X-ray tube failures and its care

1. {
FAULTS IN X-RAY TUBE
AND ITS CARE
PRESENTED BY
Saru Gosain
BSc.MIT 2nd year
(2017)

2. COMMON CAUSES OF
TUBE FAILURE
• Extremely high voltage
• Excessive heat generation
• Poor cooling system
• Rough-handling/ Careless
• Aging

3. COMMON FAULTS, THEIR
CAUSES & REMEDY
A. FAULTS IN X-RAY TUBE
HOUSING
1. Cracking of x-ray tube
housing
 Escape of oil from the housing
 Insulation level &Cooling rate
are reduced
Causes
• Expansion of air & oil present
inside it and increased in its
internal pressure.
Remedy
• Excluding air
• Use of metal bellows to allow oil
expansion as well as to operate
as “microswitch”

4. Leakage oil testing devices

5. Cont.…
2. Radiation leakage
 Increases patient’s as well as
personnel radiation dose.
 Should not exceed 100 mR/hr
at 1m
Causes
• Cracking of the tube housing
• Improper shielding
Remedy
• Proper shielding should be
done .
• Replace the tube with new
one as soon as possible.

6. Cont.…
B. FAULTS IN GLASS/METAL
ENVELOPE
1. Loss of vacuum
 Production of secondary electrons
 Result in the variation in the number,
reduced speed of electrons impinging
on the target, energy of x-ray
produced
 Production couldn’t be controlled
independently.
Causes
• Crazing of the glass enclosure due to
difference in coefficients of expansion
of glass and metal
• Inactivity

7. Cont.…
Remedy
 Use of special alloys having the
same coefficients of linear
expansion as Pyrex glass are used.
C. FAULTS IN FILAMENT
1. Vaporization of filament
a) Breakage of filament
 No exposure takes place
Causes
• Excessive heating of filament for
the longer period of time

8. Cont.…
Remedy
• Use of automatic filament-boosting
circuit
• Use of 1-2 % Thorium with tungsten
filament
b) Tube arcing
 Produces a bronzed
-colored “sunburn” color
 Filters the x-ray beam
 “Crazing” of the tube
Causes
• Evaporation of the filament
Remedy
• Use of metal enclosure instead of
glass enclosure

9. Cont.…
D. FAULTS IN ANODE
1. Kinking of the target material
 Results in distortion of the anode angle, narrowing of the
beam, greater geometric unsharpness.
Causes
• Difference in thermal expansion of metal on the surface
& metal immediately beneath the surface.
Remedy
• 10% Rhenium is added to 90% of tungsten target
• Manufacture anode disc with slits in the target surface to
allow the material in the focal track to expand without
producing the mechanical tension.

10. Cont….
2. Roughening and pitting of anode surface
 Scattering of the x-rays
 Absorption of x-rays by the
target itself.
 Results in diminish x-ray output
Cause
• Excessive thermal stress
Remedy
• Use of lowest necessary power
• Largest possible focal spot
• Longer exposures at reduced power
For

11. FIGURE 6-14 Comparison of smooth, shiny appearances of rotating anodes when new (A) versus
their appearance after failure
(B–D). Examples of anode separation and surface melting shown were caused by slow rotation
caused by bearing damage (B),
repeated overload (C), and exceeding of maximum heat storage capacity (D). (Courtesy Philips
Medical Systems.)
A B
C D

12. Cont….
3. Imbalance ball bearings
 Jamming
 Increased bearing noise
 Anode stops rotating
Causes
• Expansion due to excessive
heating of the rotor bearings
• Increased rotational friction
Remedy
• Poor conductor of heat(Mo) is
used as anode stem
• Metallic Lubricants such as Silver
& liquid Gallium are used.

13. Cont…
4. Broken stator windings
 No power supply to make the
anode rotate.
Causes
• Heavy radiography exposures
• Excessive heat in the target
material, rotor and its bearings,
• Difference in thermal expansion of
the various components used in the
anode.
Remedy
• Provide safety circuit to terminate
exposure.

14. OTHER FAULTS
A. DEFICIENCIES IN MANUFACTURING
1. Unlike tubes
2. Weed out by test:- Check high voltage stability, cathode
emission, focal spot size, thermal loading and for
rotating anode tubes additional tests such as noise,
vibration, coast time etc. are tested. Not meeting these
specifications are rejected.
3. Hold period:- If tubes are held for 2-4 weeks vacuum
may leak
4. Improper materials:- O2 free Cu bar can cause vacuum
leaks

15. Cont….
B. APPLICATION MISMATCH:- e.g., poor diagnosis and
radiation burns while using standard diagnostic tubes to
produce mammograms
C. IMPROPER DRIVE BY THE POWER SUPPLY:-
1. Filament life is reduced 2-10 times by DC filament than
AC filament.
2. Magnetic materials ( e.g., iron, nickel, cobalt used for
glass-to-metal seal) can be subjected to magnetic
hysteresis, eddy currents etc.)
3. Filament limit:- maximum output current of the filament
is limited

16. CARE OF THE X-RAY
TUBE
1. WARM UP THE ANODE FOLLOWING MANUFACTURER’S
RECOMMENDATIONS
 Performed if the system not been energized for ≥ 2 hrs
 To prevent tube damage from thermal shock
WARM UP PROCEDURES
Make 1st 3-exposures waiting approximately 30s between
each exposures @
75kVp 200mA 1s
Wait 60s, then take 1 exposure @
85kVp 200mA ½ s
Wait 60s, then take the last exposure @
100kVp 200mA ¼ s

17. Cont….
2. MINIMIZE FILAMENT BOOST(“PREP”) TIME
 Current applied for too long will shorten filament life and
will lead to unstable operation.

18. Cont…
3. USE LOWER TUBE CURRENT (mA)
 High tube current will cause evaporation of the tungsten
 Whenever possible, use a lower mA station and a longer
exposure time to arrive at the desired mAs.

19. Cont….
4. FOLLOW RATING CHARTS AND ANODE AND
HOUSING HEATING/COOLING CHARTS
 Operation beyond published ratings will result in
premature focal track wear and tear.
TUBE RATING CHART
o The chart which provides the information about the
details of the electrical loads which may be applied to the
tube without damaging it & the safe duration of such
loads is called tube rating chart.

20. Cont….
o In considering the tube rating three characteristics are
encountered:
 Ability of x-ray tube to withstand a single exposure
 Ability of x-ray tube to function despite rapid exposure
 Ability of x-ray tube to withstand multiple exposure during
several hours of heavy use.
o There are 3 types
A. RADIOGRAPHIC RATING CHARTS
B. ANODE HEATING/COOLING CHART
C. HOUSING HEATING/COOLING CHART

21. RADIOGRAPHIC
RATING CHART
• The safe limit within
which x-ray tubes can be
operated for a single
exposure can be easily
determined by it.
• It is the most imp
because it conveys
which radiographic
techniques are safe or
unsafe for tube
operation.
• Microprocessors are
used to allow only safe
exposures.

22. Rating chart of x-ray room
no.1

23. Rating chart of x-ray room
no.1

24. ANODE
HEATING/COOLING
CHART
• Determines the
maximum heat
capacity of the
anode.
• Determines the
length of time the
tube must be
allowed to cool
before additional
exposures can be
made.

25. HOUSING
HEATING/COOLING
CHART
• Determines the
maximum heat
capacity(1-1.5
million HU) of the
tube housing.
• Complete cooling
after maximum
heat capacity
may take 1-2 hrs.

26. Cont.…
• Thermal rating can be determined by calculating
Energy deposited in the target(E)
=kVp × mA × exposure time in sec
• Unit is heat units(HU)
• SI unit is Joule(J)
1 HU= 0.71 J
1 J= 1.4 HU
• Now the Energy deposited in the target(E)
=kVp × mA × s J

27. CARE OF THE X-RAY
TUBE
5. LIMIT OPERATION TO 80% OF MAXIMUM SINGLE
EXPOSURE RATINGS
 It will minimize the reduction in radiation output
associated with a roughened focal track.
6. DO NOT EXCEED ANODE THERMAL CAPACITY OR
DISSIPATION RATE OF THE TARGET.
7. DO NOT MAKE HIGH mA EXPOSURES ON A COLD
TARGET.
8. AVOID LONG INTERVALS BETWEEN SPOT-FILMS.
o Most common “holdover period”(during which the rotor is
kept at high speed before the rotor brake cycle is
allowed to occur) is approximately 25 s between spot
films

28. Cont.….
9. LIMIT ROTOR START/STOP OPERATIONS
o Minimum of 30-40 s should be between starts
10.DONOT ROTATE THE TUBE HOUSING RAPIDLY
o Tension or pressure will produce to the x-ray tube.
o Gyroscopic effect( resistance to turns in any direction)
may crack or otherwise damage the rotor.

29. Cont.…
11.SOUND COOLING SYSTEM SHOULD BE PROVIDED
o Enormous heat(99%) is generated in the anode during
the exposure.
o Heat can be dissipated one of the 3 ways:-
RADIATION
CONDUCTION
CONVECTION.
o During exposures , heat is primarily dissipated by
radiation whereas between exposures it is primarily
dissipated by conduction.

31.  General life of x-ray tubes is ten of thousands of
exposures.
 And CT tubes are now guaranteed for 50,000 exposures

32. ANY
QUESTIONS???

33. Reference
• Christensen’s PHYSICS OF DIAGNOSTIC
RADIOLOGY(4TH EDITION)
• Stewart Carlyle Bushong’s RADIOLOGIC SCIENCE
FOR TECHNOLOGISTS (10TH EDITION)
• En.m.Wikipedia.org
• www.studentradiographer.com
• www.Radiopaedia.org
• www.spellmahv.com
• www.scribd.com
• www.slideshare.com
• www.sprawls.com