EM RADIATION & EM RADIATION & PHYSICS OF XRAYSPHYSICS OF XRAYS

DR ZOHEIR HUSSEINDR ZOHEIR HUSSEIN

ATOMIC THEORYATOMIC THEORY

Matter is comprised of very small particles Matter is comprised of very small particles known as atoms. known as atoms.

Atoms are can be further subdivided into 3 Atoms are can be further subdivided into 3 basic subatomic particles: basic subatomic particles:

- protons (p+)- protons (p+)

- neutrons (nº) - neutrons (nº)

- electrons (e¯)- electrons (e¯)

Historical OverviewHistorical Overview The Greeks theorized that matter has four basic The Greeks theorized that matter has four basic

components: air, water, earth and fire. components: air, water, earth and fire. Named the smallest division of these components the atom. Named the smallest division of these components the atom.

Theory accepted until early 1800s, when English Theory accepted until early 1800s, when English schoolteacher John Dalton (1766-1844) published his schoolteacher John Dalton (1766-1844) published his work on atomic theory:work on atomic theory: Elements differentiated from one another based on the Elements differentiated from one another based on the

characteristic of masscharacteristic of mass Elements composed of atoms which behaved in an Elements composed of atoms which behaved in an

identical fashion during a chemical reaction.identical fashion during a chemical reaction.

1800s: Russian scientist, Dmitri Mandeleev (1834-1800s: Russian scientist, Dmitri Mandeleev (1834-1907), developed the first periodic table of the elements:1907), developed the first periodic table of the elements: elements are arranged in order of ascending atomic masselements are arranged in order of ascending atomic mass

1911: English physicist Ernest Rutherford (1871-1937) 1911: English physicist Ernest Rutherford (1871-1937) developed a model for the atom which contained a developed a model for the atom which contained a central, small, dense nucleus, which possessed a positive central, small, dense nucleus, which possessed a positive charge and was surrounded by a negative charge. charge and was surrounded by a negative charge.

1913: Niels Bohr (1885-1962), a Denish physicist, 1913: Niels Bohr (1885-1962), a Denish physicist, expanded on Rutherford’s work and proposed a model expanded on Rutherford’s work and proposed a model for the atom which is considered the most representative for the atom which is considered the most representative of the structure of matter.of the structure of matter. Bohr’s atom is likened to a miniatures solar system where Bohr’s atom is likened to a miniatures solar system where

electrons orbit around a central nucleus just as the planets electrons orbit around a central nucleus just as the planets revolve around the sun.revolve around the sun.

Basic Atomic ParticlesBasic Atomic Particles The atom - small, dense centre the The atom - small, dense centre the nucleus, nucleus,

which is surrounded by –vely charged electrons which is surrounded by –vely charged electrons that orbit it at various levels. that orbit it at various levels.

Nucleus – protons (+ve) and neutrons (neutral) Nucleus – protons (+ve) and neutrons (neutral) Protons + neutrons = Atomic mass Protons + neutrons = Atomic mass Electron has a relatively insignificant mass, Electron has a relatively insignificant mass,

1/1,828 that of a proton ( 9.109 x 101/1,828 that of a proton ( 9.109 x 10 -31 -31 kg)kg) Proton – 1.673 x 10Proton – 1.673 x 10-27-27 kg kg Neutron – 1.675 x 10Neutron – 1.675 x 10-27-27 kg kg

When the number of When the number of positively charged protons positively charged protons equals the number of equals the number of negatively charged negatively charged electrons, the atom is electrons, the atom is neutral or stable. neutral or stable.

Because of its electrical Because of its electrical nature, the atom is dynamic nature, the atom is dynamic and ever moving and in a and ever moving and in a constant, vibrating motion constant, vibrating motion because of the strong because of the strong positive nuclear force field positive nuclear force field which is surrounded by the which is surrounded by the negatively charged spinning negatively charged spinning and orbiting electron.and orbiting electron.

Atomic NumberAtomic Number Each elements has its own specific number of nuclear Each elements has its own specific number of nuclear

protons. protons.

This is the key characteristic which distinguishes one This is the key characteristic which distinguishes one element from another. element from another.

The number of nuclear protons in an atom is known as The number of nuclear protons in an atom is known as the the atomic numberatomic number or or zz number. number. The simplest element, hydrogen, possesses only one proton The simplest element, hydrogen, possesses only one proton

and therefore has atomic number of 1. and therefore has atomic number of 1. Helium comes next on periodic table and has two protons, Helium comes next on periodic table and has two protons,

giving it an atomic number of 2. giving it an atomic number of 2. Lead has an atomic number of 82, indicating that within the Lead has an atomic number of 82, indicating that within the

nucleus of an atom of lead there are 82 protons. nucleus of an atom of lead there are 82 protons.

In a neutral atom the number of protons is equal to the number In a neutral atom the number of protons is equal to the number of electrons. of electrons.

-In a stable, neutral atom of hydrogen there is one proton and -In a stable, neutral atom of hydrogen there is one proton and one electron. one electron.

-In a stable atom of lead there are 82 protons and 82 electrons.-In a stable atom of lead there are 82 protons and 82 electrons.

If an atom gains or loses neutrons, the result is an atom called If an atom gains or loses neutrons, the result is an atom called an an isotopeisotope. .

-Isotopes are atoms which have the same number of protons in -Isotopes are atoms which have the same number of protons in the nucleus but differ in the number of neutrons. the nucleus but differ in the number of neutrons.

-Deuterium is an isotope of hydrogen, contains the same -Deuterium is an isotope of hydrogen, contains the same number of protons as hydrogen but also contains one neutron. number of protons as hydrogen but also contains one neutron.

If an atom gains or loses an electron, it is called an If an atom gains or loses an electron, it is called an ionion and the and the atom is said to be ionized. atom is said to be ionized.

Ionization Ionization is the process of adding or is the process of adding or removing an electron from an atom. removing an electron from an atom.

ie when an electron is removed from an atom, ie when an electron is removed from an atom, the atom becomes a positive ion; that is the the atom becomes a positive ion; that is the atom possesses an extra positive charge. atom possesses an extra positive charge.

When an electron is added to an atom, the When an electron is added to an atom, the atom becomes negative ion, ie it possesses an atom becomes negative ion, ie it possesses an extra negative charge extra negative charge

EM RadiationEM Radiation

In terms of modern quantum theory: In terms of modern quantum theory:

EM wave is the flow of photons (also called EM wave is the flow of photons (also called light quanta) through space.light quanta) through space.

Photons are packets of energy that aways Photons are packets of energy that aways move with the universal speed of light move with the universal speed of light (300,000 Km/sec)(300,000 Km/sec)

Electromagnetic radiation (EM) spans a Electromagnetic radiation (EM) spans a continuum of wide ranges of magnitudes of continuum of wide ranges of magnitudes of energy. energy.

This continuum is termed the This continuum is termed the electromagnetic electromagnetic spectrumspectrum. .

The electromagnetic spectrum details all of the The electromagnetic spectrum details all of the various forms of EM radiation.various forms of EM radiation.

One of the common properties of all forms of One of the common properties of all forms of EM radiation is velocity. EM radiation is velocity.

Electromagnetic spectrumElectromagnetic spectrum High energy – GammaHigh energy – Gamma - X- ray- X- ray - Ultraviolet- Ultraviolet - VISIBLE LIGHT- VISIBLE LIGHT - Infrared- Infrared - Microwave- Microwave - Radar- Radar

Low energy - RadioLow energy - Radio

Radiation along the EM spectrum will vary Radiation along the EM spectrum will vary according to the associated frequency and according to the associated frequency and wavelength. wavelength.

Low frequency-long wavelengths are at the Low frequency-long wavelengths are at the bottom of the spectrum with radio waves and bottom of the spectrum with radio waves and microwaves.microwaves.

Visible light is in the centre of the spectrum Visible light is in the centre of the spectrum and at the top of the spectrum are gamma and and at the top of the spectrum are gamma and x-rays having high frequency and short x-rays having high frequency and short wavelengths.wavelengths.

IONIZING RADIATIONIONIZING RADIATION IR arises from both natural and manmade IR arises from both natural and manmade

sources grouped as Particulate and EM sources grouped as Particulate and EM (Photon) radiation(Photon) radiation

Particulate- high energy electrons, protons and Particulate- high energy electrons, protons and neutrons.neutrons.

Produce ionization by direct atomic collisionsProduce ionization by direct atomic collisions Photon radiation- X-rays Gamma raysPhoton radiation- X-rays Gamma rays Produce ionization by other types of Produce ionization by other types of

interactions (photoelectric absorption, interactions (photoelectric absorption, compton scattering)compton scattering)

COSMICOUTER SPACE

TERRESTIALENVIROMENTAL

EXTERNAL

INGESTEDK & C

INHALEDRADON

INTERNAL

NATURAL

NUCLEARREACTORS

W EAPONS

INDUSTRIAL

DIAGNOSTIC THERAPEUTIC

MEDICAL

ARTIFICIAL

SOURCES OF RADIATION

NATURAL SOURCES OF RADIATIONNATURAL SOURCES OF RADIATION

Ionizing radiations in diagnostic Ionizing radiations in diagnostic imagingimaging

X-RAYS:X-RAYS: Conventional RadiographyConventional Radiography FluoroscopyFluoroscopy MammographyMammography CT-scanCT-scan

GAMMA RAYS:GAMMA RAYS: Radioisotope scanningRadioisotope scanning

Properties of Ionization radiationsProperties of Ionization radiations

They have a very short wavelength and so can They have a very short wavelength and so can penetrate materialspenetrate materials

They can cause certain substances to fluoresceThey can cause certain substances to fluoresce

They form an image on a radiographic filmThey form an image on a radiographic film

They produce biological effects which may be They produce biological effects which may be useful as in radiation therapy or harmful as to useful as in radiation therapy or harmful as to cause diseasecause disease

RADIO-SENSITIVITY (RS) OF VARIOUS RADIO-SENSITIVITY (RS) OF VARIOUS HUMAN ORGANSHUMAN ORGANS

High RSHigh RS Medium RSMedium RS Low RSLow RS

Bone MarrowBone Marrow

SpleenSpleen

Lymphatic Lymphatic NodesNodes

GonadsGonads

Eye LensEye Lens

LymphocytesLymphocytes

SkinSkin

Mesoderm Mesoderm Organs (liver, Organs (liver, heart, lungs)heart, lungs)

MuscleMuscle

BonesBones

Nervous systemNervous system

Radio-sensitivityRadio-sensitivity

RS - probability of a cell, tissue or organ of RS - probability of a cell, tissue or organ of suffering an effect per unit of dose.suffering an effect per unit of dose.

Bergonie and Tribondeau (1906): “RS Bergonie and Tribondeau (1906): “RS LAWS”: RS will be greater if the cell:LAWS”: RS will be greater if the cell:

• Is highly mitotic.Is highly mitotic.• Is undifferentiated.Is undifferentiated.• Has a high carcinogenic future. Has a high carcinogenic future.

Biologic effects of ionizing radiationsBiologic effects of ionizing radiations Photons of ionizing radiation absorbed by atoms of water Photons of ionizing radiation absorbed by atoms of water

molecules of the cell- 1˚ ionization.molecules of the cell- 1˚ ionization.

The ejected electron has sufficient energy to cause ionization The ejected electron has sufficient energy to cause ionization of other atoms in the material- 2˚ ionization.of other atoms in the material- 2˚ ionization.

The free formed combine with others to form a new chemicals The free formed combine with others to form a new chemicals in the cell- chemical change.in the cell- chemical change.

This chemical change causes abnormal behavior of the cell- This chemical change causes abnormal behavior of the cell- Biological change.Biological change.

The effects of these changes are stochastic and non-stochastic The effects of these changes are stochastic and non-stochastic effects. effects.

Stochastic effectStochastic effect

Is defined as an effect in which the probability Is defined as an effect in which the probability of occurrence increases with increasing of occurrence increases with increasing absorbed dose, but severity of effect does not absorbed dose, but severity of effect does not depend on the magnitude of the absorbed dose.depend on the magnitude of the absorbed dose.

It is an all-or-none phenomenon, and is It is an all-or-none phenomenon, and is assumed to have no dose threshold so higher assumed to have no dose threshold so higher the dose higher the risk.the dose higher the risk.

3 important consequences of stochastic effect are:3 important consequences of stochastic effect are:

Radiation induced carcinogenesis of which Radiation induced carcinogenesis of which leukemia is the commonest neoplasia.leukemia is the commonest neoplasia.

Congenital malformations from effect during Congenital malformations from effect during organogenesis.organogenesis.

Mutations due to altered biological code on Mutations due to altered biological code on chromosomes in germ cells (sperm & ova) chromosomes in germ cells (sperm & ova)

Non stochastic effectNon stochastic effect Is defined as a somatic effect that increases in Is defined as a somatic effect that increases in

severity with increasing absorbed dose. So severity with increasing absorbed dose. So there is a threshold below which the effect will there is a threshold below which the effect will not occur or will be stochastic.not occur or will be stochastic.

These are usually degenerative effects severe These are usually degenerative effects severe enough to be clinically significant.enough to be clinically significant.

They usually occur in industrial disasters. They usually occur in industrial disasters.

1Sv- Temporary depression of blood count but the 1Sv- Temporary depression of blood count but the victim is likely to recover or may develop stochastic victim is likely to recover or may develop stochastic effect.effect.

5Sv- Death can occur within weeks due to bone marrow 5Sv- Death can occur within weeks due to bone marrow

failure, unless radical medical intervention is effected.failure, unless radical medical intervention is effected.

10Sv- Death occurs within days due to damage of the 10Sv- Death occurs within days due to damage of the GIT lining leading to infections, septicemia or GIT lining leading to infections, septicemia or hemorrhage.hemorrhage.

20Sv- Death within hours due to severe damages to CNS 20Sv- Death within hours due to severe damages to CNS from the cellular debris and not the radiation directly. from the cellular debris and not the radiation directly.

METHODS OF PROTECTIONMETHODS OF PROTECTION

Who should be protected:Who should be protected:

PatientsPatients

StaffStaff

General publicGeneral public Protected against:Protected against:

Primary / useful radiationsPrimary / useful radiations

Stray radiations I.e.Stray radiations I.e. ScatterScatter LeakageLeakage

Parameters available toParameters available to

reduce radiation exposurereduce radiation exposure TimeTime Reduce time of exposureReduce time of exposure Distance Distance By inverse square law By inverse square law Barriers Barriers FiltersFilters Lead shieldsLead shields Concrete wallsConcrete walls

PROTECTION TECHNIQUESPROTECTION TECHNIQUES

Use Posters e.g. Radiation Use Posters e.g. Radiation symbolsymbol

Inverse square law (D Inverse square law (D αα 1/S 1/S22))

Date of LNMPDate of LNMP

Lead sheets/iron sheetsLead sheets/iron sheets

Quality assuranceQuality assurance

Renewable licenseRenewable license

PATIENTSPATIENTS

Use of Aluminum filters close to the tubeUse of Aluminum filters close to the tube Tube shieldingTube shielding Reduce field size with collimationReduce field size with collimation Use fast film/screen combinationUse fast film/screen combination Reduce number of repeatsReduce number of repeats Use highest possible kVp and low mAsUse highest possible kVp and low mAs Use pulsed fluoroscopy rather than continuousUse pulsed fluoroscopy rather than continuous Use lowest possible time of exposureUse lowest possible time of exposure Use adequate protective gearsUse adequate protective gears

STAFFSTAFF Only those required in the room should be presentOnly those required in the room should be present

All should stand behind the barrier during exposureAll should stand behind the barrier during exposure

Must wear adequate protective gear Must wear adequate protective gear

Must be as far as possible from the primary beamMust be as far as possible from the primary beam

Use immobilising devices for restless patientsUse immobilising devices for restless patients

GENERAL PUBLICGENERAL PUBLIC The radiology unit must be reinforced with concrete The radiology unit must be reinforced with concrete

walls and lead shielded doors.walls and lead shielded doors.

The direction of primary beam should not be directed to The direction of primary beam should not be directed to the clinics or waiting areas.the clinics or waiting areas.

Those who are not supposed to be in Radiography suit Those who are not supposed to be in Radiography suit should be kept away.should be kept away.

Should use appropriate protective gear when required. Should use appropriate protective gear when required.

ConclusionConclusion

There are no ionizing radiations There are no ionizing radiations

which are completely safewhich are completely safe

It is of utmost importance to avoid unnecessary It is of utmost importance to avoid unnecessary

ionizing radiations and the radiation exposureionizing radiations and the radiation exposure

should be kept as low as reasonablyshould be kept as low as reasonably

achievable (ALARA) achievable (ALARA)