it includes everything related to interaction with matter of x-ray along with biological effects of radiation

1. INTERACTION OF X-RAY WITH MATTER
AND EFFECTS OF RADIATION
Presented by ;
Niroj Sandha
B.Sc. MIT 1st year
NAMS, BIR HOSPITAL

2. CONTENTS
ATOM
TYPES OF INTERACTION
DIFFERENTIAL ABSORPTION
EXPONENTITAL ATTENUATION
EFFECTS OF RADIATION
SUMMARY
REFERENCES

3. ATOM
Matter is anything that occupies space , is made
up of atom which is composed of nucleon (i.e.
neutron and proton) and electron.
Neutrons are electrically neutral and protons have
positive charge ,both are found in nucleus.
Electrons are negatively charge and circulate
around the nucleus .
The Atomic numer (Z) is the no. of protons in the
nucleus , it is equal to the no. of electrons .
Total no. of protons and neutrons in the nucleus is
known as Mass number(A).

4. ATOMIC STRUCTURE
According to Bohr’s atomic model :
1. Positively charged nucleus surround and revolve by
the negatively charged electrons in a fixed orbits
2. Electron orbit shells are given the codes for
identification K,L,M,N, and so forth from closest to
nucleus to farthest from nucleus .
3. Maximum number of electrons that can exist in each
shell increases with increase in distance from the
nucleus i.e. 2n^2 where ‘n’ is the shell number .

6. Binding energy
It is energy acquired by the electrons due to
strong electrostatic pull of attraction by the
nucleus
Energy required to remove an electron from an
atom is called electron binding energy
It is unique for each shell of each element
It depend on the distance of an electron from
5ye nucleus i.e. inner shell electrons have high
binding energy than outer shell electron

7. Binding energy of tungsten atom

8. Ionization
Removal of one or more electrons form the neutral
atom leaving behind a positive ion .
Electromagnetic radiation with sufficient energy to
eject atomic electron is called ionizing radiation

9. EXICITATION
Electrons of an atom move from inner shell to outer shell
when energy is supplied to neutral atom is called
excitation

10. Beam interaction picture

11. Photon beam interctaction
Attenuation : removal of intensity of the radiation
when it passes through the matter
Absorption:transfer of energy from radiation to the
medium
Scattering :refers to change indirection of photons
Transmission : x ray energy that penetrate through
matter without any of above process

12. DUAL NATURE OF LIGHT
X ray belongs to a group of radiation called
Electromagnetic radiation .
Electromagnetic radiation has dual characteristics i.e. it
comprises both particle and wave
Wave concept
Propagate through space in the form of wave
Waves of all type have wavelength and frequency
C = / . V Where v= frequency , /= wavelength, c=
speed of light

13. Electromagnetic wave ko gif fig
Wave theory of light explains phenomenon like
interference , diffraction, polarization and coherent
scattering

14. Particle concept
When metal surface is irradiated with light , an
electron is ejwcted
Depends on its energy( frequency) not its
intensity
The phenomenon of photoelectric effect and
compton effect is explained on the basis of light
consisting photons or quanta.
Gif of duality

15. Interaction of x ray with matter
x ray interacts with matter through 5 different
mechanism .
They are :
1. Coherent scattering
2. Compton scattering
3. Photoelectric scattering
4. Pair production
5. photodisintegration

16. COHERENT SCATTERING
Incident x ray energy below 10kev interacts with the
target atom causing it to become excited and release
the excess energy as a scattered x ray
Also called classical scattering or Thompson scattering
There are two types of coherent scattering
1. Thomson scattering
2. Rayleigh scattering
Scattered x ray is change in direction and wave length
is equal to that of the incident x ray and therefore equal
energy
No ionization occurs as no transfer of energy of occurs
/no ejection of the electrons .
It is little importance to the diagnostic radiology

17. Figure of coherent scatteing

18. Compton scattering

19. COMPTON SCATTERING
Incident x ray interact with the outer shell electron
target atom , thereby ionizing the atom .
Ejected electron is called Compton electron
Energy of Compton scattered x ray is equal to
difference between the energy of incident x ray and
ejected electron .
This reaction produces an ion pair , a positive atom
and a negative electron known as recoil electron
It contributes around 20% in diagnostic radiography

20. Scatter photon has less energy than the
incident photon .
Wavelength is longer than the incident
photon
Scatter photon undergo additional tissue
interaction

22. Direction of scatter radiation
Scatter radiation travel in a new direction
depending upon deflection angle with the
electron.
It may be as great as 180 degree ( back
scattering )
I. Back scatter can cause artefacts ,such as
cassette strap image .
II. These photons pose major radiation hazard
to the staff ( especially during fluoroscopic
examination )

23. Probabilty of occurrence
Most likely to occur
With outer shell electron and loosely bound electron
As x ray energy increases
Reduce probability of Compton effect
 As atomic number of matter increases
 No effect
 As mass density of matter increase
 More Compton scatter

24. PHOTOELECTRIC EFFECT
• Incident x ray interact with the innershell electron
and is fully absorbed thereby ejecting an electron
from its shell
• the ejected electron escapes with the KE equal to
difference between energy of incident x ray and the
binding energy of the electron.

26. • Earned albert einstein the 1921 nobel prize in physics .
• For low atomic number atom , photoelectron eject
with KE is equal to the energy of incident x ray .
• For high atomic number atom , KE of photoelectron is
proportionately lower in compared to binding energy
of target atom .

27. The photoelectric effect yields
1. photo electron (-ve ion )
2.Positive atom(+ve ion)
3.Characteristic x ray
- •Energy of characteristics x ray are produces when
the void in the k-shell is filled by the subsequent
shell electrons , generally L- shell electrons .
•Energy of characteristics x ray is equal to the
difference of binding energy of both shells
• It acts as secondary radiation and contributes
nothing of diagnostic

28. Characteristic x ray after photelectric

29. Probabilty of occurrence
Incident x ray must have energy equal or
greater than the binding energy of k shell
electron
Inversely proportional to the third power of x
ray energy
Directly proportional to the third power of
the atomic number of an atom.

31. Advantages of photoelectric effect
Contributes around 75% to the medical
imaging .
Does not produce scattered radiation
Enhances natural tissue contrast
I. Since the probability of interaction is proportional
to the third power of atomic number , it
magnifies the difference in tissue composed of
different atomic numbers
II. For example bone and soft tissue

32. Disadvantage of photoelectric
Increase in patient radiation dose , since all
the energy of incident photon is absorbed by
the patient in the photoelectric interaction.

33. Pair production
Production of an electron and positron pair after
complete absorption of the x ray photon.
The energy equivalence of the mass of both
particle is equal of 0.51MeV
That’s why it only Occurs when incident photon
has energy of atleast 1.02MeV
Energy in excess of 1.02MeV is distributed
equally as a kinetic energy
It is unimportant in x ray imaging but is very
much of important in PET imaging in nuclear
imaging

34. Picture of pair production

35. Photodisintegration
X ray of energy greater than 10Mev escapes
interaction with the electron and nuclear
electrostatic field and absorbed directly by
the nucleus
nucleus is raised to excited state and emits
nucleon or nuclear fragments .
It does not occur in diagnostic radiology

36. Picture of photodisintegration

37. DIFFERENTIAL ABSORPTION
• X rays that undergo photoelectric interaction provides
diagnostic information as they do not reach the IR and
produces light areas
• whereas x ray transmitted through the patient without
interaction produces the dark areas of a radiograph
• this difference in absorption of x ray interacrion is called
Differential absorption .
• Both, x rays that are transmitted to the IR and that are
absorbed photoelectrically are equally important
• If all the x rays are transmitted then iimage would be
uniformly black and also if all the x ray photons are
absorbed then it will cause uniformly white . Neither of
cases are appreiciated in diagnostic radiology .

38. • Differential absorption depends on following factors ;
1.Atomic number (Z)
2.Mass density
1. Atomic number
• Probabilty of an x ray undergoing photoelectric is
proportional the third power of At no. of the tissue and
inversely proportional to the third power of x ray energy
• So decrease in compton scattering is not as rapid as
photoelectric with increase in energy .
•
Contd ...

40. 2.Mass density
• Interaction of x ray with tissue is proportional to the
mass demsity of the tissue regardless of type of
interaction .
• Mass denity is quantity of matter per volume.
• We could image bone even if differential absorption
is not (Z) related because bone has higher mass
density than soft tissue .

42. EXPONENTIAL ATTENUATION
When x ray interact with any type of tissue ,
interaction occurs through any 5 mechanism but in
diagnostic radiology only 2 types of interaction are
important .
these interaction depend on atomic no of tissue
atoms , mass density and x ray energy.
The reduction in beam intensity after penetration
through a given thickness of tissue is called
attenuation i.e. they are reduced in number by a
certain percentage of each increment in thickness of
the tissue they go through

43. Deterministic effect of the radiation
The effect which have threshold value below
which the effect doesn’t occur
Once the threshold value has been reach the
severity of an effect increase with radiation
dose
It includes
1. Acute radiation lethality
2. Local tissue damage
3. hematologic depression
4. Cytogenic depression

44. Acute radiation lethality
sequence of events followed by high
radiation exposure leading to death within
days or weeks is called acute radiation
syndrome .
Three lethal syndrome associated with acute
radiation lethality are ;
I. Prodromal period (immediate response )
II. Latent period ( no response )
III. Manifest illness ( haematologic, GI ,CNS syndrome )

45. Table 33-2

46. LD50/60 is the dose of radiation that will result in
death of 50% of irradiated subjects within 60 days
 Table 33-3

47. Mean survival time decreases as the
radiation dose increase

48. Local tissue damage
skin
Depends on the intrinsic radiosensitivity , cell
proliferation and maturation .
Local tissues that are affected immediately
are skin, gonads and bone marrow
Damage to basal cells results in earliest
manifestation of radiation injury to the skin .
The resultant skin damage is seen as
erythema and desquamation

49. Fig of erythema and desquamtion

50. Gonads
Human gonads are critically important target
and responds to doses as low as 100mGyt
Even such low dose can reduce the number of
spermatozoa in male testes and suppress
menstruation in female
Dose of approximately 2Gyt causes temporary
infertility and 5Gyt cause permanent infertility
Moderate such as 250mGy is sufficient to
cause genetic mutation

52. Haemopoietic system
highly radiosensitive system ,consists of bone
marrow ,circulating blood and lymphoid tissue
Derived from pluripotent stem cells which
produce many stem cells like lymphocytes
,granulocytes ,thrombocytes ,erythrocytes.

53. Graph of haemopoeitic system

54. Cytogenetic effects
Cytogenetic is the study of cell ,particularly
cell chromosome .
Radiation induced chromosome aberrations
follow non threshold dose response
relationship
Radiation may damage chromosome by
following
i. chromatid deletion –single hit
ii. Dicentric / ring chromosome – multi hit
iii. Reciprocal translocation –multi hit

57. Ring chromosome are produced if two hits occur on the same
chromosome.
Dicentrics are produced when adjacent chromosome sustain
one hit amd recombine .

58. It results in no loss of genetic material, simoly rearrangement
of genes in incorrect sequence .

59. Stochastic effect
Effects of radiation that may occur by chance
and are result of low dose delivered over a
long period of time
It follows linear ,non-threshold dose response
relationship
The principle stochastic effects are radiation
induced malignancy and genetic effects .

60. Local tissue effects
Chronic irradiation of skin can result in severe
non-malignant changes such as development
of very callaused , discolored ,weathered
apperances in the skin
Even a low dose can produce chromosome
aberration that may not be visible even after
many years of exposure

61. usually the radiation protection guides are
based on the stochastic effects of radiation
and on linear non threshold dose relationship
Consequently the precise dose response
relationship are often not possible to
formulate .
hence, we resort Risk Estimates. They are :
1. Relative risk
2. Excess risk
3. Absolute risk

62. 1. Relative risk
If one observe a large population for stocjastic
radiation effects without having precise
knowledge of radiatiom dose which they are
exposed .
It is computed by comparing the number of
irradiated populations showing stochastic
effect by the number of unexposed population
showing the same stochastic effect
Relative risk =observed case /expected
cases

63. 2. Excess risk
It is difference between observed risk and
expected risk
Observed risk-Expected risk =Excess risk
Leukemia is known to occur in non irradiated
population but if leukemia incidence in
irradiated population exceeds more than
expected then difference betn observed cases
and expected cases would be excess risk .

64. 3. Absolute risk
If at least two dose levels are known , it may
be possible to determine the possible risk
factors
It consist unit of case / population / dose
According to the National committee on
biological effects of Ionizing radiation , this
value is 8*10^2
This is the risk coefficient used by the scientist
to predict stochastic radiation response in
exposed populations

65. Radiation Induced Malignancy
All the radiation induced malignancy follow
linear non threshold dose response
relationship expect the radiation induced skin
cancer
Radiation induced malignancy like leukemia
,cancer increases with the increase in
radiation dose

66. References
Text book of Radiology for Residents and
Technicians
Radiologic science for technologist

67. Thank You