BDS4 Types of radiological views Flashcards
What are skull radiographs primarily used for?
Group of plain radiographs used primarily for assessing maxillofacial trauma - except complex cases which are assessed using CBCT
What are the main types of skull radiographs?
Occipitomental
Postero-anterior mandible
Reverse Towne’s
True lateral skull
What is the benefit of being able to position a patient standing up or lying down for skull radiographs?
Good for trauma cases where a patient may be unconscious or drunk and unable to stand up
What is the reference line used in patient positioning for most skull radiographs?
The orbitomeatal line - outer canthus of the eye to the centre of the external auditory meatus
What does an occipitomental radiograph show and what is it mainly used for?
Shows the facial skeleton, avoiding super-imposition of skull base and is mainly used for middle third facial fractures
Why are occipitomental radiographs generally taken in pairs?
Viewing the bones at 2 different angles increases the chanced of seeing a fracture
What are indications for occipitomental radiographs?
Middle-third fractures
- Zygomatic complex
- Naso-ethmoidal complex
- Orbital blow out - pressure in the eye if a wall/ floor of orbit has been broken inwards.
Coronoid process fractures
What does postero-anterior (PA) mandible radiograph show?
Posterior parts of the mandible
What are indications for PA mandible radiograph?
Lesions and fractures involving
- Posterior third of body
- Angles
- Rami
- Low condylar necks
Mandibualr hypoplasia/ hyperplasia
Maxillofacial deformities
Why is the x-ray beam projected from the posterior side in PA mandible radiographs?
Reduced magnification of face (since closer to the receptor)
- Less distortion of relevant structures
Reduced effective dose
- X-ray beam partly attenuated by back of skull before reaching face
- Lower radiation dose to radiosensitive tissues e.g. lens of eye at front of face as a result
What does the reverse townes radiograph show?
Shows the condylar heads and necks but RARELY used nowadays
Similar to PA mandible radiograph but different x-ray beam angle and MOUTH OPEN
What are the basic principles of CBCT?
Captures many 2D images which are reconstructed into a 3D image - can view “slices” of the image.
Conical X-ray beam & square digital detector rotate around the head
What are the benefits of CBCT over plain radiography?
No superimposition
Ability to view subject from any angle
No magnification/ distortion
Allows for volumetric (3D) reconstruction
What are the downsides of CBCT over plain radiography?
Increased radiation dose to the patient
Lower spatial resolution - not as sharp
Susceptible to artefacts
Equipment more expensive - initial, running & maintenance costs
Images more complicated to manipulate and interpret
Requires additional training
What are common uses for CBCT?
Clarifying relationship between impacted M3M and IA canal prior to intervention - after OPT has suggested close relationship
Measuring alveolar bone dimensions to help plan implant placement
Visualising complex root canal morphology to aid endo tx
Investigating external root resorption next to impacted teeth
Assessing large cystic jaw lesions
What are the main benefits of a CT scan over CBCT?
LARGER FIELD OF VIEW POSSIBLE
Able to differentiate soft tissues better
“cleaner” images
What is the approx. effective dose for CBCT?
13-82 uSv
What is the approx. effective dose for CT?
474-1160 uSv
What is the approx. effective dose of panoramic radiograph?
3-24 uSv
What is the approx. effective dose of intra-oral radiograph?
4 uSv
What is a movement artefact and what will be seen on the scan?
Occurs if pt. not still during full exposure - affects whole scan
Can lead to general blurriness or extra contours
What is a STREAK artefact?
Looks like streaks of light on the scan
Mostly caused by high-attenuation objects - primarily metals
What are the main issues caused by STREAK artefacts?
Can prevent caries assessment adjacent to restorations
Can prevent assessment of perforations/ missed canals in RCT teeth
What are contra-indications for CBCT?
If plain radiographs are sufficient
Pathology requiring soft tissue visualisation - malignancy, infection spreading in soft tissue
If high risk of debilitating artefacts - lots of amalgams
If patient unable to stay still e.g. Parkinson’s
