Panoramic Radiography Flashcards
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.
Why are panoramic better than periapicals?
- Can capture entire dentition in one image
- Able to image non-dental areas e.g. rami, condyles, maxillary sinuses
- Lack of intra-oral holders benefits some patients e.g. gaggers, trauma cases, young children
Why are panoramics worse than periapicals?
Worse clarity
* Lower spatial resolution
* More superimposition
* More artefacts
Longer exposure time
* Increased risk of patient movement
Higher radiation dose per image
* Approximately 5x more for a “full” panoramic radiograph
What are the main components of the panoramic machine?
- X-ray tubehead
- Receptor (usually digital)
- Control panel
- Patient-positioning apparatus
What ar the common options on the control panel?
Field size
Arch size/shape
Position of machine (e.g. height) Position of patient-positioning apparatus
X-ray tube exposure factors
* Voltage (e.g. 60-90kV)
* Amperage (e.g. 4-12mA)
Specialised use cases
* “Bitewings”, TMJ assessment, etc.
How to prepare before a OPT?
Remove metal foreign bodies from head & neck
* e.g. piercings, glasses, dentures, necklaces, hairclips
Position patient in machine
* Set machine at correct height
* Keep neck as upright as possible
* Position head using positioning apparatus
* Patient holds handles for stability
Advise patient
* Tongue to roof of mouth
* Stand still
* Do not talk or swallow
What does the bite peg do?
- Forces patient into edge-to-edge occlusion
- Positions both arches in focal trough
What do the light beam markers do?
- Horizontal line matches Frankfort plane (keeps chin level)
- Infraorbital margin→upper margin of EAM
- Vertical mid-line matches mid-sagittal plane
- Canine lines match maxillary canines
What happens if the patient is slumped?
excessive cervical spine shadow
What happens if the patient is too far forward?
into the machine
- Incisors now buccal to focal trough
- Incisors appear narrower
What happens if the patient is too far backwards?
- Incisors now lingual to focal trough
- Incisors appear wider
What happens during scan?
X-ray tube & receptor rotate part-way around head
“Full” panoramic radiograph typically takes 10-15s
What must the patient do during the scan?
- Stay still
- Press tongue up against palate
- Not talk or swallow
Is a lead apron necessary for patient?
There is no justification for the routine use of protective aprons for patients undergoing any form of dental radiography or dental CBCT imaging as the main X-ray beam should never be directed towards the abdomen. Doses to the patient or the foetus from scattered X-rays and leakage will then be negligible as will the associated risk.”
* Guidance Notes for Dental Practitioners on the Safe Use of Dental X-ray Equipment (2020
