chambers
film
Fluorescent
screen
Exposure
Switch
PMT
Exit vs. Entrance

39. Beam Restrictors
Collimator
Cone
Diaphragm

40. Important Circuit ElementsHV
subcircuit
Power
Source
X-ray
Tube
autotransformer
Filament
subcircuit

42. X-ray Generator Transformers Rectification Connection to tube
cathode
Transformers
HV (step-up)
Filament (step down)
Rectification
Connection to tube
anode F
diodes HV

43. Transformers Autotransformer HV Filament Step-up or step-down
Variable TR
Controls kV by varying V sent to HVT HV
Step-up
Fixed TR > 1 (500 to 1000)
VS > VP
 V to kV
Filament
Step-down
Fixed TR < 1
IS > IP (VS<VP)
I in filament to cause e- emission

45. Transformer Review Turns Ratio Transformer Law Power Step Up Step Down

47. Autotransformer – Self Induction
There is only one wire – but works like when there are 2 wires =
The windings are used as the primary and secondary coils
The induced voltage varies on where the outside wires are connected (KVP Taps)

48. TRANSFORMER FORMULAS (STEP UP OR DOWN)
V = voltage
N = # turns
p = primary
s = secondary
I = current
Vp = N p
Vs Ns
Vp = I s
Vs Ip
Np = I s
Ns Ip

49. Transformer Efficiency
By design
Shell – most
Closed core
Open core
Air core
Ideal – no loss
Reality best = ~95% induction
Loss due to
Cu resistance
 wire diameter
Eddy currents
Laminate core
Hysteresis
 core mag. perm.

50. Rectification  AC to DC Keeps e- flowing from cathode to anode
HVT
tube
 AC to DC
Keeps e- flowing from cathode to anode
Uses rectifying bridge between HVT & tube AC
bridge DC
HVT
tube

51. Phase, Pulse & Frequency
Type
# of rectifiers
% ripple
Wave form
1(self) 1 60
100%
1(half)
1 or 2
1(full) 2
120 4
36p 6
360
6 or 12
12-15%
312p 12
720
3-5%
High
Freq.
10kHz
<1% + - + - + - + - + -

52. GENERATOR THAT CREATE AN ALTERNATING CURRENT ARE CALLED:
AN ALTERNATOR –
What does the generator do? CONVERT MECHANICAL ENERGY INTO ELECTRICITY

54. WHAT MEASURES ELECTRIC POTIENTAL = VOLT
CURRENT = AMP
ELECTRIC CIRCUIT IS THE PATHWAY FOR ELECTRIC CURRENT

55. What does a MOTOR due Converts ___________ energy To

56. OHMS LAW V = IR
V = POTIENTAL
A = AMPS (CURRENT)
R = RESISTANCE (OHMS)

57. OHM’S LAW: V = Potential difference in volts I = Current in amperes
R = Resistance in ohms ()
V= IR I =V/R R=V/I

58. Simple SERIES Circuit

59. Series Circuit Rules: Current: IT = I1 =I2 =I3
Voltage: VT = V1 + V2 + V3
Resistance:
RT = R1 + R2 + R3

60. Parallel Circuit Rules
Current:
IT = I1 + I2 + I3
Voltage:
VT = V1 = V2 = V3
Resistance:
RT = R1 + R2 + R3
(REMEMBER TO FLIP SIDES RT/1

62. TYPES OF EQUIPMENT
FIXED
MOBILE
DEDICATED
MAMMO , CHEST, HEAD

65. EXPOSURE SWITCH
TIMER

66. RHEOSTAT VAIRIABLE REISITOR
regulate the amount of resistance in a circuit

68. What makes the Anode spin?
Electromagnetic Induction Motor
How fast does it turn?
______________ rpm