Wilhelm Conrad Röntgen 1895 X - RAYS JP©

X – RAYS !! ROENTGEN 1895 Induction Coil +ve -ve Cathode Ray Discharge Tube Frau Roentgen’s Hand Wrapped Photographic Plate was EXPOSED X – RAYS !! JP©

Early cold cathode X-ray tube anode 0 V 100 kV Air at low pressure JP©

Thermionic Emission of Electrons X-Ray Tube BASIC PRINCIPLE -ve high voltage +ve Anode +ve Heater current Thermionic Emission of Electrons X-Ray Photons JP©

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 : 10-9 - 10-11 metres JP©

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 JP©

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. 0 2 4 6 8 10 λ x 10-11 m Intensity Maximum electron energy available = eV 50 kV 20 kV λmin JP©

DEPENDS UPON THE TARGET METAL IN THE ANODE FINE [ LINE ] SPECTRUM DEPENDS UPON THE TARGET METAL IN THE ANODE 50 kV 0 2 4 6 8 10 λ x 10-11 m Intensity 20 kV LINE SPECTRA JP©

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 JP©

X-RAY SPECTRUM AS A FUNCTION OF TUBE P.D. Intensity LINE SPECTRA 100 kV 150 kV Voltage / kV JP©

THE ANODE ROTATES AT 3000 RPM ROTATING ANODE X-RAY TUBE rotating anode motor stator tungsten target motor rotor vacuum 100 000V 6.3 V A.C. ball race bearings 0 V hot filament focusing cathode electron beam X-RAYS THE ANODE ROTATES AT 3000 RPM JP©

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. JP©

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 JP©

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 JP©

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 JP©

Lead GRID absorbs scattered X-Rays X-RAY IMAGING Lead aperture Lead cone anode Lead GRID absorbs scattered X-Rays FILM JP©

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 JP©

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. JP©

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. JP©

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. JP©