Week 1 C Chapter 5 Electromagnetic Radiation

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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.

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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.

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Electromagnetic Radiation

• The important properties of the sine-wave model
  are frequency(f) and wavelength(?) 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).

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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.

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Electromagnetic Radiation

• At a given velocity, wavelength and frequency are
  inversely proportional.
• The Wave Formula
• Velocity Frequency x Wavelength

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Electromagnetic Radiation

• With EMF we know the velocity so the formula is
  simplified.
• c f? or f c/? or ? c/f
• As frequency increases, wavelength decreases and
  vice versa
• For electromagnetic radiation, frequency and
  wavelength are inversely proportional.

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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.

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Electromagnetic Spectrum

• Three important ranges.
• Visible light
• Radio frequency
• X-radiation
• Others include
• UV
• IR and microwave

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Electromagnetic Spectrum

• EMF can be measured in three formats
• Energy (eV) used to describe x-rays
• Frequency (Hz)
• Wavelength (m)

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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.

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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.

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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.

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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.

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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

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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Wave model Visible Light

• Light photons not reflected are either absorbed
  or transmitted.
• There are three degrees of absorption
• Transparency
• Translucency
• Opacity

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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.

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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.

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Radiopaque or Radiolucent

• Terms used to describe the appearance of objects
  on the x-ray film.
• Objects that absorb the radiation are called
  radiopaque.

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Radiopaque or Radiolucent

• Structures that attenuate the x-rays are referred
  to as Radiolucent.
• Bone is radiopaque.
• Lung is radiolucent.

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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.

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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.

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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 10-12m.
• X-ray frequency range from 1018 to 1021Hz

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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

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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.

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Plancks Quantum Theory

• X-rays are created at the speed of light or they
  dont exist at all.
• The energy of a photon is directly proportional
  to its frequency.
• A photons energy is inversely proportional to
  the photon wavelength.

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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.
• Plancks quantum physics and Einsteins physics
  of relativity greatly extended these theories.

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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 x-ray imaging.

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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.

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End of Lecture