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 10-

12m.

• 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 x-ray 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