Radiology

Question 1

which exernal reference plane of the pt should you position horizontally when setting up for a panoramic radiograph

Answer 1

frankfort horizontal plane
runs from external acoustic meatus to infraorbital rim

Question 2

if frankfort horizontal plane isnt positioned correctly, what will be the effect on the occlusal plane on the image

Answer 2

if chin is down = smiling occlusal plane
if chin is up = flat occlusal plane

Question 3

what margins is seen horizontally above roots of maxillary premolars

Answer 3

floor of maxillary sinus

Question 4

what margin/wall is seen vertically above the third molar region

Answer 4

zygomattic buttress

Question 5

benefits of digital over film radiography

Answer 5

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

Question 6

what is the benefit of using rectangular collimation

Answer 6

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

Question 7

what chemical property of lead makes it effective at absorbing x-ray photons

Answer 7

high atomic number, has a greater probability of undergoing photoelectric effect with incoming x-ray photons, absorbing efficiently

Question 8

what is the minimum distance for a dentist to stand at when radiographic exposure

Answer 8

1.8-2mm

Question 9

what does the term justification mean in context of deciding when or when not to take a dental radiograph

Answer 9

the benefits of taking the x-ray must outweigh the negative risk of radiation exposure

Question 10

what does ALARP mean

Answer 10

as low as reasonably practicable

Question 11

how are x-rays produced

Answer 11

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

Question 12

how is a ghost image produced

Answer 12

-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

Question 13

what are the size of collimators used

Answer 13

50x40mm, no more than 60mm

Question 14

how is radiation dose reduced

Answer 14

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

Question 15

what radiograph to check for retained roots

Answer 15

periapical
panoramic if poor cooperation

Question 16

what happens if the pt is too far or too close to the x-ray film/source

Answer 16

too close = increased magnification and radiation dose
too far = decreased magnification, reduced image quality, underexposure, increased scatter radiation

Question 17

indications for OPT

Answer 17

full view of dentition and surrounding structures
poorly cooperative children or cannot tolerate IO

Question 18

what does OPT radiographs show

Answer 18

fractures, evaluation of trauma, 3rd molar relationships, large lesions, retained/unerupted teeth, developmental/acquired abnormalities, TMJ evaluation

Question 19

what positioning error in an OPT results in the incisor teeth being horizontally magnified

Answer 19

chin placed too high
tiltled upwards

[flat occlusal plane also]

Question 20

what positioning error in an OPT results in the posterior teeth on one side being wider than on the other

Answer 20

head tilted/rotated in one direction

Question 21

important features that apply to all ghost images

Answer 21

magnified, blurry, superimposed on other side, higher

Question 22

what type of radiograph when examining 48, 38 is fine

Answer 22

right half panoramic

Question 23

what type of panoramic when uncooperative child

Answer 23

OPT

Question 24

describe the process of compton scatter and how it differs from the photoelectric effect

Answer 24

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.

Question 25

what metal is sued to absorb the heat generated during x-ray production

Answer 25

copper

Question 26

name metals used in x-ray production

Answer 26

tungsten
aluminium

Question 27

what is measured in grays?

Answer 27

absorbed dose

Question 28

link of radiotherapy in region to formation of ulcers

Answer 28

moderate to high dose given to overlying tissues
oral mucositis
sensitive, rubbing, traumatic ulcers