CDS Radiology Flashcards
Skull radiographs
Group of radiographs used primarily for assessing maxillofacial trauma (face and jaws)
Sometimes used to assess diseases of the skull but quite limited in giving clear images of anatomy so most are supplanted with CT
Main types of skull radiograph
Occipitomental
Postero-anterior mandible
Reverse Towne’s
True lateral skull (v similar to lateral cephalogram except positioning not standardised with a cephalostat)
Difference between a lateral cephalogram and a true lateral skull radiograph
In true lateral skull the patient position is not standardised with a cephalostat
Main use of skull radiographs
Assessing skull and jaw for trauma
Primary use of occipitomental radiograph
Fractures of the midface
Primary use of postero-anterior mandible radiographs
Primarily for fractures of posterior mandible (excluding condyles)
Primary use of reverse Towne’s radiographs
Primarily for fractures of the mandibular condyles
What is the difference between occipitomental, postero-anterior mandible and reverse townes?
Fairly similar structures shown with slightly different angulations, meaning some structures are shown more clearly, and others obscured by anatomy getting in the way
How do you choose a type of skull radiograph?
Depending on what you are trying to look for
Occipitomental - midface
Postero-anterior mandible - posterior mandible (except condyles)
Reverse Townes - condyles
Skull Xray machine
Typically a specialised skull unit
Can be positioned to capture from different angles without pt having to move
Skull Xray receptor
Digital and large enough to capture relevant areas such as the entire head including jaws
Why is it so valuable that the skull Xray machine is flexible to different patient positions?
Pt can be erect or supine
Pt may be unconscious from head trauma
Pt may be drunk
Pt may have had a spinal injury
Pt position for occipitomental radiograph
Face against the receptor with nose and chin touching it, keeping a specific angle
Xray beam from behind through the back of the head, through the face and to the receptor
Machine can also be rotated to recreate this position lying down if necessary
Why is patient positioning important in skull radiographs?
Anatomy would otherwise be distorted or obscured and we will not get the information we need
Frankfort plane
Inferior border of the orbit to the superior margin of the external auditory meatus
Orbitomeatal line
Outer canthus of the eye to the centre of the external auditory meatus
Use of frankfort plane
Panoramic radiographs and lateral cephalograms
When is orbitomeatal line used?
Patient positioning for most skull radiographs
What is this patient positioned for?
Occipitomental radiograph
Name A B C
A - Frankfort horizontal plane
B - Orbitomeatal line
C - Ala-tragus line
What is the most common radiograph used in facial trauma imaging?
Occipitomental
Middle third of the face
Top of orbit to maxillary teeth
What must we try to avoid when taking occipitomental radiograph for middle third facial trauma?
Superimposition of the skull base
Why are occipitomental radiographs often taken in pairs?
They can be taken at different angles (0, 10, 20, 30, 40 degrees)
Typically use two angles that aren’t too similar (e.g. 10 and 40) to view the bones at 2 different angles increasing the chance of spotting a fracture
Le Fort
Common fracture pattern when theres major trauma to the midface
Types of middle third fractures
Le fort I, II and III
Zygomatic complex (including arch)
Naso-ethmoidal comples
Orbital blow out
Orbital blow out fractures
Pressure in the eye due to a punch or elbow or similar blow, causes the orbital contents to fracture the floor or one of the walls of the orbit
Xray beam position for a 0 degree occipitomental radiograph
Perpendicular to the Xray receptor
Centred through occiput
Xray beam position for an 30 degree occipitomental radiograph
30 degrees above a perpendicular line to the xray receptor
Centred through lower border of the orbit
What is the main difference when changing the angulation for an occipitomental radiograph?
Higher angulation moves the skull base slightly lower
Why is it important to assess the zygomatic arch after trauma?
Quite exposed
Multiple areas susceptible to fracture
Occipitomental radiographs to view mandible
Unsuitable
Mandible is not seen clearly on OM radiographs
Why are Postero-anterior mandible radiographs unsuitable for viewing facial skeleton?
Superimposition of the base of the skull and nasal bones
Indications for poster-anterior mandible radiographs
Lesions (to note medio-lateral expansion) and fractures involving
- Posterior third of body of mandible
- Angles
- Rami
- Low condylar necks
Mandibular hypoplasia/hyperplasia
Maxillofacial deformities
Patient position for postero-anterior mandible radiograph
Face towards receptor
Head tipped forward so that orbitomeatal line is perpendicular to the receptor (parallel to floor if pt standing)
Forehead nose position
Xray beam perpendicular to receptor and centred through cervical spine at level of rami
Why is the xray beam projected from posterior in skull radiographs?
Reduced magnification of the face as it is closer to the receptor so there is less room for the beam to diverge
Not much at the back of the head that is sensitive to radiation so reduced effective dose to radiosensitive tissues such as lens of the eye due to attenuation by the back of the skull
What is the patient positioned for 1 and 2?
1 - OM radiograph 0 degrees
2 - OM radiograph 30 degrees
Occipitomental radiograph 0-10 degree angulation
Occipitomental radiograph 30-40 degree angulation
Least common used skull radiograph
Reverse Townes
What type of radiograph is this?
Postero-anterior mandible radiograph
When is a reverse townes radiograph taken?
When fracture of condylar heads or necks is suspected or maybe abnormality such as hypoplasia or hyperplasia of the condyles
What is the main difference between postero-anterior mandible and reverse townes radiographs?
Reverse townes the mouth is open
Pt position for reverse townes radiograph
Face towards receptor
Head tipped forward so that orbitomeatal line is perpendicular to receptor (& parallel to floor if pt standing)
Forehead nose position
Mouth open
Xray beam 30 degrees below perpendicular to receptor and centred through the condyles
Why is mouth open for reverse townes radiographs?
To move the condylar heads out of the glenoid fossae
Why is the xray beam angled upwards for reverse townes radiographs?
For more easy visualisation of the condyles and less superimposition of the temporal bones
A
Coronal suture
B
Frontal bone
C
Greater wing of sphenoid bone
D
Nasal bone
D
Nasal bone
D
Nasal bone
E
Zygomatic bone
K
Mastoid process
F
Maxilla
G
Mandible
H
Mental foramen
I
Zygomatico-temporal suture
J
Squamous temporal bone
M
Occipital bone
N
Lambdoid suture
O
Parietal bone
L
External auditory meatus
A
Mastoid air cells
B
Lambdoid suture
C
Odontoid process/dens
D
C1 atlas
E
C2 atlas
F
Pituitary fossa/sella turcica
G
Sphenoid sinus
H
Orbit
I
Maxillary sinus
J
Pterygo-mandibular fissure
A
Fronto-nasal suture
B
Superior orbital fissure
C
Inferior orbital fissue
D
Inferior concha/turbinate bone
E
Median maxillary suture
F
Mental foramen
G
Frontal bone
H
Coronal suture
I
Supra-orbital foramen
J
Infra-orbital foramen
K
Zygomatic bone
L
Ramus
A
Maxillary sinus
B
Ramus
C
Inferior concha/turbinate bone
D
Frontal sinus
E
Ethmoid air cells
A
Nasolacrimal duct opening
B
Infra-orbital foramen
C
Condylar head
D
Coronoid process
E
Frontal bone
F
Supra-orbital foramen
G
Zygomatic bone
H
Mastoid process
A
Crista galli
B
Foramen rotundum
C
Condylar head
D
Angle of the mandible
E
Frontal sinus
F
Orbit
G
Superior orbital fissure
H
Lateral wall of the maxillary sinus
I
Odontoid process/dens of C2
What view is this?
Occipitomental
What view is this?
PA mandible
What does PA mandible view look like?
Patient facing towards you straight on
What does occipitomental view look like?
You are looking up the patients nose
What are PA mandible radiographs used to look at?
The posterior mandible
What are occipitomental skull radiographs used to assess?
Trauma to the midface
What line is used to position a patient for a panoramic?
Frankfort plane
What line is used in patient positioning for skull radiographs?
Orbitomeatal
Orbitomeatal line
Angulations for occipitomental radiographs
0-40 degrees
What type of radiograph is the patient positioned for?
Occipitomental
What type of radiograph is the patient positioned for?
PA mandible
What type of radiograph is the patient positioned for?
Reverse Townes
Periapical radiolucency associated with 41
Small lesion likely to be periapical granuloma - infection starting in the area
21 22 ULC
Abnormal root morphology - root resorption
Dens in dente 22
Periapical radiolucency 22 well defined borders
Radiopaque area distal to 15
Well defined margins
Radiolucent margin around the radiopacity
Probably odontome
Bone loss between 11 and 12 ~30%
Calculus in cervical region of 12 and 13
Maxillary sinus and nasal cavity meet at Y of ennis visible
Radiolucency mesial to 14 - vertical bone loss extending to the apex
What is the Y of Ennis?
Not a true anatomical landmark but seen only on radiographs due to superimposition of the floor of the nasal cavity (straight radiopaque line) and the border of the maxillary sinus (curved radiopaque line)
What is this anatomical landmark called, and what is it caused by?
Y of Ennis
Caused by the superimposition of the inferior border of the nasal cavity on the medial border of the maxillary sinus
Large radiolucent lesion spanning almost the entire width and heigh of the ramus of the mandible, unilocular, no resorption of the teeth, 48 being pushed down
Well defined margins
Turned out to be a tumour
Why is the orbitomeatal line used to position patients for occipitomental radiographs?
So that the skull base does not obscure your desired view
IRMER
Ionising radiation medical exposure regulations
Rank these from highest effective radiation dose to lowest
CBCT scan of all teeth
Panoramic radiograph of full dentition
Full mouth periapicals
CT scan of all teeth
CT scan of all teeth
CBCT scan of all teeth
Full mouth periapicals
Panoramic radiograph of full dentition
Why is cbct so useful?
You get all the information of a CT but with a lower dose
Very useful to look within the tissues without superimposition of other anatomy, which happens with plain radiographs.
Provisional diagnosis for the abnormal radiopacity - condensing osteitis/sclerosing osteitis
Distal root has been resorbed
Well defined radiopacity
PDL space separates the root from the radiopacity
Grossly carious tooth
What is CBCT?
Cone beam computed tomography
A form of cross-sectional imaging suitable for assessing radiodense structures, allowing you to take slices of image
Very useful to look within the tissues without superimposition of other anatomy, which happens with plain radiographs
Examples of non dental and maxillofacial radiology uses for CBCT
Temporal bone imaging
Paranasal sinus imaging
Orthopaedic imaging
Radiotherapy planning
Basic principle of CBCT
Ionising radiation
Conical/pyramidal Xray beam and square digital detector rotate around the head - no more than one full rotation
Captures many 2 dimensional images, potentially up to 200
Patient position for CBCT
Unit specific
Usually standing or sitting, rarely supine
Head position typically the same as panoramic
- Frankfort plane horizontal and midsagittal plane vertical
Benefits of CBCT over plain radiography
No superimposition
Ability to view subject from any angle
No magnification/distortion
Allows for volumetric (3D) reconstruction
Downsides of CBCT over plain radiography
Increased radiation dose to patient
Lower spatial resolution (not as sharp)
Susceptible to artefacts
Equipment more expensive - initial, running and maintenance
Images more complicated to manipulate and interpret
Requires additional training - to justify, operate and interpret
Benefits of CBCT over conventional CT
Lower radiation dose
Potential for sharper images - higher resolution
Cheaper - initial, running and maintenance
Smaller machine
Benefits of CT over CBCT
Able to differentiate soft tissues better
“cleaner” images (less fuzziness)
Larger field of view possible
Common used for CBCT in dentistry
- Clarifying relationship between impacted mandibular third molar and inferior alveolar canal prior to intervention - after plain radiograph has suggested a close relationship.
- Measuring alveolar bone dimension to help plan implant placement.
- Visualising complex root canal morphology to aid endodontic treatment.
- Investigating external root resorption next to impacted teeth - if not clear on plain radiographs.
- Assessing large cystic jaw lesions and their involvement of important anatomical structures
Common ways to view CBCT
From above or below
Sagittal view
Coronal view (straight on)
Uses for CBCT 3D volume reconstruction
May help clinician picture the extent/shape of disease
Can be an informative teaching aid for the patient
Issues with CBCT 3D volume reconstruction
It is a modified reconstruction of the data and so can create misleading images - particularly poor at showing thin bone
When are the imaging factors for CBCT set?
Before the scan starts
What will altering CBCT imaging factors impact?
The information obtained and the patient dose
Settings for imaging factors for CBCT
Should be considered on a case-by-case basis using ALARP principle
Imaging factors for CBCT
Field of view
Voxel size
Acquisition time (e.g. 10 seconds)
Field of view for CBCT
The size of the captured volume of data
Decision based on the clinical case
Increased size = increased radiation dose + increased number of tissues irradiated +increased scatter (+more to report)
Voxel size for CBCT
Image resolution
Voxel = 3D pixel
Never as small as intraoral radiograph pixels
Decision based on the clinical case
- Decreased voxel size increases radiation dose
- Decreased voxel size increases scan time (risk of pt moving)
- Decreased voxel size increases the amount of data, longer to process and more space to store
Typical range of option for voxel size for CBCT
0.4mm^3 - 0.085mm^3
When would large voxel size be used in CBCT?
When good resolution is not required, for example when needing to find out where an implant is
When would small voxel size be used for CBCT?
When good resolution is required for looking at subtle details for example when looking at root canals for endo
Imaging factor choices for CBCT for an endo case
Smallest FoV possible (unless large apical pathology)
Smaller voxel size to see the fine detail of the root canals
Imaging factor choice for CBCT for implant planning cases
FOV depends on number/position of implants
Larger voxel size - often just looking at thickness of bone, or how close the alveolar crest is to IAN canal, no fine details needed
Approximate effective doses for maxillofacial imaging
- CBCT - 13-82 uSv
- CT - 474-1160 uSv
- Panoramic 3-24 uSv
- Intraoral - 4 uSv
How does dento-alveolar CBCT radiation dose compare to a panoramic?
CBCT ~ 2-3x the dose of a panoramic radiograph
Artefacts in CBCT definition and two main types
Visualised structures on the scan that were not present in the object investigate
Most types can be avoided/reduced
Movement artefacts and streak artefacts
Movement artefact CBCT
Occurs if patient not completely still during the full exposure - affects the whole scan
Can lead to general blurriness or extra contours
Typically reduced using fixation aids - chin rest, head strap etc.
Streak artefacts in CBCT
Most notably caused by high attenuation objects
Primarily metals - e.g. amalgam, metal crowns or implants
Main issues with streak artefacts
Can prevent caries assessment adjacent to restorations
Can prevent assessment of perforations/missed canals in root canal treated teeth
Contraindications for CBCT
If plain radiographs are sufficient
Pathology requiring soft tissue visualisation such as malignancy or infection spreading in soft tissue
If high risk of debilitating artefacts - lots of metal restorations/fixed prostheses
Patient factors - pt unable to stay still e.g. Parkinsons, learning difficulties, uncooperative child, unable to fit into the machine
Can GDPs refer for CBCT?
No
Justification for CBCT
Must always be preceded by a clinical examination
CBCT can only be considered if plain radiography unable to provide sufficient information
Selection criteria - other guidance available to assist in justification from FGDP faculty of general dental practitioners
Role of GDP in CBCT
Know the common situations where CBCT can aid patient management
Know its general limitations - not as sharp, movement/streak artefacts
Know that additional training is required to use CBCT
Grossly carious UL8, distal caries UL7, periodontal bone loss, unusual appearance of sinus, retained roots with periapical radiolucencies, strange round slightly radiolucent area of bone - unusual presentation.
What is considered a “jaw lesion”
Cysts
Benign neoplasms
Cancers
Developmental abnormalities
Reactive lesions
Genetic conditions
What is the general appearance of majority of jaw lesions
Radiolucent
Importance of correct diagnosis from radiographs
Indicate need/type of further investigation
To avoid unnecessary surgery
To prompt urgent management
Three main groups of lesions on radiographs
Anatomical
Artefactual
Pathological
7 factors of lesion description from radiographs
- Site
- Size
- Shape
- Margins
- Internal structure
- Effect on adjacent anatomy
- Number
Description of site of radiographic lesion
Where is it? Alveolar bone vs basal bone
Jaws: anterior maxilla, maxillary tuberosity, mandibular body, condylar process, etc
Other: cervical spine, temporal bone, skull calvarium, etc.
Is there a notable relationship to another structure?
What is its position relative to particular structures?
e.g. inferior alveolar canal - lesions below are highly unlikely to be odontogenic
e.g. maxillary sinus floor - lesions entirely above are highly unlikely to be odontogenic
Relevance of radiographic lesions relationship to the IAN canal
Lesions below it are highly unlikely to be odontogenic
Relevance of radiographic lesions relationship to the maxillary sinus floor
Lesions entirely above are highly unlikely to be odontogenic
Description of size of radiographic lesions
very useful as some types of lesions will only grow to a certain size
Measure (or estimate) dimensions OR describe the boundaries
Eg. 50mm mesiodistally by 35mm supero-inferiorly OR Extends between teeth 34 and 38, and from the alveolar crest to the inferior cortical margin of the mandible.
“3D” imaging such as CBCT allows for more accurate determination of size.
Shape description of radiographic lesions
General
- Rounded
- Scalloped
- Irregular
“Locularity” - very important, particularly for radiolucencies, as some pathologies are ALWAYS multilocular and some other pathologies are NEVER multilocular.
- Unilocular
- Pseudolocular - appearance where only one bubble with slightly pinched in parts as if it is about to divide into locules. This can be because there are teeth pushing into it or because the bone has not expanded uniformly the whole way round.
- Multilocular - collection of bubbles
Margins of radiographic lesion description
Margins - helpful because they can often give a good idea of the nature of the lesion - e.g. benign or malignant.
Descriptions
- Well defined and OR poorly defined and
- If well defined - Corticated/non corticated - white line around the edge=corticated
- If poorly defined - blending into the adjacent normal anatomy or “moth eaten” appearance
Do corticated margins of a lesion suggest benign or malignant?
benign
Does moth eaten margins of radiolucency suggest benign or malignant?
Malignant
Internal structure of a radiolucency description
a. Entirely radiolucent
b. Radiolucent with some internal radiopacity
c. Radiopaque (homogenous or heterogenous)
Homogenous - uniformly radiopaque throughout
Description of internal radiopacities in a radiolucency
Amount - scant, multiple, dispersed, etc
Bony septae - thin/coarse, prominent/faint, straight/curved
Particular structure - enamel and dentine radiodensity
What makes jaw lesions radiolucent?
- Resorption of bone
- Decreased mineralisation of bone
- Decreased thickness of bone
- Replacement of bone with abnormal, less mineralised tissue
What makes jaw lesions radiopaque?
- Increased thickness of bone
- Osteosclerosis of bone
- Presence of abnormal tissues
- Mineralisation of normally non mineralised tissues
Pt positioning for occlusal radiographs
Ala tragus and maxillary plane parallel with floor
Angulation and position of xray beam for upper occlusal
Approx 60 downwards depending on the inclination of the upper incisors
Proclined - increase vertical angulation
Retroclined - decrease
Just above bridge of the nose 1cm above ala tragus line
Nerve passing through incisive fossa
Nasopalatine nerve
Width of incisive fossa
3-6mm
Incisive fossa appears >6mm what would you suspect?
Nasopalatine duct cyst
How is aspirational biopsy done?
Wide bore needle
5-10ml syringe
Aspirate the clear straw coloured fluid (inflammatory or developmental)
What would an aspirational biopsy of cream/white semi solid material suggest?
Orthokeratocyst
