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15 Νοε 2013 (πριν από 4 χρόνια και 5 μήνες)

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Principles of Imaging Science I

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
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 10
5
miles/sec

= 3 x 10
8

m/sec

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
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

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:

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

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

Anatomical structures that absorb x
-
ray
photons

Demonstrate anatomical structures white in
the image

Bones

Anatomical structures that partially absorb or
attenuate x
-
ray photons

Demonstrate structures grey in the image

Soft tissue, organs, muscle

Density (Brightness)

Degree of blackening
in the image

High Density (Dark)

Low Density (White)

Contrast (Grey Scale)

Long Scale Contrast

grey

Low contrast

CXR, Abdomen

Short Scale Contrast

Black and white

High contrast

Bony anatomy

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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

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
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: I
2

= I
1

(d
1
/d
2
)
2

I
1

= Old intensity I
2

= New intensity

d
1

= Old distance d
2

= New distance

Formula may also be expressed as:
I
1
/I
2

= d
1
2
/d
2
2

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INVERSE SQUARE LAW

I
1 =
D

2
2

___ _____

I
2
D

1
2

I
1 = Original Intensity

I
2 = New Intensity

D

1

= Original Distance

D

2

= New Distance

Examples