Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

A Review on panoramic radiography:
Principles of panoramic image formation:
-

-

In rotational panoramic tomography, the image receptor and tube head
are connected – they rotate simultaneously around the patients head in
a controlled accurate movement to reproduce a curved dental arch on a
flat surface
Consists of 2 slit shaped lead collimators located at the x-ray source and
at the image receptor – limits the central ray to a narrow vertical beam
As the tube head rotates, the x-ray beam passes through diff parts of
the jaw and produces multiple images that appear as one continuous
radiographic image in the end
...


The Focal Trough:
-

Aka the image layer
= a 3D horseshoe-shaped/ curved zone (corresponds to shape of dental arches) composed largely of the
anatomic structures
The focal trough is the area in which structures will appear most sharply and clearly
Teeth and structures, which fall in front or behind the focal trough will have blurring, distortion,
magnification or other artefacts
The focal trough is narrow (3mm width) in the anterior region making positioning critical in obtaining quality
radiograph
Patients must be properly prepared and positioned with their head carefully aligned in the focal trough,
where the dental arch is positioned with a narrow zone of sharp focus
New innovation of OPG machines (2D and 3D) are now available with enhanced focal trough complementing
panoramic imaging – still have correct head orientation
...
Also most OPG units have laser guide
lights
...
Frankfurt Horizontal Plane
o Plane passing through inferior margin of left orbit and
the upper margin of each ear canal or external auditory
meatus
...
Median plane (midsagittal plane)
o Represents sagittal plane with extends from the vertex
via centre of nose to chin
...
Frontal plane (coronal plane)
o Vertical plane passing through the porion vertically ,
perpendicular to median plane
...


Frontal view diagram highlighting planes:
-

-

Focus on head orientation, make sure
neck is straight to avoid excessive
overlapping of cervical spine
...

The immobilising head supports are in
space
...


The 6 anatomical zones: Evaluating an OPG
-

-

-

-

-

Important to evaluate image bilaterally to look for asymmetry
...

Dentition (Zone 1)
o Teeth are arranged with an upward smile-like curve
o Anterior teeth should not be too large or small
o Posterior teeth evenly sized without excessive overlap
o Apices and crowns of teeth should be visible
Nose and sinus (Zone 2)
o The following are visible in zone 2:
o Shadow of hard palate is seen in maxillary area
o Soft tissue of the nose should not be visible
o Inferior nasal concha and surrounding air spaces
cavities visible
o Tongue should be in contact with the hard palate
o Nasal septum and cavity should be visible
Mandibular body (Zone 3)
o Inferior border of the mandible is smooth and continuous –
have proper proportions so no step defects (error due to
movement)
o The ghost image of the hyoid bone should not be visible
o Midline area should have proper proportions
Condyles (Zone 4)
o Left and right condyles should be centred within
the area of the zone
o Left and right condyles should be of equal size
and are on the same horizontal plane

-

-

Ramus and spine (Zone 5)
o Ramus of the mandible should be equidistant or of
similar width bilaterally – no step defects!
o Shadow of the spine may be present as long as it
does not superimpose over the ramus
o If the spine is visible the distance between the ramus
and spine should be equal to both sides
o Shadow of the ears visible on both sides
Hyoid bone (zone 6)
o Hyoid bone should appear bilaterally, the
double image with equal proportion
o Hyoid bone may touch the mandible however it
should not appear to cross it

Normal Anatomic (Panoramic) Landmarks:
-

Panoramic imaging or OPG produces a tomographic image of both the maxillary and the mandibular arches
and surrounding bones, soft tissue structures and air cavities in a single image
...


These are 15 of the normal panoramic landmarks:

-

We have 30 in total, or even more if we include air cavities
...


These slides show these landmarks separately in their category: bony anatomy, soft tissue anatomy and air spaces
...

-

Radiographic quality determines if all features are clearly visible
...
Shapes part of eye socket and opens to create nasal
cavity, provides attachment for palate
Mandible = largest strongest lowest bone of our face
...
Includes condyle , coronoid process, ramus and the body with the mental foramen and ID nerve canal
...
Right are air cavities that are very
present in OPG’s, we have ~7 of them
...
These can hinder an accurate
diagnosis and interfere with accuracy
Double image = an artefact produced by the panoramic technique and occurs when an object or anatomic
structure is between the x-ray tube and image receptor
...


Ghost image = an observed artefact inn OPG where a dense object or anatomic structure is located between
the source of x-ray and centre of rotation, resulting in a duplicate ‘ghost’ image or shadow
...

Structures often ghosted can be anatomical or non-anatomical – this radiograph shows a non-anatomical
ghost image on opposite side, this is a steel earring

-

Characteristics of ghost images:
o Image has the same general shape of original object or anatomic structure but doesn’t produce
mirror image
o Image appears on opposite side of panoramic image compared to original object
o Image always projected at higher position on the image than original object
o Image appears unsharp/blurred and magnified compared to original
o Image always reversed projected on opposite side
o Common ghost images: necklaces and earrings, cervical spine, rami of mandible and inferior border
of mandible, orthodontic appliances

Radiographic technique:
-

-

-

Equipment preparation:
o This includes the rotating component of machine (image receptor and tube head), occlusal bite block
and immobilising rods (forehead and temple support), exposure & programme settings, height of
machine and image processing software
...
Pre-programmed factors
according to patient size or single setting for children and adults
o Height of machine = adjust the height of the unit to approximate height of patient prior to patient
positioning
o Image processing software (SIDEXIS) = structures workflow of exam, image analysis and orientation
o PACS and QDoc = image transmission from site to storage and viewing
...
Items such as
headbands, hair clips, hearing aids, reading glasses must be removed prior to imaging
o Protective garment = lead-free apron “panoramic poncho” provide protection for radiosensitive
tissues in the neck
...

Patient positioning:
o Patient positioning errors are the most common type of error when performing panoramic
radiography or when tongue not placed close enough to palate
...
If sitting, sit upright
...

o Mouth position= instruct patient to place maxillary/mandibular incisors correctly on the bite block
for proper alignment of the teeth
o Mid-sagittal plane = patients head must be straight not tilted, MSP must be kept perpendicular to
floor
o Frankfort plane = this plane is kept parallel to the floor
...

o Eyes= instruct patient to close their eyes to avoid following the movement of the tube head

-

The basic steps of taking an OPG:
1
...
Set up QDoc/SIDEXIS, ensure all info is correct, fill in radiation dose etc
3
...
Put hygienic cover on bite block and open head supports, Adjust height to approx
...
Ask patient to remove any jewellery or foreign metal objects on head and neck
...
Press up and down on unit to adjust height of bite block, slightly higher than pts chin
...

7
...
For edentulous
(full or partially), positioning aids e
...
chin rest or bar, and cotton rolls available
...
Instruct patient to close eyes, press laser to initiate laser alignment lights, verify head isn’t tilted
9
...
Check midsagittal plane perpendicular to floor using mirror guide
...

10
...
Prior to exposure, check pts holding hand grips, support pts head position w gentle pressure on head
12
...
Take x-ray while keeping an eye on patient
...
In children, also tell them to keep eyes
closed or keep eye on a fixed spot infront
of them bc tendency to follow you with
their eyes & whole head
...

Patient positioning:
o Non-anatomical (artefact) shadows- these are white opacities on xray, caused by
jewellery
...
g
...

Also, hearing aids etc
...

o Head/chin tilt ‘too low’
▪ Joker smile
...


o

Head/chin tilt ‘too high’
▪ Waved shape occlusal plane
...
Blurs maxillary incisors and shortens mandibular
rami, condyles appear at edges
...


-

-

o

Head tilted or tipped to one side:
▪ TMJ’s appear uneven
...
The side with wider condyle and ramus are closer to tube head
...


Bite on occlusal bite block:
o Biting too far forward:
▪ Anterior teeth out of focus; appear
blurry, too small and narrow
...

Patient instruction
o Tongue not against the palate
▪ Where large dark shadow of air space over maxillary
teeth or roots of molars
...


▪

o

o

o

Horizontal movement (red) is a distorted UR premolar that might
be mis-interpreted as a ghost shadow or pathology
▪ Vertical movement (red oval) also shows the distortion of Upper
and lower right molars
▪ Notable step defect in lower border of mandible; inferior border
isn’t continuous
...

Double exposure:
▪ This is where multiple images of double structures and teeth
are taken and seen in one film
...

Ghost of spinal column
▪ Here, the neck is not kept erect during expsore, resulting in
shadow of spine obscuring view of teeth
▪ Correct this by reminding patient to stand straight
...

o Examine border and margins of image
o Examine borders of jaw bone (mandible)
o Examine the osseous structures of maxillofacial region (zygoma and maxillary sinuses)
o Check the internal structures (nerve canals and foramina)
o Check soft tissue structures (nasal cavity, nasal floor, airspaces)
o Save the teeth for last!



---