Radiology Equipment

1. RADIOLOGICAL EQUIPMENT
Lecture2: X-RAYS
Dr. Emad Taleb

2. • In 1895, Wilhelm Conrad Roentgen,
referred to as father of Diagnostic
Radiology, discovered X-rays accidentally
when experimenting with electrical
discharges in an evacuated tube called a
Crookes' tube.
• In 1901 Roentgen was awarded the very
first Nobel Prize in Physics, X- rays known
also as Roentgen Rays in his honor.
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X-ray: Introduction

3. X-ray: Introduction…
• Invisible rays given off from his
experiment could penetrate a human
hand and project a skeletal image onto
a fluorescent screen.
• Later, he substituted photographic film
to make a permanent record.
• Since then, scientists have discovered
that X-rays are a type of
electromagnetic radiation.
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4. • Longer wavelengths, of wavelength 1–10 nm overlap the range
of extreme ultraviolet band of the electromagnetic spectrum, are
known as Soft X Rays and are less penetrating.
• Shorter wavelengths, about 0.1 nm or less closer to and
overlapping the gamma-ray range, are called Hard X-rays and
are relatively penetrating .
• A mixture of many different wavelengths is known as “white”
X rays, as opposed to “monochromatic” X rays, which
represent only a single wavelength. Frequency of hard X-rays is
higher than that of soft X-rays, and the wavelength is shorter
X-ray in Electromagnetic Spectrum
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5. 5
X-ray in Electromagnetic Spectrum…

6. X-rays: Characteristics
 X-rays have a number of useful physical characteristics that
allow us to utilize them for our benefit.
 can penetrate matter which readily absorb and reflect
visible light.
 This allows us to “see through” things.
 Not all materials are penetrated equally.
 This allows us to see different tissues in an image.
 are absorbed differentially when passing through matter,
the extent of which depends upon the density.
 causes biological alterations (ionization) at the molecular
level.
 causes certain materials to fluoresce (give off light) which
enables us to record an image. 6

7.  When interacting with matter, x-rays follow many of the same
physical principles as light. Such as:
– X-rays act like waves when traveling through space.
– X-rays act like particles when interacting with matter
– X-rays travel in straight lines. Therefore, x-rays cannot go
around corners.
– X-rays diverge from a point source, important for radiographic
image formation
– X-rays obey the inverse square law ,important for radiation
safety..
– X-rays are unaffected by electric and magnetic fields. Therefore,
they cannot be focused or steered.
– X-rays travel at the speed of light.
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X-rays: Characteristics…

8. X-ray: Production
• X-rays are produced by interaction of accelerated electrons with
tungsten nuclei within the tube anode
• Two types of radiation are generated: characteristic radiation
and bremsstrahlung (braking) radiation
• Changing the X-ray machine current or voltage settings alters
the properties of the X-ray beam
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9. • Braking Radiation - electromagnetic radiation produced by the
deceleration of a charged particle when deflected by another charged
particle, typically an electron by an atomic nucleus.
• Thermionic emission is the heat-induced flow of charge carriers from a
surface or over a potential-energy barrier.
• This occurs because the thermal energy given to the carrier overcomes
the binding potential, also known as work function of the metal.
• work function is the minimum energy (usually measured in electron
volts) needed to remove an electron from a solid to a point
immediately outside the solid surface
Braking Radiation
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10. Characteristics X-rays
• A high energy electron interacts with a bound electron in an
atom and ejects it.
• The incident electron is scattered and the target electron gets
displaced from its shell.
• The incident electron energy must exceed the binding energy of
the electron to eject it.
• After the electron has been ejected the atom is left with a vacant
energy level.
• This vacant energy level if it occurs in the inner electron levels
is called a core hole.
• This vacancy is subsequently filled by an electron from a higher
energy level with the emission of a characteristic x-ray photon.
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11. • The characteristic x-ray photon has an energy that corresponds
exactly to the difference in energy between the energy level that
is vacant and the energy level from which an electron falls.
• This is used in various techniques, including X-ray fluorescence
spectroscopy, Energy dispersive X-ray spectroscopy and
Wavelength dispersive X-ray spectroscopy. These are used in
mineral analysis and elsewhere.
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Characteristics X-rays…

12. X-ray Tube and its Components
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13. X-ray Tube
Basic Components of an x-ray tube:
 Air evacuated glass envelope: A vacuum is necessary to
prevent accelerated electrons from colliding with air
molecules.
 Cathode: The cathode is a wire filament (usually tungsten)
that is the source of the electrons
 Anode: The anode is a tungsten disc that acts as the target
for the electrons that come from the cathode. X-rays are
created at the anode.
 Few other components such as cooling mechanisms, the
window of the tube etc. also present
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14.  Xray tube housing
• Made of lead and steel
• To abosrb any stray radiation
• To prevent x-ray photons to leak from
the tube
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X-ray Tube…

15.  Protective Housing(contd.)
• Radiation:
– Absorbs isotropically emitted x-rays
– Leakage: <100 mR/hour at 1 meter (FDA)
– Useful beam emitted through “window”
• Electrical and Heat:
– Special high voltage cable receptables
• Heat: (depends on tube design); MAY HAVE:
– Oil-filled (insulator as well as heat absorber)
– Cooling fans
– Active Heat Exchanger using oil or water
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X-ray Tube…

16.  Internal components Cathode
• The negative side of the tube and has two
primary parts: a filament and focusing cup
• Filament = a coil of wire about 2mm in
diameter and 1 or 2 cm long.
• Dual-filament
• Focusing cup - negatively charged
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X-ray Tube…

17.  Focusing cup
• The filament is embedded in a metal cup that has a negative
charge
• Boiled off e- tend to spread out due to electrostatic repulsion.
The focusing cup confines the e- cloud to a small area
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X-ray Tube…

18.  Tungsten
• Filaments are usually made of tungsten
• Tungsten provides higher thermionic emission(2200o C)
than other metals
• Tungsten has a very high melting point(3370o C)
• Alloy with 1-2% Thorium increases TE efficiency
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X-ray Tube…

19. Anode
 Anode Types
 Stationary:
– Small tungsten target (for x-ray production) embedded in
copper (for heat conduction)
– Limited to low output uses (e.g., dental)
 Rotating Anode:
– Tungsten “ring” provides large total target area
– Rotor: part of induction motor (3400-10,000 rpm)
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20. Collimators
• Sheets of lead placed between X-ray source and the patient
• Restrict dimension of the beam to the FOV in 1D or 2D →
reduce amount of X-rays reaching the patient = only
X-rays inside FOV reach the tissue → dose reduced +
scattered reduced
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21. Anti-scatter Grids
• Parallel or slightly divergent strips of lead foil with aluminium
spacers
• Amount of scattered X-rays absorbed depends on length,
thickness and separation of lead strips
• Some non-scattered X-rays are absorbed → increase in dose to
get same image intensity of one without grid
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22. Detectors and Electronics
• Radiographic x-ray image is detected using light-sensitive
negative film combined with x-ray sensitive screens.
– The film is enclosed in a light-tight cassette in contact with a
screen which absorbs the x-rays with high efficiency
• Computed radiography
– Instrumentation = detector plate (image plate) + separate
reader
• Digital radiography
– Instrumentation = detector and reader are one
unit(Flat panel detectors)
1. Indirect = X-ray converted into light by scintillator →
light converted into electric signal by photon detector
2. Direct = X-ray converted into electric signal by
materials such a:Se. 22

23. The Control Panel
• The three factors that can be varied during producing
radiograph are :
– The kilovoltage (K V) difference applied between the
anode and cathode during exposure.
– The milliamperage (mA) applied to the filament.
– The duration of exposure.
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24. • Higher kv attract the electrons toward the anode by greater
force.
• They smash the anode harder and produce x-ray with higher
energy and greater tissue penetrating power.
• Increasing mA increase the number of electrons cloud around
the filament. Result in higher number of x-ray produced per
second.
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The Control Panel…

25. Block Diagram of The X-ray Machine
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