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88 Cards in this Set

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Definition of electomagnetic radiation
The propagation of energy thru space as oscillating electromagnetic fields.
Physical characteristics of EM radiation
No mass
No charge
Travels a speed of light
Types of EM radiation
radio waves
infrared
visible light
UV light
x-rays
γ-rays
Differences between types of EM radiation
All same speed.
Differ in wavelength/frequency.
x-rays/γ-rays=shortest wavelengths,
radio waves=longest wavelength
Speed of light
(defined by wavelength)
c= wavelength/frequency
Energy as related to wavelength
E α 1/wavelength
as wavelength increases, energy decreases
Origin of x-rays
from outside the nucleus by interactions between high speed particles
Origin of γ-rays
from inside the nucleus of spontaneously decaying atoms
Parts of basic x-ray tube
Filament
Target
Glass tube
Anode
Cathode
Filament
thin coiled wire that serves as the source of electrons
made of Tungsten
Part of the Cathode assembly
Thermionic Emission
Forcing a low voltage current through the filament (against its resistance) generates heat.
Heat results in the release of free electrons.
Focusing cup
Negatively charged cup surrounging the filament, prevents generated electrons from dispersing
Voltage
(potential difference)
Negative cathode-positive anode
Pulls and accelerates electrons away from filament, towards target
Voltage used for diagnostic procedures
40-140 kVp
Kilovolts peak
Voltage used for therapeutic procedures
1-4 MV (megavolt)
Target
Part of the anode.
Contains the focal spot
Focal Spot
Area of the target where the actual interactions that produce the x-rays occurs
Housing
the glass/pyrex tube that holds the vacuum.
Surrounded by a lead shield.
Purpose of the vacuum
Prevents electrons from interacting with atoms in the air.
Window
a small port in the lead shielding that allows the "useful beam" to escape
Types of interactions
Transition
Bremsstrahlung
Transition interactions
Characteristic
x-rays in a very specific energy range
Brehsstrahlung interactions
General
X-rays in a broad range of energies
Efficiency of x-ray production
very inefficient
99% of incoming electron energy is converted to heat, only 1% is converted to useable x-rays
Effective focal spot
The apparent size of the focal spot from patients point of view
Effect of increasing the size of focal spot
greater output capability,
greater heat dissipation
Effect of decreasing the size of the focal spot
greater detail of image,
done by making angle of target steeper
Two type of anodes
Stationary
Rotating
Uses of stationary anode
Portable diagnostic equipment
Therapy (when auxillary cooling is incorporated)
Limitations of stationary anode
Lower output, due to limited ability to dissipate heat
Uses of rotating anode
Fixed diagnostics
Special procedures
Low portability/portability-when greater output in required
Value of a rotating anode
Greater output capability, due to increased ability to dissipate heat
Filaments of rotating anode systems
most have two filaments
one for large focal spot, the other for small focal spot
Quantity of x-rays
= # x-rays in the beam
Quality of x-rays
= energy of x-rays in the beam
Characteristics of x-ray quality
Penetrability-higher quality=higher energy=more penetrability
Control of x-ray quality
Controlled by the kVp of the instrument
Control of x-ray quantity
Controlled by kVp-energy of electrons in the beam=amount of interactions
and mA-current in milliamps=rate of electron emissions
mAs
Current * exposure time
influences the quantity of electrons in the beam
kVp
controls tube voltage
influences the quality (mainly) & the quantity
Target loading chart
Chart used for older equiment to ensure you don't damage the tube by using settings that are too high
x-ray filters
a sheet of aluminum/copper placed between the x-ray tube and the collimator
Purpose of x-ray filters
Lower radiation exposure of the patient since low energy x-rays would otherwise be absorbed by the patient
Function of x-ray filters
To selectively remove low energy x-rays from the primary beam
Collimator
adjusted the size of the x-ray field
Function of the collimator
limit the x-ray field to only the areas of interest.
Enhance image quality by absorbing scatter radiation
Proper collimation
Should have a white border around x-ray field.
Limits the radiation exposure to patient & holder
Function of Grids
Reduce the amount of scatter radiation striking the x-ray film.
Compton Scattering
Most important form of scatter radiation.
Caused by a primary x-ray photon hitting a dislodging a electron in the patient, turning it into a secondary x-ray, which strikes film randomly
Effect of scatter radiation
Produces fog= a decrease in image quality, overall grayness to the film
Factors affecting amount of scatter radiation
tissue density
total volume being x-rayed
-field size
-thickness of patient
As each increases scatter increases.
kVp
Grids
Plates with alternating lead & aluminum strips. 80-160 strips/inch
Focused Grids
Strips are angles to match the angle of the primary beam.
Need to increase mAs when using, b/c not absorbed
Grid ratio
"One of the most important factor when buying."
Ratio=height of strip:distance between them
Most 8:1/10:1
Advantages of higher grid ratio
↑ grid ratio=↑image quality
Removes more scatter
Disadvantages of higher grid ratio
↑grid ratio=↑ absorption of primary beam as well.
Have to use higher mAs.
Much more expensive.
Bucky tray
Device in tables that shakes the grid during exposure.
↑ image quality, by blurring gridlines
Types of grid cutoff artifacts
Lateral decentering
Angled
Upside-down
Cause underexposure of film
Lateral decentering
Most common cutoff
Focused Grid is not centered, so angle of strips doesn't match angle of beam.
Causes general underexposure, with apparent gridlines
Angled grid artifact
Caused by grid being tilted, relative to beam/film.
Common in Large animal.
Severe underexposure, ↑gridlines seen
Upside-down grid artifact
caused by=== upside-down grid
completely absorbs beam, except in very center
X-ray film emulsion
A gelatin mixture with silver halide crystals
1 layer in ultrasound
both sides coated in diagnostics
Conversion of silver halide to image
Crystals absorb energy (x-ray or light), release photoelectrons, which are caught by silver ions-converted to metallic silver during development
Function of intensifying screens
intensify x-rays that hit it, allowing for lower radiation use.
Actually responsible for most of the film exposure that occurs
Types of intensifying screens
Fast
Detail
How intensifying screens work
contain light-emitting phosphors in plastic support.
When an x-ray hit it releases a burst of light that exposes the film.
Fast screens
thick phosphor layer
larger phosphor crystals
for short exposure, lower detail, used for LA films
Detail screens
Thin phosphor layer
smaller phosphor crystals
much greater detail, but need higher mAs.
Used for head/extremity films
Intensifying screen artifacts
Screen craze
Screen dirt
Different color of screens for color sensitive film
Blue-sensitive=Calcium tungstate
Green-sensitive=Rare earth
Rare Earth screens
For Green-sensitive screens (orhto film).
far more efficient than Calcium tungstate screens=lower mAs
Screen Craze artifacts
Sharp white dots or irregular lines
superimposed over the radiograph
Caused by cracks/scratches in intensifying screen
Cassette dirt artifacts
Caused by objects on the screen.
Appear a sharp white areas on film (shaped like object)
Prevent by cleaning darkroom & screens @ least 1x/month
Cassettes
Hold film & intensifying screen.
Must be light-proof-felt strips around outside
Cassette components
Radiolucent material on top (carbon fiber/aluminum)
Lead on back-absorbs backscatter.
Foam on inside to keep film/screen together.
Artifacts of the cassette
Light leak artifacts
Film-screen artifacts
Light Leak Artifacts
Caused when light leaks in around edges of cassette.
Exposes the film, causing fuzzy black areas @ edges
Film-screen contact artifacts
Caused when film & intensifying screen aren't touching=decreased image detail
Affects of radiation on the body
Main effect is on DNA; causes damage that leads to cell death/ mutation or prevents cell reproduction
Units of Radiation
rad
gray
rad
=Radiation absorbed dose
gray
(IU)
1 gray=100 rads
Radiation dose equivalent
rad*quality factor=
based on type of radiation, & how much damage it can do
Units of radiation does equivalent
Rem-Radiation equivalent Man

sievert=Sv -(IU)
1mSv = 0.1 rem
1 rem = 10 mSv
Yearly limits of Radiation exposure
maximum of 5 rem/year
(5000 mrem)
Sources of radiation exposure
Background radiation
Man-made sources
Sources of Background radiation
Cosmic radiation
Earth's Crust
Interal exposure
Man-made sources of radiation
x-rays, MRI, tv, luminous watches, nuclear fallout