X-ray Machine, X-ray Quality, and Attenuation Flashcards
EXAM 1 PREP
__ ____- Flow of electrons through a wire or circuit.
- Source of energy usually 110 or ___ Volts
Electric Current
220
Electrons flow in one direction
Direct Current
Electrons travel in one direction, stop and then reverse and go in the opposite direction.
Alternating Current
Electricity cylces in an __ ___- the curve above and below a horizontal line
Alternating Current
_ ___ necessary for production of x-rays in the x-ray tube
- ___ Circuit
- High __ Circuit
2 Circuits
Filament Circuit
High Voltage Circuit
Step Down Transformer
Heats the filament circuit
Controlled by Milliamperage (mA)
Fewer turns in second coil than primary coil
Decreases voltage from 110 to 3-5 volts
Step-up Transformer
Controls the high voltage circuit
Controlled by Kilovoltage
More turns in the secondary coil than the primary coil
Changes 110 volts to 65,000-100,000 volts
Gives the ability to alter kilovotage of the x-ray machine
A single coil around a iron core serves as the primary and secondary coil
Auto Transformer
MA (Milliamperage) determines
Why does it effect Quantity?
the # of photons in a beam
kVp (Kilovolt Peak) determines
kVp also influences the Quantity why?
the energy of each photon, ie Quality
Also influences quantity because
Distance of the Xray beam is the
size of the beam
Rate of the xray is the
exposure time ie ///// Quantity. More time more xrays
Does exposure influence Quantity
Yes. Why? Because
A longer exposure time produces more xrays.
An increase increase in xrays produces a more intense beam
**mA + kVp+ Distance + Rate together =
Beam Intensity
Relationship between exposure time and mA
mA required for a given exposure time is inversely proportional to the exposure time
- HIGHER mA requires less exposure time
What is the equation to represent source-film distance effects on intensity
Inverse square law Original mAs (time) / New mAs (time)
=
Original SFD^2/
New SFD^2
Short Great penetration High energy High frequency Go through
Best xrays
Long Low penetration Low energy Low frequency Absorbed
bad xray
Filtration of xrays
Located in tubehead
aluminum selectively absorbes out useless lower energy photons
Half Value Layer-
the thickness of absorbing material (usually aluminum) necessary to reduce x-ray intensity by half its original value
Controls the size and shape of beam produced Metal cylinder or lead washer Shapes the x-ray beam Round BID Rectangular BID
Collimation
Restricts the size of the primary beam
Collimation
penetrating x-ray beam produced at the tungsten target of the anode that exits at the tubehead.
AKA- Useful Beam
Primary Radiation
created when the primary beam interacts with matter.
Includes soft tissue of head, bones of skull, and teeth.
Scatter Radiation- Form of secondary radiation resulting from an x-ray photon that has been deflected from its path by the interaction with matter.
Secondary Radiation
Secondary Radiation
A
B
C
Pass through
Absorbed
Scatter
Secondary Radiation __ ___ with no interaction producing dark areas on film (radiolucent)
-Examples- soft tissue, pulp, PDL
pass through
transfer of energy from x-ray photon to the atoms of matter through which the x-ray passes (approximately 30% of interactions with matter)
Produce light or white areas on film
Examples- cortical bone, enamel, metallic restorations
Photoelectric Effect
Absorbed Completely
Radiopaque
photon strikes a loosely bound outer shell electron of matter, and ejects is from orbit (ionization)
the x-ray photon loses energy and continues in another direction (including backwards)
If reaches the film it produces fog
scattered x-ray deflected from its passage through matter (approximately 62% of interactions with matter)
Compton scatter
Interaction of x-rays with patient
low energy photon has its path altered by matter and changes directions. (approximately 8% of interactions with matter)
X-ray photon undergoes change in direction without change in energy
Coherent Scatter
reduction in the intensity of the x-ray beam as it transverses dental tissues./ Absorption
High absorption of x-ray photons=____________
Low asborption of x-ray photons =
Attenuation
radiopaque areas on film- bone
Radiolucent areas on film-air
Factors Affecting Absorption
Wavelength:The energy of the xray photon
Density of Material
Thickness of Material
Atomic Number of Material: Higher atomic number= greater absorption - Aluminum=13 -Copper = 29 - Lead= 82
