Final Flashcards
1
Q
Substance
A
any substance with a definite constant composition. (thin sulfur diamond) always composed of the same thing
2
Q
Element
A
simple substance, can’t be decomposed into simpler substances by ordinary means.
3
Q
Atom
A
smallest subdivision of an element.
4
Q
Physics
A
science that deals with occurrences in nature embracing mechanics, heat, light, sound, electricity and magnetism. Study of non-living things.
5
Q
Matter
A
Matter - Anything that has shape, occupies takes up space and weight.
6
Q
Mixture
A
two or more substance combined.
7
Q
Atom
A
smallest subdivision of an element.
8
Q
Compound
A
complex substances chemical union of 2 or more elements in definite composition.
9
Q
Molecule
A
smallest subdivision of a compound having the physical properties of the compound.
10
Q
the degree of attraction is what determines the state (how tightly packed molecules)
A
- Tight bonds = solid
- Loose bonds = liquid
- Loosest bond = gas
11
Q
Energy
A
is the actual or potential ability to do work. Unit for energy JOULE
12
Q
5 forms of energy
A
5 forms of energy
- Mechanical = Two forms
a. Kinetic – motion
b. Potential – stored - Heat
- Chemical – Ex: batteries
- Electrical
- Nuclear – Ex: comes from nucleus
- Electromagnetic (disturbances in space)
13
Q
Energy and Matter are..
A
are interchangeable! - E=MC^2
14
Q
Law of Conservation of Energy:
A
Law of Conservation of Energy:
• Energy can neither be created or destroyed.
• Total amount of energy in the universe is constant.
• Energy will flow from a higher to a lower level in absence of outside work.
15
Q
Components of the Atom:
A
Components of the Atom:
• Nucleus – contains the atom’s mass, composed of
protons and neutrons.
• Protons – are positively charged particles.
• Neutrons – a neutral charge in the atom.
• Orbits - shell
• Electrons – negatively charged particles.
• Atomic Mass – the amount of protons & neutrons.
• Atomic Number - # of protons.
16
Q
Electron binding energy
A
is the amount of energy that is required to completely remove an electron from an atom or a molecule. The incoming electron needs to have equal or more energy to the electron binding energy to eject it from its orbit
17
Q
Isotope
A
Unstable atom. Has the same atomic number (# protons) but different atomic weight (# neutrons)
A stable atom: must contain 8 electrons in the outermost shell.
18
Q
Ionization
A
ADDITION or REMOVAL of an electron from an ATOM resulting in the formation of an ION PAIR.
19
Q
Valence number
A
of electrons in the outermost shell of the atom.
20
Q
Methods of Ionization
A
- X-Ray bombardment of matter – x-ray photon
enters an atom and removes an electron from one of
its shells resulting in the formation of an ion pair. - Thermionic emission – boiling off electrons in the
filament. - Electron stream bombardment
- Spontaneous breakdown of radioactive materials
- Light ray bombardment of certain materials
- Chemical ionization
21
Q
frequency and wavelength are…
A
inversely proportional.
22
Q
Intensifying Screens
A
convert x-ray photon energy into visible light energy to
intensify the film.
-The amount of light is based on the size of
phosphors crystals and the thickness of the layer.
23
Q
Excitation
A
the TRANSFERRING of ENERGY to an ATOM. In the excitation process an electron is moved to a higher energy level within the atom, has too much energy in its shell that needs to be released.
24
Q
Electromagnetic Spectrum:
A
details all of the various forms of EM radiation. The velocity of EM energy is equal to the speed of light.
• Long Waves – low energy
• Short Waves – high energy
25
Wavelength for diagnostic x-ray
0.1 - 0.5
26
Velocity
equals the speed of light
27
Frequency
the number of waves that pass a particular point in a certain time frame.
28
Properties of X-Ray
Properties of X-Ray
1. Highly penetrating invisible rays.
2. Electrically neutral. - No charge.
3. Polyenergetic and heterogeneous.
4. Releases very small amounts of heat. - dangerous
to biological tissue
5. Travel in straight lines.
6. Travel at the speed of light, 3 x 10^8 meters per
second in a vacuum.
7. Can ionize matter.
8. Cause fluorescence of certain crystals.
9. Cannot be focused by a lens.
10. Affect photographic film.
11. Produce chemical and biological changes in
matter through ionization and excitation.
12. Produce secondary and scatter radiation. - prove
by leaving the cassette in the room.
29
Atomic Nature
* Atoms contain the positive charge of the protons and the negative charge of the electrons.
* Protons are locked within the nucleus by very strong forces.
* Electrons are outside of nucleus, bound by relatively weak forces.
30
Electrostatics
• The study of the distribution of fixed charges, or
electrons at rest
Law of Electrostatics: (5)
1. Repulsion-Attraction Law
Like charges repel
Opposite charges attract
31
Electrostatics
•The study of the distribution of fixed charges, or electrons at rest
32
Law of Electrostatics: (5)
1.Repulsion-Attraction Law
Like charges repel
Opposite charges attract
33
2. Inverse Square Law
The force between 2 charges is directly proportional to their magnitudes and inversely proportional to the square of the distance between them.
If it's closer= stronger. Father= weaker
I1/I2=D2/D1
34
3. Distribution Law
Electrical charges reside only on the external surface of the conductor.
35
4. Concentration Law
Concentration of charges are greater on the curved surface where the curvature is the greatest.
36
5. Movement Law
Only negative charges move along solid conductors.
37
Electrification
process of electron charges being added to or subtracted from an object.
38
Friction
removal of electrons from one object by rubbing it against another of a different kind.
39
Contact
occurs when 2 objects come in contact so that charges can move from one object to the other
so the charges are distributed evenly between the objects.
40
*If an electroscope is subjected to an intense beam of ionizing x-ray photons, the air becomes ionized.
Which then the ionized atoms draw electrons from the leaves causing the reduction of charges on the leaves making the leaves relax and move closer together. *
41
3. Induction
method used to charge an object without actually touching the object to any other charged
object.
42
Electric field
field extending outward in all directions from a charged particle, such as a proton or an electron.
43
Electrodynamics-
• Electrons that are moving predominately in the same direction are often referred to as electric current.
44
Electric Current
a flow of electrons through a conductor, the size of the current is proportional to the rate of electron flow. Measured in coulomb per second or ampere.
45
Conductor
something that allows electricity to flow through it easily. Gold is most effective conductor but most expensive, that is why copper is most used (less $)
Ex. Water and metals
46
Insulator
something that does not allow electricity to flow through it easily.
Ex. Glass, special rubbers, wood, plastic
47
Semiconductor
material whose electrical resistance can be switched between insulating and conducting. "allow flow in one direction only"
Ex. Silicon - most commonly used
48
Superconductor
substance whose electrical resistance essentially disappears at temperatures near absolute zero.
Ex. titanium, MRI machine.
49
Factors of an electric circuit
1. ampere
2. volts
3. resistance
50
Current Flow
•The direction of travel of the electrons is defined as either direct current (DC) or alternating current (AC)
51
•Direct Current
Electric current in which electrons are flowing in one direction only.
52
•Alternating Current
Electric current first moves in one direction and then reverses and moves in the opposite direction.
53
Current (amps, # of electrons)
* The quantity, or number, of electrons flowing is sometimes referred to as the current.
* The unit of current is Ampere, sometimes called the amp for short, and it is represented by the symbol (A).
* 1 ampere = 1 coloumb of electrical charge flowing per second
* In x-ray we use millamps because if we use amps, this would electrocute the patient
1 ampere-1000
54
Resistance
•The amount of opposition to the current in the circuit
is called resistance.
•The unit of resistance is measured in/called ohm, it is
represented by the symbol Ω (omega).
•Ability of any current to flow
55
resistance will be present in any circuit no matter what but, it will depend on:
1. Type of conductor
2. length
3. diameter/ cross-section
4. Cooler temperatures
What we want is short length, big diameter, cooler temperatures
R=V/I
56
Volts, EMF, Potential Difference
•Is the force or strength of electron flow.
•Emf (electromotive force): is actually the total
maximum difference of potential between the positive
and negative ends of the electron source.
•emf = potential difference.
•Measured in volts (V). volt = joule per coulomb
57
Ohm's Law
•Describes the relationship that exists between voltage, resistance, and current. Ohm's Law states that the amount of current flowing in a circuit is equal to the applied voltage divided by the circuit resistance.
V=IR
58
Power= Watts
•Power is measured in a circuit in Watts
•Watts is amount of energy produced in a given amount
of time and this is why its stated as kilowatts per hour
•We don’t deal with watts in x-ray
P = IV
59
•Series Circuit
An electric circuit designed to send electrons through various resistance devices by linking them one after the other.
•To calculate the equivalent resistance of a Series Circuit you add up all the resistors.
Rt = R1 + R2 + R3
60
Parallel Circuits
An electric circuit designed to send electrons through various resistance devices by giving each component its own branch.
•To calculate the equivalent resistance of the circuit you add the reciprocals of the resistors and then flip it back over.
61
MAGNETISM:
| Definition
Definition: fundamental force exerted by magnets when they attract or repel each other caused by the motion of charged particles (electrons)
62
MAGNETIC FIELD:
* Created when a charged particle (electron) is in motion
| * The magnetic force field created perpendicular to the motion of the particle
63
SPIN MAGNETIC MOMENT:
•Spinning of a single electron on its axis
•Electrons behave as if they rotate on an axis
clockwise or counter-clockwise.
64
ORBITAL MAGNETIC MOMENT:
•The magnetic field induced by the spinning electron
•The magnetic force field perpendicular to the motion
of the particle (electron)
•When negatively charged electrons orbit the nucleus
of an atom
65
MAGNETIC DIPOLES:
•The small magnet created by the single electron orbit around its nucleus
66
MAGNETIC DOMAIN:
* Accumulation of many atomic magnets with their dipoles aligned
* Group of atoms that have a net magnetic field
67
MAGNET:
•When all magnetic domains in an object are aligned
• An object that exhibits a uniformly strong magnetic
field
68
LINES OF FORCE:
LINES OF FORCE:
•Known also as "lines of flux", "magnetic field"
•Force fields that are created when magnetic dipoles
orient to create a magnet
•Lines flow not only through the magnet itself but
outside the magnetic material, forming a three-
dimensional field surrounding the magnet
•Imaginary lines around the magnets, we cannot see it
69
FLUX DENSITY:
•The stronger the magnetic field, the greater the number of lines of flux therefore the greater flux density
70
THE TWO PRIMARY UNITS USED TO MEASURE THE STRENGTH OF A MAGNETIC FIELD
1. Weber (Wb)
| 2. Gauss
71
THERE ARE 3 PRINCIPAL TYPES OF MAGNETS:
1. NATURAL MAGNETS:
•Earth is the largest natural magnet
•Weakest natural magnet
•Are created when iron oxide (magnetite) remains in
the earth's magnetic field for ages, slowly orienting
the magnetic dipoles are same direction.
2. ARTIFICIAL PERMANENT MAGNETS:
•Manufactured from a steel alloy called alnico,
composed of aluminum, nickel, and cobalt, or iron.
•While, its hot alnico/ or can be iron, is subjected to the
field of a strong commercial magnet to permit easier
orientation of the magnetic dipoles. Upon cooling, the
magnetic field becomes relatively permanent.
•If the material is re-heated or hit with extreme force,
the magnetic property can be destroyed, because the
domains may be jarred from their alignment.
3. ELECTROMAGNETS:
• Temporary magnets produced by moving electric
current. Without electricity, there would not be a
magnetic field.
72
LAWS GOVERNING MAGNETISM: (3)
LAWS GOVERNING MAGNETISM: (3)
1.Repulsion-attraction: like poles repel; unlike poles attract. Lines of force act the same way.
2. The inverse square law: The force between two magnetic fields is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance between them. (an object gets further away, the influencing field decreases because of the increased area it effects).
3. Magnetic Poles: every magnet has two poles, a north and south. No matter how much a magnet is divided, even when into individual moving electrons, both poles continues to exist.
73
The intensity of the lines force is strongest at
the ends of the magnets (at the poles)
74
Properties of lines of Force
Properties of lines of Force
1.Continuous closed curves
2.Travel from north to south (outside magnet) & South
to north (inside magnet)
3.Curve towards the magnet
4.Never intersect each other
5.Concentrated at the poles of the magnets because
the magnetic field is stronger at both ends.
75
MAGNETIC INDUCTION:
•The effect a magnet has on an object without physical contact
•When a non-magnetized iron bar is brought within the
lines of force of a strong magnet, the dipoles will
temporarily align themselves with the lines of force
passing through the iron bar "paper clips" (until the
distance is too great for the induction to continue, in
which the last paper clip will fall)
*Paper clips= high permeability but low retentivity
But what we want in true magnet = low permeability
and high retentivity
76
PERMEABILITY:
the ease with which a material can be magnetized
(paperclip)
•When a ferromagnetic material is brought near a
magnet, the magnets lines of force deviate and
concentrate into the ferromagnetic material (will not
occur in a non-ferromagnetic material like wood,
glass, etc.)
77
RETENTIVITY
ability of a material to stay magnetized, retain state of magnetism (strong magnet)
These two factors are inversely proportional, they cannot be high in both.(permeability and retentivity)
78
1. FERROMAGNETIC: (simply magnetic)
```
• Iron, Cobalt, Nickel
• highly permeable
• greatly susceptible to induction
• Majority of their dipoles lying in the same
direction
```
79
2. PARAMAGNETIC:
•Platinum, aluminum
•Have low permeability and weak attraction to
magnetic fields
•These materials have only a slight majority of dipoles
in the same direction and there is little tendency for
the size of the dipoles to grow.
80
3. DIAMAGNETIC:
•Beryllium, bismuth, lead
•Weakly repelled by all magnetic fields, so weak that it
is easily obscured by other types of magnetic
induction
•Water is slightly diamagnetic
81
4. NONMAGNETIC:
•Wood, glass, rubber, plastic
•Not affected by magnetic fields
•Can NOT be magnetized
•Composed of atoms locked into crystalline or
molecular patterns, thus ionic and covalent bonds
and eliminating the ability of electrons to freely orient
themselves to external magnetic lines of force.
82
ELECTROMAGNETISM
| Definition:
creating magnetism through electricity
There's a magnetic field everywhere that carries electricity
Electricity and magnetism are the different aspects of the same force (electromagnetism), electromagnetism are the disturbances in space.
83
SOLENOID
when a conducting wire is looped (to form a coil), the magnetic fields from both sides join to double the magnetic field strength (magnetic flux density). A solenoid is when a current is flowing through this type of coil.
84
ELECTROMAGNET
when a ferromagnetic core is adding to a solenoid (increasing even more the flux density).
•Now there's a magnetic field around the iron core
and another magnetic field around the conductor (coil
of wire). The two magnetic fields are moving in two
different directions.
85
THE STRENGTH OF A SOLENOIDS & ELECTROMAGNETS ARE DETERMIND BY
* Number of loops (aka turns) of the wire
* Current strength
* Permeability of core
86
THE FACTORS THAT GOVERN THE EFFECTIVENESS OF SOLENOIDS & ELECTROMAGNETS ARE:
•Diameter of the coil
•Length of coil
•The current passing along the coil (if current
stops=no magnetic properties)
87
Electromagnets and solenoids are used as
Electromagnets and solenoids are used as remote-control devices in circuit breakers and temporary locks/detents (in radiographic equipment. Therefore, if there is no power we are unable to lock into/detent or even move the tube around properly.
*ELECTROMAGNETS ARE WHAT DETENT THE X-RAY TUBE!
88
ELECTROMAGNETIC RELAYS:
•Similar to circuit breakers
•Used to PROTECT RADIOGRAPHERS from electrical
shock by isolating control buttons on the x-ray
console from the actual circuit in which high voltage
is flowing.
89
1. Right Hand Rule: (generators)
Thumb = motion of conductor (direction of up or down)
Index finger = represents the magnetic field (north to
south)
Middle finger = direction of conventional current
90
2. Right Hand THUMB Rule:
(shows how a wire carrying current, generates a magnetic field)
```
Thumb = direction of current flow
Fingers = point towards the magnetic field
```
91
3.Right-Hand Thumb Rule for SOLENOID &
| ELECTROMAGNETS
Turn your hand as if you were to grip the
electromagnet
Your thumb will point to the north pole
Your fingers will point in the direction of current (up,
around, & back down
92
right hand grip rule
wrap fingers around solenoid in direction of current, thumb indicates north pole
93
ELECTROMAGNETIC INDUCTION:
•The principle that states the wire must have motion
relative to each other to induce electrical current
•Something needs to move to in order to create
electricity (magnet or coil)
94
3 ways to create the motion between lines of force and a conductor
1. move the conductor
2. move the magnetic lines of force
3. vary the magnetic flux strength
95
4 FACTORS THAT REGULATE THE STRENGTH OF
| INDUCED CURRENT
(when magnetic lines of force & conductor are in relative motion to one another)
1.Strength of magnetic field
2.Speed of the motion between lines of force and the
conductor (fast or slow)
3.Angle between magnetic lines of force and the
conductor (45°, 90° [high peak])
4.The number of turns in the coil
96
MUTUAL INDUCTION:
•occurs when two coils are placed in close-proximity
and alternating current is supplied to the first coil (as
an electromagnet) and therefore inducing a similar
flow in the second coil
•First coil is called the primary coil (supplied with
current)
•Second coil is called secondary coil (current flow
occurs because of the alternating current of the
primary coil)
•This follows the rule that moving lines of force from an
AC will induce electron flow in the wire which it
passes through
97
SELF-INDUCTION:
SELF-INDUCTION:
•Magnetic field produced in a coil of wire that opposes
the AC being conducted
•It is when ne coil of wire that induces voltage when
AC current is supplied, creating two opposing
magnetic fields that can induce an opposing voltage
in the very same circuit.
•Simply, two voltage sources from one coil, one from
the primary AC that is introduced, and then another
as a result, of the reversing of AC (not being able to
fully circulate)
98
INDUCTIVE RESISTANCE:
•The tendency of alternating current to oppose the
incoming supply of electrons (in self-induction)
•Inductive resistance measured in ohms
99
ARMATURE:
•The relationship between the direction of movement
of a wire coil (called the armature) and the direction
of the magnetic lines of force field and the direction
of the induced current.
•Use Flemings hand rules to figure out the different
directions of all the factors
100
Generators:
-Produce AC by motion of the armature (mechanical
energy)
•Device that converts mechanical energy into electrical
energy by using the principle of electromagnetic
induction.
•As the wires of the armature rotates(motion), they cut
through the magnetic lines of flux from the magnets
and produce electrical current.
101
• COMPONENTS OF A GENERATOR:
1.Armature: Loop of wire (in the middle)
2.Magnetic field: two magnets (on the sides)
3.Form of mechanical energy: to move wire through
the magnetic field.
Types of generators: windmills, nuclear plants, solar panels, hydro water plants etc.
A Generator MUST have these 3 components in order for it to work
Other components:
•Slip rings and brushes: permits the circuit to remain
stationary while the armature rotates without
breaking the electrical current. Connects to each end
of the armature wire.
102
Sine wave:
Type of curve produced by an AC generator. The sine
wave illustrates one complete turn of the armature.
•One sine is the complete negative and positive loop
60 sine waves = 120 humps (neg and pos. loops) in 1
second.
103
The frequency of the sine wave is determined by the number of cycles per second (cps).
•There are 60 sine waves in 1 second.
•Hertz(Hz): Unit of frequency. 1 Cps=1H. In the USA we
use 60 hertz cycles
104
4 Factors that regulate the Strength of Induced EMF
1. The strength of the magnetic field
2. The speed of the motion between lines of force and
the conductor
3. The angle between the magnetic lines of force and
the conductor
4.The number of turns in the conducting coil
105
3 Ways to Produce EMF in a Wire
1.Move a magnetic field across a stationary wire
2.Move a wire (conductor) through a stationary
magnetic field (principle of generators)
3.Vary the magnetic flux strength across a stationary
wire (principle of transformers)
106
Current is produced in two different directions:
•When the wire is moving up, current is going into the
board(page)
•When the wire in moving down, current is going out of
board (page)
•The direction is going to depend on the relationship
on the way the wire is moving and the magnetic field
107
GENERATORS LEAST AMT. OF TIME
Single Phase 1/120
3 Phase 1/360
High Frequency 1/1000 or 1ms
*As we increase the pulses, we get a shorter exposure time.
108
Single phase
only had 1 coil of wire. (Inefficient because the EMF builds up and then drop down to 0 before it goes back up again. 90-degree is the highest peak, the maximum amount of energy, so we had a lot of the values in between. This why motion was an issue before because they could take an exposure quick enough Ex. Peristalsis, babies, etc.)
109
3 phase has
-3 coils in the middle, creates more electricity, but
difficult to use (used in 80's but no longer)
•Least amount on a 3 phase 6 pulse would be 1/360 of
a sec (1/60 divided by 6)
•Least amount on a 3 phase 12 pulse 1/720 of a sec
(1/60 divided by 12)
110
Modern Units
High frequency, has more wires
•Instead having the EMF drop down to 0, we have a
more constant potential sine wave.
•Energy will get to the peak much quicker and never
drops back down to 0
•High freq. generators have a rectified sine wave
111
Rectification
Rectification
•Process that converts alternating current into
pulsating direct current
•Some rectifiers can suppress the negative sine wave
or completely invert it and put it on top.
112
MOTORS
Convert electrical energy into mechanical energy
3 components of a motor
1. Armature
2. Magnetic field
3. Electricity
Coil will turn because of the magnetic field. The coil supplied electrical current, creating a magnetic field around it.
When the magnetic field around the wire and the magnetic field of the magnets outside are going in the same direction, they repel each other, and this causes the wire to move.
113
The stator and rotor are induction motors because the rotor in the middle turns because of the magnetic fields of the stators on each side (2 stators).
•Stators are the "magnets"
•Rotor is supplied with the electrical current.
•Rotor moves because the magnetic field around it and
interacts with the magnetic field of the stators, thus
making it turn = electromagnetic induction
114
Galvanometers
they work on the motor principle
• If connected in series, they measure mA
• If connected in parallel, they measure kilovolts
• Work with DC only
115
Dynamometers:
* If connected in series, they measure mA
* If connected in parallel, they measure kilovolts
* Works with AC only
116
Transformers
Work on the principle of electromagnetic mutual induction:
•Two coils wire with a soft iron core
•The two coils of wire are placed in close proximity of
each other, because of the AC that is coming into the
first coil, we will induce similar current into the 2nd
coil = mutual
•Transformers need to work with AC because they
need to be constantly changing direction
117
Component of Transformers:
* 2 coils of wire
* Soft iron core
* Source of AC attached to 1 wire
118
Step-Up Transformer:
•Increase voltage and decrease amp
•Increases voltage because primary coil has LESS
number of turns than secondary coil, we will get twice
as voltage on the secondary coil.
119
Step-down Transformer
* Decreases voltage and increases amps
| * Decreases voltage because primary coil has more turn than the secondary coil
120
Transformer Cores:
1 . Air core- least efficient.
No iron core
Simple arrangement of 2 coils in proximity
2. Open Core- Similar to air core
Coils filled with iron core
3. Closed core- used in x-ray
Directs lines of force from primary to secondary cores
toward each other.
4. Shell type- Most efficient
Converges inside and outside lines of force through
an iron core
Primary and secondary coils are wrapped together
121
I2R / Copper loss
```
inherent resistance to current flow that is found in all conductors, this will always happen, we will always have resistance in any conductor, no matter what
How to fix it:
• Use a bigger diameter
• Less length
• Cooler temperature
• Change the type of conductor
```
122
Hysteresis loss/ Lagging loss
happens because we stop the spinning and starting again, we are constantly expanding and collapsing the magnetic field
*minimized by using silicon iron as a core material
123
Eddy Current loss
produced in any conductive material that is subjected to a change in magnetic field
• minimized by using laminated core
124
AUTOTRANSFORMER
•Selects a pre-determined amount of kV (that will be
sent up to the step-up transformer)
•Uses the principal of electromagnetic SELF induction
(because it only has 1 coil & 1 core)
•Used to vary the incoming line voltage to the correct
level of high voltage that we need for the step-up
transformer
125
CAPACITOR
•Stores large amount of energy.
•Composed of 2 insulated metal plates with opposite
charges that are attached to a battery
•the repulsion between the charges on the 2 plates
permits a greater number of electrons to be stored in
each.
•Dielectric: Insulation between the plates.
•Value of energy (electron stored) is determined by the
insulating ability, plate size and distance between
plates.
•Capacitor must be charged in order to operate.
Ex. Portable
•It accepts a charge until it equals DC voltage
126
Rectification
the process by which alternating current is changed to pulsating direct current.
127
2 Types of rectifiers:
1. solid state semiconductor diode (new)
| 2. vacuum-tube rectifier (old)
128
Diode
a rectifying semi-conductor, made by sandwiching a p-type semiconducting crystal and an n-type semiconducting crystal to form a p-n junction. This creates a one-way street for electrons
129
Thyristor or silicon-controlled rectifier (SCR)
is a more complex semi-conductor used for high speed switching of the primary high voltage x-ray circuit.
•SCR is actually a general electric name for a specific
type of thyristor.
•two p-type and two n-type (x-ray tubes have 4 diodes
that work two at a time, could have more but not less)
130
SCR happens in one of two ways
-suppressing the negative phase of the sine waves
(half wave rectification) [no longer used]
-inverting the negative phase of the sine wave (full
wave rectification)
131
Main circuit
* Supplies the x-ray tube with properly modified power
| * Its purpose is to produce x-rays
132
Filament circuit
* Supplies the filament of the x-ray tube with properly modified power
* It purpose is to create thermionic emission/cloud
133
x-ray History:
1913: Hot Cathode Tube by Dr. Coolidge
134
X-Ray Tube
•consists of a cathode and anode enclosed within a
glass envelope and then a protective housing.
•converts electrical energy into mechanical energy
(power source needed to operate)
•is inefficient < 1% x-rays, 99% is heat.
135
Cathode:
Cathode: negative side of the tube
Function of Cathode:
1. to produce a thermionic cloud
2. conduct high voltage to the gap between cathode
and anode
3. focus the electron stream as it is projected towards
anode.
Cathode: negative side of the tube
Function of Cathode:
1. to produce a thermionic cloud
2. conduct high voltage to the gap between cathode and anode
3. focus the electron stream as it is projected towards anode.
136
Cathode assembly consists of:
* Filament
* focusing cup
* associated wiring
137
Filament
thin thoriated tungsten small coil of wire
Function of filament: to provide sufficient resistance to the flow of electrons so that the heat produced will cause thermionic emission.
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0.1 - 0.2 mm thick
1 - 2mm wide
7 - 15mm long
filament length and width impact recorded detail
Tungsten selected due to:
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High melting point
Difficult to vaporize
Rhenium and molybdenum
Also good choices
138
Thermionic emission
when the filament gets sufficiently hot enough to boil off electrons (electrons are freed from the atoms in the wire)
139
Thermionic cloud
the accumulation of boiled off electrons that are in the focusing cup
The thermionic cloud is driven towards the anode when the high voltage is released at exposure.
140
Tungsten
material of choice because: 3 Hs:
• High atomic number (74)
• High melting point (difficult to vaporize)
• Heat-conducting ability
• Min. Of 2,200 degrees Celsius needed to exhibit
significant thermionic emission
• 3-5 amps necessary to heat up filament. & cause
thermionic emission
141
Focusing Cup
shallow depression in the cathode assembly designed to house the filament, holds thermionic cloud (herd the sheep)
• Made of nickel
• Purpose: to compress the thermionic
cloud as it is driven toward the anode.
• Low negative potential
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Dual Focus/Biased Focusing cup
x-ray tubes that have dual filaments.
•This maintains the cup at a more negative voltage
than the filament.
•Causes the exiting electron beam to be more
"focused" into a narrower beam to go to the anode
target.
143
Space Charge effect:
| phenomenon
the phenomenon that occurs when the boiled off electrons build up in the filament area, their negative charges beginning to oppose the emission of additional electrons. No matter how much you go up in mA, there will only be a certain number of boiled off electrons created. This is why x-ray tubes have a limit of 1,000-1,200 mA
144
Anode
positive side of the x-ray tube
Function of anode:
•serves as a target surface for the high-voltage
electrons from the filament (therefore source of x-ray
photons)
•Conducts the high voltage from the cathode back
into the x-ray generator circuitry
•Serves as primary thermal conductor
145
Anode target
where the high-speed electrons from the filament are suddenly stopped (resulting in x-ray photon)
146
Anode assembly: consists of
1. Anode
2. Stator
3. Rotor
147
Rotating anodes
Rotating anodes range from 5 to 13cm
•created in 1936:
•enhance by rhenium alloyed tungsten.
•Turn during the exposure-thus presenting a much
larger target area. (the faster the anode rotates, the
better heat dissipation). Used now in all diagnostic
radiography.
•Composed of molybdenum
•Has a dynamic target area
•High speed rotating anode have higher heating
capacities than regular speed-anodes (50 % greater)
*specialized anodes are backed up with: molybdenum
and graphite. (graphite double heat loading)
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Stationary anodes
Stationary anodes
•Have a static target area
•are now limited to now dental office/units, no high mA
needed
•Composed of rhenium-alloyed tungsten imbedded in
a 45-degree angled end of a copper rod.
•Rhenium Z# (75)
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Focal track target
•Composed of rhenium-alloyed tungsten
•The tungsten withstands the intense amount of heat
•The rhenium provides greater elasticity when the
focal track expands rapidly due to the intense heat.
150
Mammography uses molybdenum focal track
•Atomic # 42
•Used because ability to emit more uniform rang of
lower-energy photons
151
Beryllium
glass window
152
Pitting of the anode:
•Occurs during normal use of rotating anode,
eventually leading the focal spot roughening/pitting
due to vaporization
•Occurs because of defect in one of the ball bearings
(that’s why we don’t router for no reason)
153
saturation current (phenomenon)
-the higher the kvp the greater the # of electrons from
the space charge are driven to target
-extreme kvp levels will drive ALL electrons to the
anode
-saturation occurs when there are no more thermionic
electrons to drive the anode
-at this point and increase of kvp WILL NOT increase
the tube mA.
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protective housing
Housing made of lead-lined cast steel
NCRP Leakage radiation limit
100 mR/hr. at 1 meter
•Primary beam exits window but the rest of unwanted
photons are absorb by housing
•Composed of cast steel, lead lined, insulating oil
(diaelectric oil)
• Purpose is to absorb leakage radiation and to
cushion the x-ray tube against rough handling
155
expandable gasket (housing)
when tube heats up, it spends to help cool down
156
dielectric oil (housing)
-insulates, promotes cooling, sometimes circulating
through heat exchanger
•Oil also absorbs the heat that occurs during x-ray
production
-Air fan
157
The envelope
Pyrex glass, or metal
10” long,6” central diameter, 2” peripheral diameter
•Metal envelopes becoming popular recently (because
eliminates tungsten vaporization)
•Purpose is to maintain the vacuum
•Contains window, (area where the primary beam exits)
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3 main things to produce x-rays
- filament: to accelerate electrons
- high voltage
- target: to decelerate electrons
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Speed of Rotor
3,200 – 3,600 common rotor speed
| 10,000 – 12,00 high rotor speed
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warm up procedure
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Gradually warms the anode
Prevents cracking
Helps maintain the vacuum
Stress relieved anode
•FAILURE TO WARM-UP, can cause the entire anode to crack (because molybdenum will absorb the heat too rapidly and excess expansion capability)
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161
Tape Measure
is installed to the bottom of the tube collimator- it actually begins at 12 cm because x-ray tube housing has an imaginary line dawn on them to indicate the exact level of the target within.
162
Focal Track
Circular path on the target that will be impacted by the electron beam at one time
163
the target area
the precise point where where x-ray photons are created
164
Actual focal spot
the physical area of focal track that is impacted
165
Effective focal spot
the area of the focal spot that is projected out and towards the object being radiographed
166
Line-focus principle
used to reduce the effective area of the focal spot.
Effective focal spot size is controlled by the size of the actual focal spot (which is controlled by the length (size of the filament) AND the anode target angle. Both are directly proportional.
When the target angle is less than 45 degrees, the effective focal spot is Smaller than the actual focal spot.
Most common diagnostic radiography target angle is 12 degree. Some tubes angle range from 7 – 12 degrees.
167
Anode Heel Effect
Trade-off of the Line Focus Principle
Angled target
Anode heel is in path of x-ray beam
Intensity of beam less on anode side, greater on cathode
168
in which direction should the cathode be placed for an anteroposterior examination of the thoracic vertebral column? (anode heel effect)
because the inferior thoracic region is more dense, the cathode's more intense beam should be be positioned inferiorly to help increased the exposure in that region
169
Off-Focus Radiation
Is created by photons that were not produced at the focal spot
170
The Stator
•Induction-motor electromagnets that turn the anode
•Only part of cathode or anode assemblies that is
located OUTSIDE the vacuum/glass envelope
•Electromagnetic effect causes the rotor to turn, that is
why it's able to function outside.
•If the stator fails, the rotor will not turn and cause
melting/pitting
171
The Rotor
•Located inside the stator and inside the envelope
•Composed of a hollow copper cylinder or cuff that is
attached to the anode disk by a molybdenum shaft
•The cuff is the true rotor that is affected by the
electromagnetic field of the stator, causing it to turn
•Inside the rotor contains silver-plated steel ball bearing
around a shaft this is anchored to the envelop.
•Ball bearing are silver-plated because silver acts as a
high-temperature lubricant
•When the exposure switch Is depressed when
routering, the sound that is heard is the ball bearings
turning
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Filtration
any material designed to absorb photons from beam
(low-energy), eliminate soft x-rays
Added between x-ray source & patient
Aluminum most common
Expressed in terms of thickness of aluminum (Al/Eq)
Also expressed as half value layer (HVL)
173
Inherent Filtration
* Dialectric oil
* Glass envelope
* Glass/beryllium window
* Inherent measured in 0.5-1.0 mm of Al/Eq
174
ADDED
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Any filtration that occurs outside of x-ray tube housing and before image receptor
Collimator device (including the silver mirror)
Added filtration = 2.0 mm Al/Eq
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175
total filtration
* Combination of added and inherent
* NCRP Recommended :
* < 50 kVp – 0.5 mm Al
* 50 – 70 kVp – 1.5 mm Al
* > 70 kVp 2.5 mm Al
176
Any radiation that escapes the housing is called
Leakage radiation
| Leakage radiation must not exceed 100 mR/hr at 1 meter
177
Rating charts/Tube rating charts
•Most valuable because provides a guide regarding
the maximum technical factor combinations that can
be used without overloading the tube (plotting in
milliamperage, kilovoltage and time) anything to the
left or BELOW= safe. To the right or ABOVE = NOT
safe
178
Anode cooling charts
Anode cooling charts
•Permit the calculation of the time necessary for the anode to cool down enough for additional exposures
•Cooling charts are calculated in heat units
(rectification constants)
Single phase = 1.0
Multi-phase 1.35
High Frequency = 1.40
Heat unit (Hu) calculated as kVp x mA x time x retification constant
179
Conditions needed for x-ray production
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Conditions needed for x-ray production
• Separation of electrons
• Concentration of electrons (focusing cup)
• Production of high speed electrons
• Sudden stoppage of electrons
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180
in which direction should be the cathode be placed for an AP examination of the thoracic vertebral column?
because the inferior thoracic region is mire dense, the cathode's more intense beam should be positioned inferiorly to help increase the exposure in that region.
181
secondary radiation
Radiation emitted from the atoms of matter after x-ray photon from the primary beam interacts with matter (characteristic radiation).
182
primary radiation
a.k.a. useful radiation
Consists of x-ray photons directed through the window of x-ray tube in direction toward patient.
The x-ray bean Before it interacts with patient.
X-ray photons in primary beam are called incident photons
183
Mobile radiography
| history
1950- the collimator
1960- The more modern x-ray unit
1970- power driven
184
Digital Detector/ Mobile equipment
What we use in the hospital is mobile not portable even though that what we call it
185
When looking for Air fluid levels
CR must be horizontal with the floor.
CR must be parallel with the Air Fluid Levels.
186
Siemens's mobile digital
instant image
187
power drive
Self-propulsion for mobile unit
Dead-man switch (only move when pressed)
Must use caution when piloting equipment
188
power supplies (mobile)
Portable light duty units (hand-held)
110V or 220V outlet
Full power mobile institutional units
Battery operated
Rechargeable Battery in 110 V or 220V outlets
189
Generator (mobile)
Battery operated units – produce output that is essentially high frequency.(never drops to zero)
Must be plugged into wall outlet to recharge battery
110 to 120-V wall outlets
190
special considerations (mobile)
Communication
Manipulating equipment
Positioning and pathology
191
communication (mobile)
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Park mobile unit outside patient’s room
Establish rapport
Get patient’s permission to do the exam
Explain the procedure
Move items that will be in the way
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192
manipulating equipment (mobile)
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Equipment power supplies
Oxygen tubing
Intravenous lines
Catheters, etc.
Don’t bump the bed or your head
Radiographer’s responsibility to return all items to their original locations
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193
Radiation Protection Considerations (mobile)
shielding and distance
ask everybody to leave when exposing
never place hand in primary beam
avoid repeats
194
positioning and pathology
Remove all radiopaque objects
Move lines from imaging field if possible
Limit coverings to single, smoothed layer
195
Special technical factor consideration
kVp: functions as normal x-rays
mAs: before not possible, now yes
Distance
Grids: use low ratio
196
When looking for Air fluid levels
CR must be horizontal with the floor.
CR must be parallel with the Air Fluid Levels.
197
AEC = Automatic Exposure Control
-Created by Russell H. Morgan in 1942noy used in
hospitals until 70's
-Also referred to as photo-timing
-The only thing we set on AEC is KVP (to control
contrast)
-Radiographer chooses kVp and also which ionization
chamber(s) to use (to control density)
-The AEC will choose and terminate exposure time,
therefore will also as a result choose mAs
-Main function/purpose of AEC is to eliminate the need
for radiographers to figure out exposure time
-AEC WORKS ON PRINCIPLE OF IONIZATION
-AEC terminates exposure when adequate amount of
ion pairs are created in the ionization chambers
198
creative positioning (AEC)
-involves manipulating the cells when tissue do
completely cover them, to avoid exposure:
-deactivation of an uncovered cell, however not a
solution
-only attempted by experienced radiographers
199
Minimum reaction time/ Response time ( do not confuse with mA timer of circuit) (AEC)
- length of time needed for AEC system to respond to
radiation and for the generator to end the exposure.
- the shortest exposure time that the system can
produce
less than 0.001 second with modern AEC
200
back up time (BUT)
-maximum length of time the x-ray exposure continues
when using an AEC system.
-safety mechanism
-same can be manually selected
-should be set at 150% of anticipated exposure time
-usually preset
-maximum exposure per US public law 90-602
*600mAs at or above 50kvp
200mAs below 50 kvp (mammography)
201
Two factors that affect/determine the length of exposure time.
(AEC)
1.KVP
-Sending more high energy photons that will create
the ionization faster = faster exposure
2.Back-up time
202
KVP & AEC
-select the appropriate kVp to insure adequate
penetration and appropriate scale of contrast
-should be at least the minimum kvp to penetrate part
-kvp selected determines the length of the exposure
time.
203
MAS readout display (AEC)
-after exposure taken, the mAs displayed for the
image)
-radiographer should keep track to recreate good
images with a good technique & proper position, this
will lessen the need to repeat
204
density controls (AEC)
-permit adjustment of preset radiation detection values
-varies length of exposure time
-buttons on control panel such as -1,-2,+1,+2
-these usually change predetermined exposure level about 25%
-should not be used to compensate for changes in part
thickness
-AEC does this automatically
-pathologies (emphysema use -1 or -2 settings)
205
Patient with severe osteoporosis. Using AEC (anything with the – decrease density, anything with the + increase density).
– 1 decreasing exposure by 25%
206
Subject Density and Contrast Problems (AEC)
-Occurs whenever an unexpected density is present or
expected density is absent
Such as:
-fluid in lungs
-emphysema = reduce kVp from 80 → 60 kVp
{portable}
-osteoporosis = if severe, reduce from 80 → 60 kVp
207
Collimation ( AEC)
-Collimating too close to the activated chamber should
be avoided, might result in overexposed image
-inadequate collimation may result in an
underexposed/light image
-undercutting
208
Anatomically Programmed Radiography (APR)
Chooses the body part in the console and that will automatically give you the technique for the average size body part.
-computerized technique charts that use AEC
capabilities
-manual override (you can increase or decrease kVp)
209
creative positioning (AEC)
-involves manipulating the cells when tissue do
completely cover them, to avoid exposure:
-deactivation of an uncovered cell, however not a
solution
-only attempted by experienced radiographers
210
IMAGE INTENSIFICATION (Fluoroscopy)
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Dynamic examination
Active diagnosis
Domain of radiologist
Fluoroscope
Invented by Edison in 1896
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211
Purpose of Image Intensification
The images were horrible until image intensification was invented, what image intensification does is that it intensifies the x-rays through the components in the image intensification tube (crystals, chemical components). Also, lower patient dose for the patient.
With fluoroscopy we are able to do/see:
• Static Imaging
• Dynamic imaging (organs moving)
• Record of physiology of vessels, and organs etc.
212
Legalities and Ethics of Image Intensified Fluoroscopy
The use of image intensified fluoroscopy is under the control of the Radiologist only!
Rad. Technology Board of Examiners in NJ (RTBENJ):
“Radiologic Technology Board of Examiners at their 12/80 meeting re-affirmed their prohibition of licensed x-ray technologists utilizing fluoroscopic equipment”
Public Law 1968, c.291
“People are protected from harmful effects due to excessive and improper exposure to ionizing radiation”
213
fluoroscopic requirements
Fluoroscopic x-ray tube
Image Intensifier tube (tower/carriage)
TV camera tube (Television monitor) or Charge Coupling Device (CCD) (digital)
214
Fluoroscopic X-Ray Tube
Similar to the x-ray tube
Found below the table surface or
May be the same tube used for creating overhead images
Can move transversely and longitudinally, but NOT vertically
changes the required SSD
215
Similarities between fluoro and conventional x-ray tubes
Vacuum
Diode
“Dead man’s switch” for exposure activation
Produces ionizing radiation
216
differences between fluoro and conventional x-ray tubes
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Operates using low mA values (0.5 mA to 5.0 mA)
Longer exposure times (max 5 minutes)
Minimum source-to-skin distance:
12” for mobile (C-arm) equipment
15” for stationary /fixed systems
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217
Carriage
| fluoro
•The carriage and fluoroscopic x-ray tube are
connected to form “c-arm” configuration.
•Structurally, the carriage is the image intensifier tube
218
Over the Table Carriage (fluoro)
* Bucky slot cover would close when it thinks you getting ready to do fluoroscopy (or you have to close it manually)
* Move the bucky tray to the end of the table because if you don’t you would block the visualization of the images.
* For static images, they can put the cassette in the spot-film cassette. They can take up to 4 images in one cassette because the images are very small. We see the images on the monitor, but also capturing the images statically on the spot images.
* Regulations to how much lead should be in the drape (curtain), bucky slot cover, lead apron, they should contain a minimum of .5 mm of lead equivalent.
219
Image Intensifier(II) Tube (fluoro)
Converts the exit beam into bright, visible light.
20 cm (8”) long
Requires 25,000 V or (25 kV) to speed the electron flow from input to output screens.
Mounted in a metal cylinder (radiation safety)
• Parts:
• input screen/ input phosphor*
• Photocathode*
• electrostatic focusing lenses*
• anode/ focal point*
• output screen/ output phosphor
220
Input Screen/Input Phosphor
0.1 – 0.2 mm layer of sodium
Activated c-Cesium iodide (CsI)
Tube-shaped phosphors
Converts x-ray into visible light
221
Input screen Diameters
Dual Field /Dual Focus tube
e.g., 23 cm (9”) and 15 cm (6”)
Triple Field
Quad Field
Multi-field
The size of the input screen profoundly affects magnification of the fluoroscopic image.
222
Photocathode
Bound to the input screen
To prevent the loss of sharpness by divergent light
Made of Cesium and Antimony compounds*
Converts visible light into electrons*
Released electrons are directly proportional* to the light received from the input screen.
223
Electrostatic Focusing Lenses
Metallic plates placed along the length of the II tube
Plates are charged
Guides the stream of electrons from the input to the output side of the II tube
224
Focal point and anode
Focal Point
Specific point in space where the electron stream converges and reverses.
Anode
Directly after the focal point.
Circular metal plate with a hole in the center.
Hole allows electrons to pass through to get to output screen.
225
Output Screen/ Output
| phosphor
```
Situated on output side
Also a glass fluorescent screen
Zinc cadmium sulfide phosphor
1” diameter (2.54 cm)
Connected (coupled) to TV camera tube
High conversion efficiency
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226
MAGNIFICATION FLUOROSCOPY
The process of using magnification/size distortion to better visualize anatomy.
Focal point is changed to a smaller input screen diameter to produce magnification.*
Controlled at fluoroscopy carriage
Capable of 1.5 to 4 times magnification
Yields a higher patient dose.*
227
Process of magnification
Smaller input diameter is selected.
Shifts to magnification Mode
Focal point shifts closer to the input screen*
Voltage increases to a point that is higher than 25 kV
Creation of a dim image causes the fluoro x-ray tube to increase the mA value*= increase patient dose
A smaller input diameter makes fewer electrons
Therefore, a dimmer image is made (fewer electrons)
228
Calculating Magnification
What is the magnification mode when an II tube with an input screen of 23 cm that is using a 13 cm diameter area during magnification?
divide 23/13
229
Total Brightness Gain
A measurement of the increase in image intensity achieved by an II tube
Determined by two factors:
Minification Gain & Flux Gain
Brightness gain = Minification gain x Flux gain
230
Minification Gain
•Principle that clearly demonstrates the effect of light
production when comparing the diameters of the
input and output screens:
Input diameter2 /Output diameter2
•Minification is going to play a role in brightness gain.
231
Flux gain
Measurement of conversion efficiency of output screen
One electron strikes output screen
If 50 light photons are emitted by each electron
striking output phosphor,
Flux gain = 50
Conversion efficiency is a measure of image intensifier performance
232
Image Quality
Contrast
Resolution
Distortion
Quantum Mottle
233
Contrast
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Controlled by amplitude of video signal
Digital systems use post-processing
Window width and filtering algorithm
Affected by:
Scattered ionizing radiation
Penumbral light scatter
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234
Resolution
Fluoroscopic resolution not as good as static radiography.
Varies depending on geometric factors
S I D, O I D, minification gain
C s I image intensifiers capable of ~2 l p/mm
Edges of image intensifier have lower resolution due to vignetting
Whereas Digital fluoro systems achieve
3 l p/mm or better.
235
Distortion
Size Distortion
Affected by same parameters as static radiography
Primarily O I D
Shape Distortion
Geometric problems in shape of the II input screen
Concave shape helps reduce distortion
Vignetting or pincushion effect
Not a problem with T F T matrices
Uniform resolution across flat panel detector array
236
Quantum Mottle
Blotchy, grainy appearance
Due to insufficient x-ray exposure to input phosphor
Reduce QM - increase total exposure to intensifier input phosphor by:
Increase m A
Reduce distance between patient and image intensifier
Increase k V p
237
VIDEO VIEWING SYSTEMS
Digital fluoroscopic systems
Most commonly used
Use flat-panel displays
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Video tubes
The original systems before digital
Video camera attached to output phosphor
Fluoro video camera uses CCD
Display monitor for viewing
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238
DIGITAL FLUOROSCOPY
Achieved with use of high-power generator
Pulses x-rays produced in fluoro x-ray tube in sync with the detector signal
Pulses of signals are received by the image processing unit.
Image intensifier output screen coupled to T F Ts
Newer systems replace the non-digital image intensifier with amorphous selenium (a-Si) flat panel T F T detector
200 - 400 microns D E L size (2-3 lp/mm)
