Radiology Board Review #1 Theory before anatomy Flashcards
Radiation Discovery: Who and what year?
Wilhelm Conrad Roentgen, 1895
*X-ray: unknown nature
*Discovered when experimenting with a cathode ray tube
*1st dental radiograph took in 1896
—Dr Otto Walkhoff, a German scientist, is credited with creating the first dental radiograph in 1896
Radiation
Radiation
*Emission & propagation of energy through space
Particulate Radiation
*Tiny particles of matter that posses mass & travel in straight lines at high speeds
*Electrons, bata particles, cathode rays, protons, alpha particles, neutrons
Electromagnetic Radiation
*Propagation of wave-like energy (w/out mass) through space of matter
*X-rays, cosmic rays, UV rays, visible light, infrared light, radar waves, microwaves, radio waves
*Vary in energy
*Ionizing vs non-ionizing
*Believed to move through space as both a particle (photon) and a wave
X-rays:
Shorter wavelengths: resulting from tungsten target being hit with accelerated e- in a vacuum
Higher frequencies
Wave concept:
Velocity:
speed of a wave = speed of light
Wavelength: distance between one crest of one wave and the crest of the next / distance in a periodic wave between 2 points of corresponding phrases
*Determines the energy and penetrating power
Shorter wavelength, higher the energy, more penetrating (harder) the beam
Frequency: # wavelengths that pass a given point in a certain amount of time / # of crests that pass per unit of time
Electromagnetic Radiation Wave Theory:
*How radiation propagated in the form of waves
*Useful when considering radiation in bulk when millions of quanta are being examined
Electromagnetic Radiation Quantum Theory:
Electromagnetic energy described ad bundles of energy called photons
Successful in correlating experimental data
*interaction of radiation with atoms
*Photoelectric effect
*Production of x-rays
Ionization
Most atoms are neutral
*# protons = # electrons
* Ion: atom gains or loses an electron
* Atoms lose an electron, an ion pair results
- Proton = (+)
- Electron = (-)
Ionizing Radiation:
radiation that is capable of producing ions
Photon:
*Elementary particle responsible for electromagnetic phenomena
*Carrier of electromagnetic radiation of all wavelengths
( gamma, x-ray, UV, visible , infrared, microwave, radio)
*Differs from electron & quark in that it has zero rest mass
*Travels in a vacuum & at the speed of light
*has both wave and particle properties
primary Radiation:
X-ray beam that exits the tubehead
Secondary Radiation:
X-radiation that is created when the primary beam interacts with matter
Scatter Radiation:
*Form of secondary radiation
*X-ray that has been deflected from its path by the interaction with matter
Interaction of X-radiation:
- X-ray can pass through the patient
- X-ray can be completely absorbed by patient
- X-ray can be scattered
- X-ray can be transmitted
Light can have 4 fates when hits tissue:
- Absorbed
Primary & beneficial effect of laser energy - Reflected
Beam redirecting itself off the surface, no effect on tissue.
Ex: caries-detecting laser - Scattered
May harm surrounding structures - Transmitted
May harm surrounding structures
Laser energy directly through tissues
Bremsstrahlung Radiation:
*Produced by sudden slowing or stopping of e- towards a target
*Primary source of x-rays
*Negatively charged e- directed towards a (+) charged source ——>loss of velocity occurs
*Generate continuous spectrum of photons
Characteristic Radiation:
*Only a minor source of radiation
*e- from filament displaces an e- from a shell of tungsten target atom - atom ionizes
Properties of X-Rays
*Characteristics: invisible, no mass, no weight
*Travel: in a straight line, at the speed of light
*Wavelengths:
- Have shorter wavelengths, high frequency
- Hard x-rays: short, high penetration
- Soft x-rays: longer less penetrating, more likely to be absorbed into the tissues
*Penetration: pass through matter or absorbed by matter, depending on atomic structure of matter
*Produces: an image on photographic film
*Causes: Ionization
*Distance: lose intensity with distance
Image Characteristics
Detail / Resolution / Definition:
*Over sharpness of image
*Called “radiographic definition”
*Relates to distinct and sharp demarcation of image elements
*Focal spot size: smaller = sharper image
*Film composition: smaller silver halide crystals = sharper image
*Movement of film or patient during exposure = less sharp image
*Influenced by: PID length, type of films, use of intensifying screens
Image Characteristics
Penumbra (“fuzziness or un-sharpness”):
- Source of radiation large
*Small focal spot keep penumbra small
*Large focal spot keep penumbra go up / bigger - Source to object distance
*Long SOD will go down penumbra(magnification), short SOD will go up penumbra(magnification) - Object to film distance
*Small object-to-film distance go down penumbra(magnification)
*Large object-to-film-distance will go up un-sharpness
Image Characteristics
Sharpest image with least distortion:
- Small focal spot
- Short object-to-film-distance
- Large targe(source)-to-film-distance
- Film and tooth parallel
- Beam perpendicular to film
Image Characteristics
Density:
*Overall Darkness or lightness
*More photons = more density
*influenced by: film type, processing, exposure time. mA(milli amperage) settings, PID length, kVp setting, source to object distance
Image Characteristics
Contrast:
*Variations of gray and between white and black
*How sharply dark and light areas are separated
*Influenced by: patient size, film type, processing, film storage, Mainly kVp setting
dental x-ray PID:
PID: positioning indicator device
Where the x-ray beam exposes the receptor. The x-ray head and the PID are lead lined to contain the x-ray and prevent unnecessary radiation exposure to the patient and the operator.
The PID is also called a cone.
Dental radiology—-KVP:
kVp (kilovoltage) control —– regulates the high voltage electrical circuit by adjusting the potential difference between the electrodes.
Altering the kilovoltage setting influences the quality or penetration of the x-rays produced and image contrast or differences in density.
Image Characteristics
High contrast / short scale:
*Few shades of gray, mostly black and white
*High visual contrast
*Produced by low kVp settings
*Less than 75kVp
Image Characteristics
Low contrast / Long Scale:
*Many shades of gray
*Low visual contrast
*Produced by high kVp
*Settings higher than 80kVp
Image Characteristics
Radiolucent:
*Portion of a processed radiograph that is dark or black
*Things that permit the passage of x-rays
*Air space, soft tissue
Image Characteristics
Radiopaque:
*Portion of a processed radiograph that is light or white
*Structures that absorb x-rays
*Enamel, dentin, bone, metals
Image Characteristics
Magnification:
*Image appears larger than the actual size of the object it represents
*Decrease object-film distance decrease magnification(tooth close to film)
*Increase target-to-film distance decrease magnification (use a longer PID or cone)
Image Characteristics
Distortion:
*Variation in the true size and shape of the object being radiographed
*May be unequal magnification of different parts of the same object
*Results from improper film alignment or angulation of the x-ray beam
*To minimize distortion:
1. Object and film must be parallel
2. X-ray beam must be directed perpendicular to the tooth and film
Attenuation:
Process where radiation loses power as it travels through matter. (Removal of x-ray photons)
* As the energy of radiation to up^, the # of photons passing through matter go up^
* As density, atomic #, electrons per gram of material go up^, the # of photons passing through the matter go down
Elongation:
*Central ray not perpendicular to object
*Object and film not parallel
*Insufficient vertical angulation
Foreshortening:
*Central ray not perpendicular to films
*Object and film not parallel
*Excessive vertical angulation
