Radiology Flashcards
which exernal reference plane of the pt should you position horizontally when setting up for a panoramic radiograph
frankfort horizontal plane
runs from external acoustic meatus to infraorbital rim
if frankfort horizontal plane isnt positioned correctly, what will be the effect on the occlusal plane on the image
if chin is down = smiling occlusal plane
if chin is up = flat occlusal plane
what margins is seen horizontally above roots of maxillary premolars
floor of maxillary sinus
what margin/wall is seen vertically above the third molar region
zygomattic buttress
benefits of digital over film radiography
easily stored/accessed
easily shared
images can be manipulated
no need for chemical processing
images can be integrated into pt record
reduced radiation exposure
imrpoved image quality
what is the benefit of using rectangular collimation
lead diaphragm attached to end of spacer cone
crops the x-ray beam to match the size/shape of collimator
reduces surface area which is being irradiated by almost 50% and reduces collimation errors
pt exposed to less radiation
what chemical property of lead makes it effective at absorbing x-ray photons
high atomic number, has a greater probability of undergoing photoelectric effect with incoming x-ray photons, absorbing efficiently
what is the minimum distance for a dentist to stand at when radiographic exposure
1.8-2mm
what does the term justification mean in context of deciding when or when not to take a dental radiograph
the benefits of taking the x-ray must outweigh the negative risk of radiation exposure
what does ALARP mean
as low as reasonably practicable
how are x-rays produced
produced by fast moving electrons which are brought rapidly to a stop
electrons accelarated towards atoms at high speeds, on collision the kinetic energy of electrons is converted to heat and electromagnetic radiation [x-ray photons]
these x-ray photons are aimed at subject
how is a ghost image produced
-Parallax effect = pt anatomy not aligned properly with focal plane
-Scatter radiation, multiple reflections, backscatter
projected from one side to the other, blurry, magnified, higher [due to beam inclination] and transposed to other side
earings, metal restorations, hyoid bone
what are the size of collimators used
50x40mm, no more than 60mm
how is radiation dose reduced
use of rectangular collimators to reduce surface area irradiated
beam-aiming device and film holder
aluminium filter
reduced irradiated area, reduces number of scattered photons and pt dose
what radiograph to check for retained roots
periapical
panoramic if poor cooperation
what happens if the pt is too far or too close to the x-ray film/source
too close = increased magnification and radiation dose
too far = decreased magnification, reduced image quality, underexposure, increased scatter radiation
indications for OPT
full view of dentition and surrounding structures
poorly cooperative children or cannot tolerate IO
what does OPT radiographs show
fractures, evaluation of trauma, 3rd molar relationships, large lesions, retained/unerupted teeth, developmental/acquired abnormalities, TMJ evaluation
what positioning error in an OPT results in the incisor teeth being horizontally magnified
chin placed too high
tiltled upwards
[flat occlusal plane also]
what positioning error in an OPT results in the posterior teeth on one side being wider than on the other
head tilted/rotated in one direction
important features that apply to all ghost images
magnified, blurry, superimposed on other side, higher
what type of radiograph when examining 48, 38 is fine
right half panoramic
what type of panoramic when uncooperative child
OPT
describe the process of compton scatter and how it differs from the photoelectric effect
Compton scatter involves partial energy transfer from the photon to an electron, leading to a scattered photon with reduced energy and altered direction.
The photoelectric effect results in complete absorption of the photon’s energy by an electron, causing the electron to be ejected from the atom with kinetic energy.
Photoelectric – photons hit electrons, if this photon has enough energy then it will knock electron out of place
- If the photon energy is greater than the atoms binding energy, it will knock out
- More pronounced with low energy photons
Compton – photon hits an electron, there is a loss/transfer of energy and scatter of the photon with reduced energy
- More significant with high energy photons
The Compton effect involves photon-electron scattering with energy and momentum transfer, leading to a change in photon wavelength and direction, while the photoelectric effect results in the ejection of electrons from materials upon absorption of photons with sufficient energy, producing photoelectrons and ionization.
