Week 1 C Chapter 5
Electromagnetic Radiation
• A photon is the smallest element of
electromagnetic energy.
• Photons are energy disturbances moving
through space at the speed of light.
• Photons have no mass but they do have
electric and magnetic fields.
Electromagnetic Radiation
• A field is an interaction between different
energies, forces or masses that can not be
seen but can be described mathematically.
• Electromagnetic Radiation can be
represented by the sine-wave model.
• Sine-waves have amplitude.Amplitude is
one half the range from crest to valley over
a sine wave.
Electromagnetic Radiation
• The important properties of the sine-wave
model are frequency(f) and wavelength(λ)
and velocity.
• Frequency is the number of wavelengths
passing a point per second.
• Frequency is identified as oscillations per
second and measured in hertz (Hz).
Electromagnetic Radiation
• Wavelength is the distance from one crest
to another or from any point in the wave to
the next corresponding point.
• The wave parameters are very important.
A change in one affects the value of one or
both of the others.
Electromagnetic Radiation
• At a given velocity, wavelength and
frequency are inversely proportional.
• The Wave Formula
• Velocity= Frequency x Wavelength
Electromagnetic Radiation
• With EMF we know the velocity so the
formula is simplified.
• c= fλ or f= c/λ or λ= c/f
• As frequency increases, wavelength
decreases and vice versa
• For electromagnetic radiation, frequency
and wavelength are inversely proportional.
Electromagnetic Spectrum
• The electromagnetic spectrum includes
the entire range of electromagnetic
radiation.
• The frequency range is from about 102 to
1024 Hz
• Photon wavelengths range from 107 to
10-16m.
• Grouped together, these radiations make
up the electromagnetic spectrum.
Electromagnetic Spectrum
• Three important
ranges.
• Visible light
• Radio frequency
• X-radiation
• Others include:
– UV
– IR and microwave
Electromagnetic Spectrum
• EMF can be
measured in three
formats
• Energy (eV) used to
describe x-rays
• Frequency (Hz)
• Wavelength (m)
Visible Light
• Measured in
wavelength.
• A prism is used to
refract or change the
direction of the
photons.
• Only form of EMF that
we can sense.
Forms of Light
• Visible light ranges from 700nm to 400nm
wavelength.
• Infrared light have longer wavelength
than visible light but shorter than
microwaves.
• Ultraviolet light is located between visible
light and ionizing radiation.
Radiofrequency
• AM radio, FM radio and Television are
other forms of electromagnetic radiation.
• With radio, the frequency is used to
identify the station.
• Short wavelength radiofrequency are
referred to as microwaves.
Ionizing Radiation
• Unlike visible light or radiofrequency,
ionizing electromagnetic radiation is
characterized by the energy contained in
the photon.
• When we use 70 kVp, the photon will have
energy varying from 0 to 70 keV.
Ionizing Radiation
• The frequency is much higher and
wavelength much shorter for x-rays
compared to any other form of
electromagnetic radiation.
• Visible light identified by wavelength
• Radiofrequency identified by frequency
• X-rays identified by energy
Ionizing Radiation
• The only difference between X-rays and
gamma rays is their origin.
• X-rays are produced outside the nucleus.
• Gamma rays are produced inside the
nucleus of radioactive atoms.
Wave-Particle Duality
• A x-radiation photon and a visible light
photon are fundamentally the same except
that x-radiation photons have a much
higher frequency and shorter wavelength.
• These differences change the way they
interact with matter.
• Visible light tends to behave as waves.
Wave-Particle Duality
• X-radiation tends to behave more as
particles than waves.
• Both types of photons exhibit both types of
behavior and this is referred to as the
wave-particle duality of radiation.
• Photons interact with matter when the
matter is approximately the same size as
the photon wavelength.
Wave-Particle Duality
• Radio & television photons wavelength is
measured in meters and interact with long
metal rods called antennae.
• Microwave are measured in centimeters
and react most easily with popcorn &
hotdogs.
Wave-Particle Duality
• Visible light wavelength is measured in
micrometers or nanometers, interacts with
living cells such as the rods and cones in
the eye.
• Ultraviolet light interacts with molecules.
• X-rays interact with atoms and electrons.
• All radiation with wavelengths longer than
x-rays interact primarily as a wave.
Wave model: Visible Light
• Vision is result of specially developed
organ that sense a very narrow portion of
the electromagnetic spectrum.
• When a visible light photon strikes an
object, it sets the molecule of the object
into vibration.
Wave model: Visible Light
• The orbital electrons become excited by
the higher energy. This energy is
immediately irradiated as another photon
of light. This is referred to as reflection.
• Atomic and molecular structure determine
which wavelength of light are reflected.
Wave model: Visible Light
• Light photons not reflected are either
absorbed or transmitted.
• There are three degrees of absorption:
– Transparency
– Translucency
– Opacity
Degrees of Absorption
• If all of the light is
transmitted almost
unaltered, it is
transparent.
• If only some of the
light passes through ,
it is called
translucent.
Degrees of Absorption
• If all of the light is
absorbed, it is called
opaque.
• Attenuation is the
sum of scattering
and and absorption
of radiation.
Radiopaque or Radiolucent
• Terms used to
describe the
appearance of objects
on the x-ray film.
• Objects that absorb
the radiation are
called radiopaque.
Radiopaque or Radiolucent
• Structures that
attenuate the x-rays
are referred to as
Radiolucent.
• Bone is radiopaque.
• Lung is radiolucent.
Inverse Square Law
• Radiation intensity is inversely proportional
to the square of the distance from the
source.
• The reason for the decrease is the
radiation is spread over a wider area.
Inverse Square Law
• The Inverse Square Law is used in
radiography to adjust technical factors for
changes in distance.
• It is also used for radiation protection. The
farther you are away from the source, the
lower the exposure.
Particle Model: Quantum Theory
• Unlike other forms of electromagnetic
radiation, x-ray energy is measured in
electron volts (eV).
• X-ray energies range from 1 to 50 MeV
• X-ray wavelengths range from 10-9 to 1012m.
• X-ray frequency range from 1018 to 1021Hz
Range of X-ray Energies
• Diagnostic Radiography uses the range of
30 kVp to 150 kVp.
• Grenz rays with energies of 10 to 20 kVp
are used in dermatology.
• Therapy uses energies from 200 to 1000
kVp
X-ray Waveform
• X-rays have both
electric and magnetic
fields.
• One wave represents
the electric field and
one the magnetic field
varying at right angles
to each other.
Planck’s Quantum Theory
• X-rays are created at the speed of light or
they don’t exist at all.
• The energy of a photon is directly
proportional to it’s frequency.
• A photon’s energy is inversely proportional
to the photon wavelength.
Matter and Energy
• Like the law of the conservation of matter,
the law of conservation of energy states
that Energy can be neither created or
destroyed.
• Planck’s quantum physics and Einstein’s
physics of relativity greatly extended these
theories.
Matter and Energy
• According to quantum physics and physics
of relativity, matter can be transformed into
energy and vise versa.
• Although matter and energy are
interchangeable, it is energy from the x-ray
photon interacting with tissue and the
image receptor that forms the basis of xray imaging.
Mass Energy Relationship
• Mass and energy are
two forms of the same
medium. This scale
shows the
equivalence of mass
measured in
kilograms to energy
measured in electron
volts.
End of Lecture