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Radiolucent
Portion of the image that is dark or black
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Radiopaque
Portion of the image that is light or white
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Density
The degree of darkness or image blackening (ex. light image has little density, dark image has more density)
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Contrast
Refers to the many shades of gray that separate the light and dark areas
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High kV results in high or low contrast?
Low contrast
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Low kV results in high or low contrast?
High contrast
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3 professional goals in dental radiography?
Patient protection, operation protection, and patient education
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What three conditions must exist for x-rays to be produced?
- A source of free electrons (cathode)
- High voltage to impart speed to the electrons (kV)
- A target that is capable of stopping the electrons (anode)
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Cathode
- Negative electrode
- Tungsten wire/filament
- Focusing cup
- heats incandescent (red hot)
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______ is vacuum tube that produces X-rays an energy converter
X-ray Tube
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focal spot
- small area on the target on the anode toward which the electrons from the focusing cup of the cathode are directed
- x-rays originate from here
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Anode
- Positive electrode
- Tungsten target
- Copper stem/radiator
- 20* angle
- 1 direction = primary beam
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What happens when you push that button?
- You get the wave
- IONIZING radiation is produced
- Creates e- cloud of energy
- Heats = speed Releases the invisible x-rays in a Wave
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The anode contains a copper stem/radiator, what is the purpose of it?
Heats up and absorbs the generated heat (it is a good conductor)
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What is the purpose of the cathode?
To supply electrons to make the X-rays
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What is the purpose of the anode?
The tungsten target found inside stops/slows down the electrons (converting the kinetic energy into X-ray energy)
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Describe the process of producing radiation inside the tube head
- 1. Cathode creates a cloud of electrons (quantity of electrons controlled by the mA)
- 2. Tungsten wire/filament heats up and excites the electrons, shooting them into the anode
- 3. Electrons bounce off of the focal spot on the tungsten target found on the anode
- 4. Primary beam then shoots out of the PID
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Quality (energy strength) of the beam is controlled by what setting?
kVp
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Quantity (amount of X-rays/electrons) is controlled by what setting?
mA
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Port seal
Determines the size of the beam, exiting the tube head
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Lead Collimator
Restricts the beam once exiting the port seal
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What is produced in result of lead collimator restriction?
Primary/useful beam
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Central ray
The X-ray in the center of the primary beam
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What is the preferred wavelength in dental radiography?
Short and fast, primary beam is strong
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What wavelength should we stay away from as hygienists?
Long
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What determines the mA setting?
Patient's mass
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Voltage (kVp)
Force the electrons to push through the mass, penetration ability
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Amperage (mA)
- amount of current in tube and available # of free e-
- the Quantity (amount) of radiation affects how dark or light the whole radiograph looks.
- This is DENSITY.
- The denser the e- cloud (controlled by mA) the darker the image
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______ is x-rays of many different energies & must be filtered to allow only x-rays with sufficient energy to reach the oral structures
Polychromatic beam
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_____ = tube potential…. highest voltage to which the current in the tube rises during an exposure 1,000 V / (kVp – kilovoltage peak)
Kilovolt peak (kVp
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What happens if you increase the speed of e- in the tube ? Or increase the Voltage (kVp)?
- Too dark
- Lowers contrast (too grey)
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What happens if you Lower the speed of e- / voltage (kVp)?
Image increases in contrast and the image is too light
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_____ determines the speed of the e- and therefore the penetrability of the x-rays produced
kVp
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______ e- over to tungsten target & controls the amount of attraction of e- to the target (which is 1%) other 99% is absorbed in the tube (*slide 22)
KvP pulls
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What happens with a decrease in number of (e-)? Or a Lower mA?
Image becomes too grainy
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What happens when you increase # of e- in the conductor? Or UP the mA?
Image is too dark
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Long scale contrast
Low contrast, lots of grays (high kVp)
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Short scale contrast
High contrast, less gray and more black/white
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What contrast scale do we prefer in dental radiography?
Long scale contrast
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Describe the matter if the image was too dark (high density)
Matter was flooded with radiation
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Describe the matter if the image was too light (low density)
No radiation went through/penetrated through matter
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What type of radiation are we producing in the tube head?
Ionizing radiation
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Where do the electrons forming the electron cloud in the cathode come from?
We steal them! Taken from the most outer shell (L shell) of atom
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Bremsstrahlung Radiation (aka general radiation)
Majority and primary kind of ionizing radiation, radiation produced
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Secondary radiation
Beam hits the matter, however it is absorbed in the patient's soft tissue
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Scatter radiation
Radiation deflects, beam hits all directions while hitting matter
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What two factors determines the absorption of the X-ray beam?
Patient mass and energy of the beam itself
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Coulombs/per kilogram (C/kg)
Unit of electrical charge
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Gray (Gy)
Unit of energy deposited into the matter
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Sievert (Sv)
- Measure protection, biological effects with different types of radiation on a human
- ex. 1 xray = 1 factor = 1 Sv
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ALARA
As low as reasonably achievable
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What is the collimator size at the end of the PID?
2.75 inches
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What is the target? (Target Surface Distance)
Anode
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What is the surface? (Target Surface Distance)
Sensor
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______ are made up of atoms
ELEMENTS
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What is the distance? (Target Surface Distance)
Beam from target (anode) exiting the PID must go through the object (tooth)
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______ smallest part of an element
atom
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The innermost orbit or energy level is the __ shell, the next is the __ shell, and so on up to __ shells
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the number of positively charged protons is ____to the number of negatively charged orbiting electrons = ______
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____ atoms that have gained or lost e- (unstable)
ION
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____ Ion = loss of an e-
Positive
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______ Ion = the lost (-) charged e-
Negative
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____ – is the joining of a (-)e- and (+) proton
Ion pair
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____ - formation of ion pairs
Ionization
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Why is this IONIZATION important
¢When an atom is struck by an x-ray photon an e- maybe dislodged causing the -E to form. This creates energy in the form of incandescent (heat). (+) will try to find stability = ionizing radiation
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_____ = release and movement of energy through space
Radiation
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Any radiation that produces ions is called
ionizing radiation
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_______ The distance from the crest of one wave to the crest of the next wave
Wavelength
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_____ number of waves emitted per second
Frequency
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______ produce lower frequency (lower energy) and less penetrating power, and “soft radiatioN
LONG WAVE LENGTHS
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_______produce higher frequency (high energy) more penetrating power, and “hard radiation.”
Type of radiation we use.
SHORTER WAVE LENGTHS
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Properties of X-rays
- X-rays consist of electromagnetic bundles (quanta) the are called photons during Bremsstrahlung (or Braking) Radiation
- Are invisible
- Travel in straight lines
- Travel at speed of light
- Have no mass or weight
- Have no charge
- Interact with matter causing ionization
- Can penetrate opaque tissues and structures
- Now you know the reason why we need to be VERY CAREFUL
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_____= x-ray passes through matter and is weakened and disappears / the transferring of this energy is called ionization
Absorption
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4 probabilities exist with this ionizing radiation as it passes though a patient’s matter:
- No interaction = x-ray passes through, atom unchanged = < 9% of the x-ray beam passes thru without interaction
- Coherent scattering = e- vibrates/rattles without loss of energy < 8 % of the x-ray beam contains coherent scatter
- Photoelectric effect = the collision of e- and photons to form kinetic energy creating and ion pair< > 30% of the x-ray beam interacts this way with matter
- Compton scattering = partial e- interaction by ejecting an e- creating a new & weaker x-ray photon
- < > 60% of the x-ray beam interacts this way with matter
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