Principles of Imaging Science I
(RAD119)
Electromagnetic Radiation
Energy
• Definition of energy
–Ability to do work
• Physicist’s definition of work
–Work = force x distance
• Force acting upon object over
distance expends energy
Mechanical Energy
• Action of physical movement
• Two types:
–Potential
–Kinetic
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Chemical Energy
• Energy released from chemical reaction
• Examples:
–Body converts chemical energy from
food into mechanical energy or
movement
–Battery converts chemical energy into
electrical energy
Heat Energy
• Also known as thermal energy
• Results from movement of molecules
• Temperature measures thermal
energy
• Example:
–Toaster converts electrical energy
into heat energy
Electrical Energy
• Electricity
• Results from movement of electrons
in conductor
• Example:
–Light bulb converts electric energy
to light
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Electromagnetic Energy
• Exists independently of objects
• Present ubiquitously and spans an
energy continuum
– Endless ordered arrangement
• Combination of electrical and
magnetic bundles called photons or
quantum
Electromagnetic Energy (EM)
• All types of
electromagnetic
radiation are a
form of energy
• EM energy is the
result of electric
and magnetic
disturbances
traveling through
space
Typically, only the electric wave
is depicted in illustrations
Electromagnetic Energy (EM)
 Pure energy travels through
space at speed of light
 Electric and magnetic waves
90 degrees to each other
 Does not need a medium to
be transmitted unlike
mechanical waves in water
or sound waves in air
 Can travel in a vacuum
 Entire band of energies is
grouped in the EM spectrum
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PHOTONS
• Smallest quantity of any electromagnetic
energy
– Have no mass, no form
• Quantum refers to a small bundle of energy
that travels through space at the speed of
light
– Speed of light = 186,400 miles/sec
= 1.864 x 105 miles/sec
= 3 x 108 m/sec
–Velocity of all electromagnetic radiation
PHOTON PROPERTIES
Electric & magnetic fields
that continuously change
in a wavelike motion
Field: Interaction among
the electric and magnetic
energies
Sine Wave: Variation of the
interactions is represented
as a sine wave
SINE WAVE DEFINITION & TERMS
 Disturbance in a medium
• Amplitude
– One half the range of
the wave that varies
from crest to valley
– Height of the wave
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Sine Wave Terms
• Wavelength
– Distance
between adjacent
crests or valleys
– Measured in
metric meters
– Represented by
lambda (λ)
SINE WAVE TERMS
• Frequency
– # of wavelengths
that pass a given
point per second
– Cycles/sec
– Oscillations/sec
– Measured in Hertz
(Hz)
1 Cycle/second = 1 Hz
Wavelength & Frequency Relationship
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SINE WAVE TERMS
• Period: Time to complete
one cycle of a wave
– TIME /#CYCLES
– Wave with a
frequency of one cycle
per second
= 1.0 sec period
– Wave with a
frequency of two
cycles per second
= 0.5 sec period
Two Sine Wave Comparison
1 sec/2cps =
0.5 Period
1 sec/4cps =
0.25 Period
WAVE EQUATION
• Relationship between the sine wave parameters
– Change in one parameter affects the value of one or
both parameters
– Amplitude is not related to frequency or wavelength
• Equation
– Velocity = Frequency x Wavelength
• As velocity decreases, frequency decreases to
maintain wavelength
• As velocity is maintained, frequency and
wavelength are inversely proportional
– frequency = Velocity/Wavelength
– Wavelength = Velocity/frequency
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PARTICLE MODEL
• Applied to electromagnetic radiation
• Planck’s Quantum Theory
– Direct relationship between photon energy and
frequency
• E = hf
– E = Photon Energy
– h = Planck’s constant 4.15 X 10 -15 eVs
– f = Frequency Velocity (c) = frequency x wavelength
EM SPECTRUM
• Continuum of electromagnetic energies
• The full range of all of the different types of
electromagnetic radiations arranged in order of
increasing energy:
– Radio
– Radar/microwaves
– Infrared
– Visible light
– Ultraviolet
– X-rays and gamma rays
• Represents frequency, wavelength, and energy
EM SPECTRUM
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EM SPECTRUM
EM SPECTRUM
• Wavelength and frequency are inversely
proportional.
• Wavelength and energy are inversely
proportional.
• Energy and frequency are directly proportional.
Electromagnetic Interactions
• EM interaction with matter is based upon
wavelength
– EM energy interacts with objects that have
a size similar to the wavelength
• Radio/TV (km) – antennae
• Microwaves (cm) – food
• X-ray, Gamma ray – atoms
–Visible light acts more like a wave
when it interacts with matter
»Has particle properties
–X-rays behave more like particles due
to ionizing potential
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Light Characteristics
 Wave and particle
characteristics
 Visible light refers to the
light we can see (wave)
 Infrared light, ultraviolet
light
 Warmth and sunburn are
the manifestations of UV
energy (particles)
 The intensity of light is
related to how many
particles are emitted from
the source and distance
Light Characteristics
• Transmission
– Passing of light rays
through a substance
• Air, clear glass, or the
near vacuum of space
Wave Model
• Light photons are
transmitted,
attenuated, or
absorbed
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Wave Model
• X-ray photons that interact with the
body are attenuated or absorbed
RADIOGRAPHIC TERMINOLOGY
• Radiopaque
– Anatomical structures that absorb x-ray
photons
– Demonstrate anatomical structures white in
the image
– Bones
• Radiolucent
– Anatomical structures that partially absorb or
attenuate x-ray photons
– Demonstrate structures grey in the image
– Soft tissue, organs, muscle
Radiographic Terminology
• Density (Brightness)
– Degree of blackening
in the image
– High Density (Dark)
– Low Density (White)
• Contrast (Grey Scale)
– Long Scale Contrast
• Many shades of
grey
• Low contrast
• CXR, Abdomen
• Short Scale Contrast
• Black and white
• High contrast
• Bony anatomy
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Radiopaque or Radiolucent?
Density
Long Scale vs Short Scale Contrast
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Scale of Contrast
Contrast
INVERSE SQUARE LAW
• Demonstrates the similarity of
x-rays and light rays
• The intensity of radiation
decreases with the square of
the distance from the source
– Doubling the distance from
the source decreases the
intensity 4x.
– Halving the distance from the
source increases the intensity
4x.
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Inverse Square Law
• Light also acts like particles
• Even though these photons are
steadily emitted by the light
source, as you move farther away
from the source, fewer photons
reach you
• They spread out as they travel in a
wider area away from the source
THE INVERSE SQUARE LAW
THE INVERSE SQUARE LAW
• The intensity of the radiation decreases with
an increase of distance from the source (and
vice versa)
• Intensity is inversely proportional to the
square of the distance
• Formula: I2 = I1 (d1/d2)2
• I1 = Old intensity I2 = New intensity
• d1 = Old distance d2 = New distance
• Formula may also be expressed as:
I1/I2 = d12/d22
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INVERSE SQUARE LAW
I1
___
=
D 22
_____
D 12
I2
I1 = Original Intensity
I2 = New Intensity
D 1 = Original Distance
D 2 = New Distance
Examples
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