Theme 2 - Radiology Flashcards
(48 cards)
What are the 3 focal trough samples from a conventional DPT?
1) Beam through TMJ, sinuses and nasal structures
2) Beam through dental arch
3) Beam through mandible
What is the difference in focal trough width in a DPT and a CBCT?
What effect does this have?
DPT = 3cm post, 1 cm ant
CBCT = 0.4mm
Much clearer image but much higher dose of radiation
What is the effective dose for
a) Full mouth PAs
b) DPT
a) 150 uSv
b) 15-20uSv
What has caused the following positioning problems in a DPT?
a) Occlusal plane smiling, elongation of chin and no separation of teeth?
b) Occlusal plane frowning, shortened ramus, hard to see root apices of maxillary teeth
c) Lots of vertebral column/spine on show, teeth and jaw narrowed
a) Head inclined forward (looking down)/frankfort plane tilted down
b) Head inclined to rear (looking up)/ frankfort plane backwards
c) Pt too far forwards in machine
What has caused the following positioning problems in a DPT?
a) No spine on image and magnified anterior teeth
b) Teeth magnified on one side, one sinus denser, ramus different sizes
c) Inclination of central line and unequal distance on each side between edge of image and TMJ
d) Wavy image
a) Pt has head too far back in machine
b) Rotation - magnified side is the side furthest from film
c) Lateral inclination of head ie tilting
d) Pt unable to keep still e.g. parkinsons or children
Where will a ghost image be located on a DPT?
- Opposite side from image of actual object
- Larger than image of actual object
- Projected higher on film
- Less distinct
(from mandible or metal jewellry)
How is a patient positioned for a lateral ceph?
Pt at known distance from xray source, parallel positioning of auditory meatus, ruler on nasion
What areas should be looked at when analysing a lateral ceph?
-Frontal sinuses for pathology and development
- Base of skull and pituitary fossa to asses for expansion and erosion
- Facial bones for pathology
- Upper spine for pathology and airway spaces
What may you see on a lateral ceph that would indicate acromegaly?
Frontal sinus large (frontal bossing)
Large pituitary fossa (can impact on optic chiasm)
Class 3
What bone causes challenges when facial imaging because it superimposes over the facial bone?
Petrous temporal bone
What does the undertilted occiptomental (OM) facial view show?
What does the OM 30 show?
What does the submental vertex view (SMV) show?
1) Lower orbit to look for fractures - petrous temporal bone under maxillary sinuses
2) Zygomatic arches - petrous ridge well below temporal bone
3) Zygomatic arches - taken under chin
What is the reverse townes view (occipito-frontal 30)
Xray behind pts head (reduce dose to eyes), pt keeps mouth open, radiographic baseline 90 degrees to film. Beam angled 30 degrees up.
Captures zygomatic arches and allows condylar necks to be seen
What is the occipitomental view (OM)?
Xray behind pt, pts facial bones close to image to avoid magnification, radiographic baseline at 45degrees to film, central ray through base of nose.
Good for mid third of face and orbital structures
What lines are used to analyse an OM view?
Campbell lines
1 = suprorbital
2 = zygomatic arches
3 = mastoid and upper teeth
4 = lower border of mandible
What is the PA mandible view?
Radiographic baseline 90 degrees to film, beam approaces through mandible at 90 degrees to fil.
Shows fractured condylar neck, not zygomatic arch, cervical spine tends to obscure anterior part
What is the lateral oblique mandible?
Median saggital plane at 45degrees, beam approaches from under the mandible and the side closest to film seen most clearly
How does the Y of Ennis help with localisation?
If no surrounding teeth and root remenent just below it is a 3
Doesn’t tell you where it is palatal/labially, but does tell you where it is anterior/posterior
How does parallax help localise?
2 images where xray tube moves and pick reference point.
SLOB: Same direction = lingual, opposite direction = buccal
How can foreign bodies in soft tissue be identified by a radiograph?
Taken at lower kVp (60kV rather than 70kV)
2 views at right angles needed
Use ultrasound too
What factors influence the justification for a CBCT?
- Pathology
- Competence (trained in use and interpretation)
- Consent
- Risk/benefit
- Dose of radiation
What do the following mean
a) Coronal
b) Axial
c) Sagittal
a) Through coronal suture
b) Transverse slice
c) Through saggital suture
What is the classification of CBCT units commonly used in dentistry?
Single arch 5-7cm field of view
What is the difference between CBCT/iCat and multidetector/medical CT?
- See better ST planes with MDCT but higher radiation dose
- Fan beam
What are the uses of CBCT?
- Assess L8 and ID canal relationship
- Implant planning
- Endo
- Ortho controversial as higher dose than lateral ceph
