2.6 - Panoramic Radiography Flashcards
What does a panoramic radiograph show?
pts maxillary and mandibular teeth and also facial structures across a flat surface
What can panoramic radiographs also be called?
OPTs
DPT
DPR
What is the image layer or focal trough?
The focal trough is the area in which structures will appear most sharply and clearly.
its the layer in the pt that contains structures of interest that are demonstrated with sufficient resolution to make them recognisable whilst more sueprifical and deep structures are not seen
What is linear tomography?
The X-ray tube is moved in a straight line in one direction while the film moves in the opposite direction. As these shifts occur, the X-ray tube continues to emit radiation so that most structures in the part of the body under examination are blurred by motion. Only those objects lying in a plane coinciding with the pivot point of a line between the tube and the film are in focus.
Where is x-ray source in OPT machines?
On pts left
Where is image receptor in OPT machines?
ON pts right
Which way does x-ray source move in opts?
left to right
and image receptor goes from right to left
the image receptor rotates around the front of pt
What happens to objects not in the focal plane?
objects not in focal plane are projected to continually changing points on the film
What happens to objects in the focal plane?
Projected to same point fo film
Explain OPT and how they work
The image receptor moves in opposite direction to the x-ray source (in linear tomography the X-ray tube is moved in a straight line in one direction and film moves in opposite direction and as the shift occurs the X-ray tube continues to emit radiation - only objects lying in focal trough are in focus (those that coincide with the pivot point of a line between tube and film)
What happens to objects outwit pivot point?
Blurred out
What do we want focal trough/pivot point to contain?
All teeth and structures below the teeth (superficial and deep structures provided they are close)
what is layer formation a product of (3) ?
movement of x-ray source (x-ryay beam) through desired objects (teeth)
movement of image receptor through the x-ray beam
What is the impact of different distances from the rotation centre?
further from rotation centre the faster the beam has to pass around the circumference
closer to rotation centre slower speed (think of football stadium and tennis court)
What teeth are further from rotation centre?
Posterior teeth - this means that x-ray beam that passes through these teeth Is faster so image receptor must move at equivalent speed to get an accurate image
What teeth are closer to rotation centre?
Anterior teeth so the beam passes through slow and image receptor movement has to be slower to match and prevent distortion
What happens if speeds dont match?
Image is distorted
Which direction does beam move?
Lingual to buccal
What does distance from rotation centre to teeth affect?
How wide layer in focus is
ghost images
What is the width of layer of focal trough dependent on?
Width of x-ray beam
Distance to rotation centre - anterior teeth closer so narrowest layer in focus whereas posterior are further away so have a wider layer
Where is pts head in OPT machine?
Gantry
What must be removed before OPT?
Any metal objects
glasses
necklaces
ear nose tongue lip piercings
dentures
any mouth applainces
metal hair accessories
When pt is in OPT machine what plane do we use?
Frankfort plane horizontal or parallel to floor
What is Frankfort plane?
Upper border of external auditory meatus to lower border of orbital rim - ask pt to tuck hair behind ears
Where does the vertical narrow beam of x-ray pass?
Lingual to buccal and X-ray tube head passes behind pts head
What is the x-ray beam angulation in OPT?
angled upwards at 8 degrees due to curve of monsoon which says that buccal cusps of molar teeth are slightly high than palatal
What must the speed of beam through teeth and speed of image receptor through the beam be?
Synchronised to produce an accurate image
What do we do it pt can’t take any piercings out?
record this in notes - however if it will obstruct what we want to see then consider the point in taking radiograph
What should vertical canine line shine on?
Upper canine - if not then we have to compensate using adjustment button - if line is infront of canine press this button or if behind then press that button
What are some limitations of OPTs?
Pts occlusion
Long exposure time
Big shoulders
Positioning difficulties
Young kids, elderly, obese
Why may pts occlusion affect OPT?
Pt must be able to bite upper and lower teeth edge to edge
for pts with class 1 div 1 the upper incisors are proclined so we must decide if we want uppers or lowers in
for class3 lowers infrotn uppers so pt can’t get in right position
What can we do if we aren’t sure if pt will fit in OPT machine?
Can do a dummy run with no x-rays to check
What groups of pts may find OPTs difficult?
Young kids
Elderly
Obese - shoulder width
Special needs pts
Those with spinal problems who can’t get head straight
How long is exposure time of OPT?
Can be up to 16 seconds - hard for those with sensory problems, those who can’t stand still, those in pain, nervous pts
What can we do if movement occurs?
Can stop exposure but if mid way then we keep it going
What is a sign of movement in OPTS?
wavy border of lower mandible
What must be synchronised to produce an accurate image?
speed of beam through teeth and image receptor through beam
How is speed of beam through teeth and image receptor through beam synchronised?
the machine used canine to canine guidance and line must be on upper canine and this means machine is where it expects it to be - if this is not the case then the image is distorted
what happens if pts canine is behind canine guidance light?
This means that the pt is closer to x-ray source than the machine expects so the speed of the beam is slower through teeth as its closer to the rotation centre and as a result the image receptor will move too fast and the image will be magnified horizontally
Why may the OPT be magnified horizontally?
This can happen if pts canine is behind canine guidance and as a result the x-ray beam is closer to rotation centre and will move too fast (if its closer to rotation centre it has to move slower to compensate)
What happens if pts canine is infront of canine guidance?
This means that x-ray source if further from centre of rotation and as a result the image receptor moves too slow so the image of the teeth is reduced horizontally (to compensate the speed of beam should be faster)
Why may anterior teeth be distorted?
If not in focal trough - this can happen if we are too far from receptor (in front of canine guidance) and as a result the beam moves through slower and receptor too fast so there is magnification horizontally
or it can happen if we are too close to receptor (behind canine guidance) and x-ray beam moves too fast and receptor too slow so we have a reduced image horizontally
What are ghost images?
Second image of something in the wrong place often caused by earrings, metal restos, anatomical features such as ramus, soft tissue calcifications
Where are ghost images placed?
Higher up due to negative vertical beam angulation of 8 degrees and are horizontally magnified
Where does X-ray tube start position direct the beam at?
Posteriorly towards opposite TMJ region and the tube moves around the pts head
When a premolar region image is created where is the beam coming from?
More posterior point on opposite side
Why can a ghost image of earring be created?
This is beach x-ray beam starts in the direction and produces real image and then when it reaches premolar region it goes through earring again causing ghost image
When are OPTs used?
to check dental development
to check for developmental and acquired anomalies
to check for caries, pulpal and perio disease
pathological jaw lesions
surgery
trauma
How do we reduce dose of OPTs?
Collimation
rare earth sirens
