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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 = d1

2/d22

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INVERSE SQUARE LAW

I1 = D 22

___ _____

I2 D 12

I1 = Original Intensity

I2 = New Intensity

D 1 = Original Distance

D 2 = New Distance

Examples