Panoramic Radiography Flashcards
(36 cards)
What is the panoramic radiograph designed to provide?
OPT, DPT
designed to provide a clear view of the entire maxillomandibular region
What is superimposition?
Radiographs produced by passing X-ray beam through everything between X-ray source & receptor
All of these structures will be overlaid on the 2D image, potentially obscuring each other
Why is superimposition less with intra-oral radiographs?
Less of an issue with intra-oral radiographs as X-ray source & receptor can both be placed close to area of interest (therefore fewer structures captured)
What is tomography?
Tomography developed to allow “slices” of the subject to be viewed separately
solves superimposition
What are the two types of tomography in medical imaging?
- Conventional: one slice
* Mostly obsolete in medicine except for panoramic radiographs - Computed: multiple slices
What is panoramic radiography a type of?
Form of conventional tomography which was developed to capture a curved slice aligned with the “horseshoe” shape of the jaws
Where does patient, x-ray and receptor stand?
Patient stands still in middle of machine
Controlled rotation of X-ray source & receptor around head during exposure
* Both remain opposite each other but point of rotation constantly shifts
* X-ray source remains primarily behind patient
* Receptor remains primarily in front of patient
How is the area of interest exposed?
The area of interest is exposed sequentially from one side to the other over an extended time period (e.g. 14 seconds)
* This is in contrast to intra-oral radiographs for which the area of interest is exposed uniformly in a split second (e.g. 0.2 seconds)
What type of tomography does panoramic use?
modified linear tomography
What is linear tomography?
Linear tomography captures a single, flat slice by moving the X-ray source & receptor past the area of interest during the exposure
How does slice formation occur?
X-ray source moves in one direction while receptor moves in opposite direction
Structures in a “focal” slice remain projected onto same point of receptor
Structures outside this slice are continually projected onto different points of receptor
How will structures in the focal slice and structures outside the focal slice appear?
what is this called?
Structures in the “focal” slice will appear clearly distinguishable on image (focal trough)
Structures outside this slice will appear faint & spread out across image
* The further out, the worse the effect
How does the focal trough appear?
Trough is essentially a thin band where images appear adequately sharp
No defined boundaries
* Sharpness continually decreases as you move further away (buccally or lingually) until objects eventually become imperceptible
Focal trough is thinner in the incisor region
* Related to the speed of rotation at this point
* One reason for why it’s not uncommon for incisors to appear blurry
Which teeth may be far enough out of the focal trough so as to appear missing?
ectopic teeth
What is the aim of a orthogonal program?
aims to provide an optimal view of the dentition
a clearer, full view of structures without distortion
What is an orthogonal program?
X-ray beam angulation changed to be more orthogonal (i.e. closer to 90°) to the teeth
What are the disadvantages and advantages of orthogonal program?
Advantages
* Reduces overlap of the teeth to aid assessment of approximal caries
* Particularly improves view of premolars (where dental arch curvature can be pronounced)
* Improves angulation to more accurately represent interdental periodontal bone levels
Disadvantage
* Distorts rest of skeleton to varying degrees (e.g. maxillary sinuses, mandibular rami)
* Typically a narrower field of view so may miss condyles at edge of image
Where are orthogonal programs suitable?
Suitable for cases requiring only caries &/or periodontal bone loss assessment
Within the focal trough, how much is the image magnified?
25%
Magnification of structure lingual vs buccal to the focal trough?
- Structures lingual to the focal trough are magnified more
- Structures buccal to the focal trough are magnified less
Due to distortion, what do teeth positioned buccal vs lingual to the focal trough appear?
Teeth positioned buccal to the focal trough appear narrower
Teeth positioned lingual to the focal trough appear broader
Why are structures within the focal trough not distorted?
Structures within the focal trough are not distorted since the degree of horizontal magnification matches that vertically
Why are teeth wider if lingual and narrower if buccal?
Relates to how close they are to the rotating X-ray source
Remember that the beam sweeps from one side of the jaws to the other but the X-ray source is always lingual to the focal trough
What is vertical projection?
- The x-ray beam is not horizontal to the ground, it is tilted up slightly up, 8 degrees, as it passes from the back of the patient’s head to the front.
- This means structures positioned closer to the x-ray source will appear further up on the image.
