7. Radiology as an Imaging Science Flashcards
Emission and propagation of energy through space or through a material in the form of waves.
Radiation
Classification of Radiation
- Ionizing Radiation
- Non-ionizing Radiation
The process of removing an electron from atom.
Ionization
Types of Ionizing Radiation
- Electromagnetic Radiation
- Particulate Radiation
The transport of energy through space as a combination of electric and magnetic fields.
Electromagnetic Radiation
The magnetic disturbance propagated in space in combination of electric and magnetic fields.
Electromagnetic Radiation
Travels within the speed of light (c)
Electromagnetic Radiation
The range of wavelengths or frequencies over which electromagnetic radiation extends.
Electromagnetic Spectrum
A kind of radiation which consists of minute bits of matter travelling in space with sufficient kinetic energy.
Particulate Radiation
Types of Particulate Radiation
- Alpha Particles
- Beta Particles
Helium nuclei
Alpha Particles
Emitted from heavy elements
Alpha Particles
Travels approximately 1/20 the speed of light
Alpha Particles
8000 times heavier that electron
Alpha Particles
Penetrating power or range is limited
Alpha Particles
Average kinetic energy is 4 to 7 MeV
Alpha Particles
Ionization rate is 40,000 atoms/cm of air travelled
Alpha Particles
1 unit of negative charge
Beta Particles
Ionization rate is several hundred ion pairs per centimeter
Beta Particles
Travels almost the speed of light
Beta Particles
Sources of Ionizing Radiation
- Natural or Environmental (background)
- Man-Made (artificial)
Exposure to radiation originating from any source
Irradiation
Types of irradiation
- External irradiation
- Internal irradiation
Undesired presence of radioactive materials on any substance in concentration greater than those which occur naturally so as to cause a technical inconvenience or a radiation hazard caused by spillage or breakage.
Contamination
Modes of Human Exposure to Radiation
Contamination, Irradiation
Classification of Human Exposure
- Background radiation exposure
- Medical exposure
- Occupational exposure
- Exposure of the members of the general public
Properties of X-radiation
- X-ray photons cannot be focused by a lens
- X-rays travel in straight lines and diverge from the point of origin
- X-rays cannot be deflected by mirrors or other devices.
- X-rays travel at the speed of light
- X-rays are heterogeneous and polyenergetic.
- X-rays can ionize gas.
- X-rays can cause changes in the sensitive emulsion of the photographic film.
- When x-rays strike certain substances, visible light is emitted.
- When x-rays interact with matter, secondary radiation and scatter radiation are produced.
- X-rays can cause biological changes.
A device that converts electrical energy into electromagnetic energy
X-ray Machine
3 basic parts of X-ray machine
- High voltage generator
- Operating console/ Control Panel
- X-ray tube
Provide electrical power to the x-ray tube.
High Voltage Generator
Allows the Radiographer or Radiologic Technologist to adjust the factors needed to produce x-rays.
Operating Console/ Control Panel
Refers to the total number of x-ray photons in a beam.
Beam Quantity
Controlled by mAs.
Beam Quantity
Affected by mAs, kVp, distance, filtration
Beam Quantity
Refers to the penetrating power of the x-ray beam.
Beam Quality
Controlled by kVp.
Beam Quality
Hard beams and soft beams.
Beam Quality
Affected by kVp and filtation.
Beam Quality
A device for generating x-rays by accelerating electrons to a high energy by an electrostatic field and making them strike a metal target either in a tube containing a low-pressure gas or, as in modern tubes, in a high vacuum x-ray tube.
X-ray Tube
2 Main Parts of the X-ray Tube
- Cathode (negative side)
- Anode (positive side)
Cathode (negative side) parts
- Filament
- Focusing Cup
Anode (positive side) parts
- Target
- Rotor
- Stator
The process of releasing electrons through the use of heat.
Thermionic Emission
A device that detects radiation in order to form an image.
Image – Receptor
Records the image based on the pattern of transmitted x-rays and light produced
X-ray Film
Rigid, light-tight container that holds the screens and film in close contact.
Cassette
Cassette sizes
- 8x10 inches (20x25 cm)
- 10x12 inches
- 11x14 inches
- 14x14 inches
- 14x17 inches (35x43 cm)
Digital Radiography
- Computed Radiography (CR)
- Direct Digital Radiogaphy (DR)
Photostimulable phoshor
Computed Radiography (CR)
Flat panel detector that contains an electronic array
Direct Digital Radiogaphy (DR)
Charged-coupled devices (CCD)
Direct Digital Radiogaphy (DR)
Used in electronic process to convert light to a digital signal
Direct Digital Radiogaphy (DR)
Film Construction parts
- Outside layer
- Emulsion layer
- Base
supercoat
Outside layer
- the heart of the film
- 3 to 5 micron
- Silver Halide Crystals
Emulsion layer
- Foundation of the radiographic film
- 150 to 300 micrometer
- polyester
Base
Resistant to warping from age
Polyester
Stronger than cellulose triacetate
Polyester
Easier transport through automatic processors
Polyester
Dimensional stability is superior
Polyester
Thinner than triacetate bases but are just as strong
Polyester
Blue tint dye is added
Polyester
Maintains its size and shape during use and processing so that it does not contribute to image distortion.
Dimensional Stability
History of Radiographic Film Base
- Glass Plate
- Cellulose Nitrate
- Cellulose triacetate
- Polyester
- Dimensional Stability
Film Storage and Handling
-Storage
-Temperature no greater than 68 to 70 degrees F.
-Humidity from 40% to 60%.
-Protected from the following:
Radiation, Fumes, Outdating, Light
Unwanted densities found in the radiograph.
Artifacts
Different Types of Film
- Nonscreen film
- Copy film or duplicating film
- Film badge
- Dental film
- Bite-wing film
- Spot film
Amplify the film blackening effect on the film of an x-ray exposure by the conversion of x-ray photons to light photons to which the film emulsion is sensitive.
Intensifying Screen
The emission of light by a substance when excited by any form of energy.
Luminescence
The emission of light which ceases within 10-8 seconds of the removal of the luminescent energy source.
Fluorescence
The emission of light which continues on or is delayed after the removal of the luminescent energy source.
Phosphorescence
Intensifying Screen Structures
-Supercoat
5-10 microns
Intensifying Screen Structures
-Phosphor layer
100-200 micron
Intensifying Screen Structures
-Phosphor layer
- Calcium Tungstate
- Silver Zinc Sulphide
- Barium Lead Sulfate
- Rare Earth phosphors
Intensifying Screen Structures
- Phosphor layer
- Rare Earth phosphors
- elements with atomic number from 57 to 71
- Gadolinium (GD) (Z=64), Yttrium (Y)(Z=39), and Lanthanum (La)(Z = 57)
Intensifying Screen Structures
-Substratum layer
10-20 micron
Intensifying Screen Structures
-Substratum layer
- Reflective layer
- Absorptive layer
Intensifying Screen Structures
-Base layer
200-400 micron
Contains only the imaging plate (IP)
Computed Radiography Image Receptor (Cassette-Based System)
Key element is phosphor layer
Computed Radiography Image Receptor (Cassette-Based System)
Barium fluorohalide crystals coated with europium
Phosphor layer
Uses a flat panel direct capture detector array that absorbs radiation and converts the energy into electrical signals.
Direct Digital Radiography Image Receptor (Cassetteless System)
is defined by the International Atomic Energy
Agency (IAEA) as “The protection of people from harmful effects of exposure to ionizing radiation, and the means for achieving this”.
Radiation protection, also known as radiological protection
Radiation Agencies
- IAEA
- ICRP
- ICRU
IAEA
International Atomic Energy Agency
ICRP
International Commission on Radiological Protection
ICRU
International Commission on Radiation Units and Measurements
where radiological protection can be planned in advance, before exposures occur, and where the magnitude and extent of the exposures can be reasonably predicted.
Planned exposure
unexpected situations that may require urgent protective actions
Emergency exposure
being those that already exist when a decision on control has to be taken
Existing exposure
Exposure Situation
- Planned exposure
- Emergency exposure
- Existing exposure
No unnecessary use of radiation is permitted, which means that the advantages must outweigh the disadvantages.
Justification
Each individual must be protected against risks that are too great, through the application of
individual radiation dose limits.
Limitation
It means “the likelihood of incurring exposures, the number of people exposed, and the magnitude of their individual doses” should all be kept as Low As Reasonably Achievable
Optimization
This process is intended for application to those situations that have been deemed to be justified.
Optimization
It takes into account economic and societal factors.
Optimization
known as ALARA or ALARP
as Low As Reasonably Achievable
Reducing the time of an exposure reduces the effective dose proportionally.
Time
An example of reducing radiation doses by reducing the time of exposures might be improving operator training to reduce the time they take to handle a radioactive source.
Time
Increasing distance reduces dose due to the inverse square law. It can be as simple
as handling a source with forceps rather than fingers.
Distance
Sources of radiation can be shielded with solid or liquid material, which absorbs the energy
of the radiation.
Shielding
used for absorbing material placed around a nuclear reactor, or other source of radiation, to reduce the radiation to a level safe for humans.
Biological Shield
Three Cardinal Principles in Radiation Protection
- Time
- Distance
- Shielding
