1. Wilhelm Conrad Röntgen
1895
X - RAYS
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2. X – RAYS !! ROENTGEN 1895 Induction Coil +ve -ve
Cathode Ray Discharge Tube
Frau Roentgen’s Hand
Wrapped Photographic Plate
was EXPOSED
X – RAYS !!
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3. Early cold cathode X-ray tube
anode
0 V
100 kV
Air at low pressure
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4. Thermionic Emission of Electrons
X-Ray Tube
BASIC PRINCIPLE
-ve high voltage +ve
Anode +ve
Heater current
Thermionic Emission of Electrons
X-Ray Photons
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5. Wavelength range : 10-9 - 10-11 metres
On Average 99% of each electron’s energy is converted into heat energy.
X-RAYS ARE PRODUCED IN TWO WAYS.
1. A BACKGROUND BREMSSTRAHLUNG SPECTRUM
2. A FINE LINE SPECTRUM
Wavelength range : metres
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6. BREMSSTRAHLUNG RADIATION SPECTRUM
ACCELERATING CHARGES RADIATE ELECTROMAGNETIC RADIATION
When a fast-moving electron swings around a heavily charged nucleus, its acceleration changes rapidly. +
NUCLEUS
BREMSSTRAHLUNG radiation
Photon Energy, E = hf
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7. BREMSSTRAHLUNG BACKGROUND SPECTRUM
Many X-Ray wavelengths [ down to a certain minimum ] may be produced by a particular X-Ray tube, depending upon how much of the electron’s energy is converted in this way.
λ x m
Intensity
Maximum electron energy available = eV
50 kV
20 kV
λmin
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8. DEPENDS UPON THE TARGET METAL IN THE ANODE
FINE [ LINE ] SPECTRUM
DEPENDS UPON THE TARGET METAL IN THE ANODE
50 kV
λ x m
Intensity
20 kV
LINE SPECTRA
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9. LINE SPECTRUM
Produced after an electron knocks out an inner electron from one of the target atoms
Electrons from a higher energy level can then fall in to a vacant energy level.
Excess energy is lost as an X-Ray photon
NUCLEUS K L M e e e e
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10. X-RAY SPECTRUM AS A FUNCTION OF TUBE P.D.
Intensity
LINE SPECTRA
100 kV
150 kV
Voltage / kV
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11. THE ANODE ROTATES AT 3000 RPM
ROTATING ANODE X-RAY TUBE
rotating anode
motor stator
tungsten target
motor rotor
vacuum V
6.3 V A.C.
ball race bearings
0 V
hot filament
focusing cathode
electron beam
X-RAYS
THE ANODE ROTATES AT RPM
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12. ROTATING ANODE X-RAY TUBE
THE TUBE IS IMMERSED IN OIL TO ASSIST COOLING.
THE ANODE IS ROTATED SO THAT IT DOES NOT MELT.
X-Ray QUALITY [= penetrating power] is increased by increasing the p.d. across the tube.
X-Ray INTENSITY [ number of photons per second] is increased by increasing the filament current.
This is the way in which the exposure time to produce a photographic plate is controlled.
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13. ATTENUATION OF X-RAYS
IN A VACUUM, OR AIR, ATTENUATION OBEYS THE INVERSE SQUARE LAW
IN A MATERIAL OF THICKNESS X metres
Where I = the transmitted intensity in Wm-2 , I0 = the incident intensity and
μ = the linear attenuation coefficient.
% transmission
100 50 x
the half thickness
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14. The mass attenuation coefficient, μm, is the attenuation x
the half thickness is the thickness of material that halves the X-Ray intensity
The mass attenuation coefficient, μm, is the attenuation
per unit mass of material. 
where ρ is the density of the material
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15. X-RAY IMAGING X-rays cannot be focused. They only make shadow images.
We therefore need to produce a point source.
The geometry of the anode restricts the angular beam width to about 17o.
The width of the beam is further limited with strips of lead.
anode
Lead aperture
Lead cone
Narrow X-Ray Beam
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16. Lead GRID absorbs scattered X-Rays
X-RAY IMAGING
Lead aperture
Lead cone
anode
Lead GRID absorbs scattered X-Rays
FILM
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17. evacuated glass envelope
IMAGE INTENSIFIER TUBE
photocathode
anodes
fluorescent screen B
fluorescent screen A
electrons
X RAYS
to TV camera
evacuated glass envelope
Screen A converts X – Rays into light
Light releases photoelectrons from the photocathode
Electrons accelerated by anodes
The energy gained by the electrons increases the intensity produces in screen B by a factor of 100
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18. Contrast Media
Barium sulphate is used for X-rays of the digestive system. It is given as a white liquid drink (barium meal) or into the back passage (barium enema). X-rays cannot go through it, so when the X-ray pictures are taken, the outline of the stomach or bowel shows up on the X-ray.
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19. CT SCANNER
X – Ray source moves around the circular tube sending X - Rays through the patient in a fan shaped beam.
X –Ray detector moves around in time with the source and measures the X – Ray strength in each position.
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20. Computed Tomography Imaging (CT Scan, CAT Scan)
Each time the x-ray tube and detector make a 360 degree rotation and the x-ray passes through the patient's body, the image of a thin section is acquired.
During each rotation, the detector records about 1,000 images (profiles) of the expanded x-ray beam.
Each profile is then reconstructed by a computer into a two-dimensional image of the section that was scanned.
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