Extra oral radiography Flashcards
direction of beam - lateral
aimed at side of head
direction of beam - postero-anterior
starts posteriorly and passes anteriorly
true - angulation of beam
perpendicular to head
oblique - angulation of beam
not perpendicular to head
occipitomental
through occiput then mental region
mid sagittal plane
down middle of face
orbitomeatal line
10 degrees difference to frankfurt plane
connects outer canthus (lateral edge) of eye with centre of external acoustic meatus
cephalostat
ensures standardised positioning of equipment and patients head when taking a cephalogram
holds head at correct angle, stabilises head to prevent movement and establishes correct distance between patient , receptor and x ray source
uses ear rods and forehead support
how far should receptor be from focal spot in lateral cephalograms
1.5 - 1.8m to minimise magnification and diversion effects of beam
what piece of protective equipment is worn by the patient during a lateral cephalogram
thyroid collar - made of lead
what are the two options for making soft tissues more visible on a lateral cephalogram
using software to enhance soft tissues after exposure
placing an aluminium wedge in the filter to attenuate the area of beam exposing soft tissues
oblique lateral radiographs what are they and when would they be taken
extra oral radiograph taken from around the area of angle
provides view of posterior jaws without superimposition of contralateral side
Rarely used nowadays as OPT preferred but may be used if pt cant tolerate intra oral x rays or cant stay still for an opt
parallax
apparent change in the position of an object due to a real change in the position of the observer
Horizontal tube shift
method of radiographic localisation
uses two equivalent views e.g 2 bitewings or 2 periapicals
Vertical tube shift
method of radiographic localisation
uses two different views e.g panoramic and oblique occlusal
SLOB
same lingual, opposite buccal
if object of interest moves the same way as the x ray tubehead then it is lingual
used during radiographic localisation
ALARP
as low as reasonably practical
what should a practices quality assurance programme cover and include
staff training, risk assessments, image processing
how often should digital receptors be formally checked
at least every 3 months
what 3 checks should be carried out on digital receptors
receptor itself - is it clean , any visible damage
image uniformity - expose receptor to unattenuated x ray beam and check if image is a uniform shade of grey
image quality - take radiograph of test object and compare to what ideal image should be
what is meant by delamination in regards to digital receptors
phosphor layer begins to peel away from the edges of phosphor plated digital receptors
are scratches and cracks more common on solid state or phosphor plate receptors
phosphor plate
delamination can also occur
what colour will damage to receptors show as on digital and film radiograph images
digital - white
film - black
what is a common test object for image quality
step wedge - wooden stick with varying thickness of lead foil - must be able to differentiate clearly the different ‘steps’
what is a collimation error also known as
cone cutting error
what is fault analysis
identifying and explaining faults so they can be redeemed
