Radiology Third Year

2. Wilhelm Conrad Röentgen
• Professor of Experimental
Physics
– Würzburg University
• Discovered x-rays
– 8 November, 1895
• Awarded first Nobel
Prize for Physics
– 1901

3. History of x-ray:
• Roentgen placed his wife’s
hands on photographic
plate and exposed it to
unknown radiation for 15
minutes.
• When he developed the
photographic plate, the
outline of bones of her
hand could be seen.
• He named it x-ray.

4. Nature of the atom:
• Simple substances are called elements. There are 105
elements.
• The atom is the smallest particle of an element that has
the characteristic properties of that element.
• It consists of nucleus surrounded by orbital electrons.
• The nucleus is composed of protons and neutrons and
they are called nucleons.

5. • XAtomic number (Z): is the number of
protons inside the nucleus that equal
the no. of electrons . It determine the
chemical properties of atom & identify
the identity of element.
• XMass number (A): the total number of
protons & neutrons (nucleons).
A
• Nuclide is defined as zX

6. • Electrostatic force is a
force between positively
charges nucleus and
negatively charged
electrons (attracting
force) balances the
centrifugal force of
rapidly moving electrons .
• That keeps electrons
maintained in their shells.

7. • Electron Binding
energy (Ionization
energy):
• It is the energy
required to remove
electron from a given
shell.
• It should exceeds the
eletrostatic force
binding that electron to
nucleus.

8. Atom (cont.)
• The inner shells have more binding energy
more than outer shells.
• E.g. K-shell > L-shell> M-shell ..etc.

9. Ionization:
• Atom is ordinary neutral as the
number of electrons equal the number
of protons.
• If atom loses an electron, it becomes a
positive ion and free electron is a
negative ion.
• This process of forming an ion pair is
termed Ionization.

10. Ionization (cont.)
• XIonization of inner shell electrons
(K, L) require high energy to be
ejected from their orbit (X-ray,
Gamma rays or high energy particles)
.
• Ionization of electrons on outer shells
require low energy particles (ultraviolet)

12. Nature of radiation:
• X1- Corpuscular or particulate
radiation:
• A minute particles which have mass &
charge traveling at straight line with high
speeds.
• A- Alpha Particles: composed of Helium
nuclei (2P+2N) without orbital electrons.
• Because of their double charge & heavy
mass they loss their energy very quickly
and have shallow tissue penetration .

13. Nature of radiation (cont.)
• B- β- Particles:
• They are emitted from nuclei of radioactive
atoms & possess 1 unit of negative charge.
• They are more penetrating than α-particles.
• C- Cathode Rays (electrons):
• Streams of electrons passing from the hot
filament of cathode to anode target in x-ray
tube.

14. Nature of radiation (cont.)
• The capacity of particulate radiation to
ionize atoms depends on its ;
• Mass, velocity and charge.
• The rate of loss of energy from a
particle as it moves along its track
through matter (tissue) is called Linear
Energy Transfer (LET).
• The slower heavy particles have higher
LET.

15. Nature of radiation (cont.)
• 2- Electromagnetic radiation:
• It is a propagation of energy through space
accompanied by electric and magnetic force field
where they are perpendicular to each other. e.g. Xray & Gamma rays.
• Electromagnetic radiations are arranged according
to their energies in what is termed electromagnetic
spectrum.

16. Nature of radiation (cont.)
• Electromagnetic spectrum (EMS):
• Energies in EMS are grouped according their
wavelengths or energy of their photons .
• They ranges from radio-waves to gamma & xrays.

17. Nature of radiation (cont.)
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EM radiation regard as both a particle & wave.
Particle concept:
Discrete bundle of energy → Photons
( Quanta).
Photons have no mass or weight travel in straight line & carrying EM
energy.
Wave concept:
EM radiation → Waves characterized by;
1- Velocity →speed of wave (speed of light 3×108 m/s).
2- Wavelength (λ) → distance between the crest of one wave & the
crest of the next.
3- frequency (F): refers to the number of wavelengths that pass a
given point in a certain amount of time.
C= λ√ (lambda × nu)
C= velocity of light, λ= wavelength in meters, √= frequency in hertz
(cycle per second).

18. Waves
Short Wavelength
Long wavelength
•
•
•
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wavelength
All light waves travel at the same speed, c = 300,000 km/s
Wavelength is the distance between two crests of the wave
Frequency is the number of crests that pass by you in a
second
The longer the wavelength, the lower the frequency, the lower
the energy of the photon

19. What are x-rays?
• XA weightless bundles of energy
(photons) without an electrical charge that
travel in waves with a specific frequency at
the speed of light. X-ray photons interact
with the materials they penetrate and
cause ionization.

20. Properties of x-ray
X1- x-ray are invisible and weightless.
2- They travel in straight line.
3- They travel at the speed of light.
4- They have a wide range of wavelengths.
5- They can not be focused to a point; over
distance the beam diverges like beam of
light.

21. Properties of x-ray (cont.)
6- due to their short wavelengths , they penetrate
materials that absorb or reflect visible light.
7- They are absorbed by matter; that depends on
atomic structure of matter and wave-length of xray.
8- They cause certain substances to fluoresce ; to
emit radiation of long wavelength (visible or
ultraviolet rays).
9- they produce biologic changes in living cells.
10- they can ionize gases and materials they
penetrate.

22. Interaction of x-ray with a matter:
• When x-ray photons
arrive at the patient , one
of several events may
occur;
• 1- x-ray can pass through
the patient without any
interaction.
• 2- x-ray photons can be
completely absorbed by
the patient.
• 3- x-ray photons can be
scatered.

23. Interaction of x-ray with a matter(cont.):
• At the atomic level 4 interactions could be
occur when x-ray photons interact with
matter;
• 1- No interaction.
• 2- Absorption or photoelectric effect.
• 3- Compton scatter.
• 4- Coherent scatter.

24. 1- No interaction:
• The x-ray photon
passes through the
atom unchanged and
leaves the atom
unchanged.
• It is responsible for
producing densities on
film and make dental
radiography possible.

25. 2- Absorption & Photoelectric effect:
• Absorption:
• X-ray photon may be completely
absorbed by tissue.
• At atomic level absorption occurs
as a result of the photoelectric
effect.
• An x-ray photon collides with a
tightly bound, inner shell electron
and give up all of its energy to
eject the electron from its orbit.
• The ejected electron is termed a
photoelectron and has a negative
charge and absorbed by another
atom.
• The photoelectric effect accounts
for 30% of dental x-ray.

26. 3- compton scatter
• X-ray photon may be deflected
from its path as it termed
scatter.
• In compton scatter , x-ray
photon collides with loosely
bound, outer shell electron and
gives up part of its energy to
eject it .
• The ejected electron is termed a
compton or recoil electron with
negative charge.
• Compton scatter accounts for
62% of the scatter in diagnostic
radiology.

27. 4- coherent scatter:
• A coherent or unmodified
scatter occurs when a low
energy x-ray photon interacts
with outer shell electron.
• No change or no ionization
occurs.
• The x-ray photon is scattered in
different direction than the
incident photon.
• The x-ray photon is unmodified
and simply change its direction
without change in energy.