Radiography Flashcards
What are 2 different ways of getting localisation?
- Two views at right angles to each other
2. Two views at less than 90 degrees to each other (Parallax)
What is the main indication for radiographic localisation
Endodontics - mesial shift to view obstructed multiple roots
What is parallax?
Displacement of apparent position of an object based on change of position of the point of observation
Rational: hidden objects can be seen from a different vantage point, but actual relationship of the objects hasn’t changed, only the observer’s viewpoint
What are the 2 techniques to accomplish parallax?
Horizontal Cone Shift
Vertical Cone Shift
You have an upper 1st molar with two roots. If you move the x-ray beam mesially to the right, what direction does the lingual root move?
SLOB rule: Same Lingual, Opposite Buccal
Moving to the right, lingual also moves to the right
You have an upper 1st molar with two roots. If you move the x-ray beam distally to the left, what direction does the buccal root move?
SLOB rule: Same Lingual, Opposite Buccal
Moving to the left, buccal moves opposite to the right
For a vertical cone shift there are 2 objects - one buccal and lingual superimposed on the tooth.
If the shift is done superiorly, what direction does the lingual object move on the radiograph
The Lingual object appears more superiorly
What is an alternative to Radiographic Localisation?
3D imaging using CBCT
Why might you do radiographic localisation when planning an impacted tooth extraction? What sort of localisation would you do?
PA/BW won’t tell you how far lingual/buccally placed the tooth is on a 2D image. This would be vitally important so the incision is made on the correct aspect of the dental arch.
You would do localisation 90 degrees to the PA/BW. This would be an occlusal radiograph
In the ADH, which direction does the black side of protective sleeve does the phosphor plate face?
The black side of the protective sleeve faces the beam. Otherwise Clinic 1.2 David gets very very angry. This helps in terms of digital orientation
What is the scope of practice for Dentists for OPGs
BOH + BDS
- Exposing Panoramic Images
- Recognition of Anatomical Structures
- Recognition of Normal vs Abnormal
BDS Only
- Prescribing Panoramic Images
- Diagnosis
What are the contraindications for taking an OPG?
Caries Detection
Routine Screening
Young Children
What are the indications for taking an OPG?
Bottom line - radiographs only taken when there is an expectation that the diagnostic yield will affect patient care
1. Bony Lesions 2Unerupted Tooth size and positioning 3. Grossly Neglected Mouths 4. Periodontal Bone Assessment (albeit with limitations) 5. Wisdom Teeth assessment prior to surgery 6. Orthodontic Assessment 7. Educational/Motivational Aid Mandibular Fractures 8. Antral (Maxillary Sinusitis) Disease 9. TMJ Pathology 10. Vertical Alveolar bone height / position of anatomical structures prior to implant planning 11. Full view of pathology
What charge codes need to be entered into Titanium for an OPG?
037_ORDERED: during examination
037: When it’s taken
037_VIEWED: your clinical notes as operator what is visible
037_REPORT: summary of radiologist report
Why might you opt to use an OPG over a Full Mouth Survey?
- When less sharpness is required
- Picking up all surrounding structures
- When reproduction for series records needed
- Picking up asymptomatic symptoms
What are disadvantages of OPGs?
Less Detail Superimposition Patient needs to be very still Anatomical Variation can make imaging difficult Equipment more expensive
T/F: You would use a thyroid shield for a pregnant patient when taking an OPG
False - the thyroid shield would obstruct the centre of the image. Use a collarless lead apron instead.
What safety measures are needed for operators when taking an OPG?
1) Be at least 2m away from the x-ray tube
2) Stand behind the lead shield barrier
T/F: A Radiation badge is required for CBCT radiography
True, they are not required for OPG or Bitewing radiographs
What is the purpose of the secondary vertical slit collimator in an OPG?
Progressive moves along the cassette during exposure so that one continuous exposure can be taken onto the film/sensor during the full rotation of the x-ray beam
What is the benefit of a Photostimulable Storage Plate (PSP) for an OPG?
Reusable plate.
It is able to be retrofitted to non-digital OPG machines.
What is the purpose the primary vertical slit collimator on an OPG?
Reduce scatter of radiation coming out of the x-ray tube
T/F: The movement arc of an OPG is elliptical
True, it has 3 centres of rotation to account for the curvature of the mandible and the desired objects of interest within the focal trough
What factors could mean that the patient is not positioned within the focal trought
- Poor Patient Positioning
2. Patient anatomy outside normal range
T/F: The medial aspect of the condyle is imaged first on the OPG
True
Would a structure lying lingual to the trough be reduced or magnified in the image?
Magnified - think finger puppets, closer to the light source appears larger on the film
Would a structure lying buccal to the trough be reduced or magnified in the image?
Reduced- think finger puppets, closer to the film appears smaller on the film
How do structures outside the focal trough appear on the OPG?
Poorly Defined
Magnified or Narrowed
Distorted in shape
Superimposed
How do you ensure good patient position?
Machine Head Position
Chin Rest: correct height
Bite-Block: place incisors in the midline
Forehead Rest, Lateral Head supports/Clamps: ensure no movement
Machine laser guide lights
How would an OPG appear if the patient is positioned too far forward
Image reduced on horizontal plane
Anterior Teeth Narrower
Spine visible
How would an OPG appear if the patient is positioned too far backwards
Image increased in horizontal plane
Wide Anterior Teeth
How would you ensure correct proportions of anteriors for Class II/II occlusion patients on an OPG?
Class II: Tell the patient to protrude mandible
Class III: Tell the patient to retrude mandible
How would an OPG appear if the patient has rotated their head?
Horizontal distortion on both sides:
Side closer to tube: teeth wider, fuzzier
Side closer further from tube: teeth narrower, clearer
What is a secondary/ghost image on an OPG?
An artefact that exists in front of the centre of rotation (ex earrings)
As it is closer to the tube, it will appear large, blurred, higher and on the opposite side.
What is a primary image on an OPG?
Occurs when structure lies between centre of rotation and film
How do we avoid unnecessary dark images on the OPG?
Patient needs to close lips and raise tongue to the roof of their mouth
What air spaces are possibly visible on an OPG?
Naso-Pharyngeal Space Oro-Pharyngeal Space Palatoglossal Space Nasal Cavities Maxillary Sinuses Mastoid Air Cells Open Lips
What soft tissues are possibly visible on an OPG?
Ear Lobes Soft Palate Tongue Nose Lips
T/F: The rotational speed of an OPG is constant
False - the tube has variable speed depending on the distance to the source
What are the steps to positioning the patient for an OPG?
- Raise chin rest to max height
- Get patient to enter the unit
- Adjust unit height
- Tell patient to
- Stand Straight
- Grip lower handles
- Rest Chin on Chin Rest
- Position feet slightly forward
- Feet slightly apart for stability
- Relax Shoulders - Turn on mid-sagittal / horizontal positioning beams: adjust accordingly, get patient to look straight forward
- Bite on bite block and adjust for class II/III occlusion
- Immobilise heads with support
- Ask patient to stay still, swallow, close eyes, place tongue on roof of mouth and keep it there, breathe through nose
What are some patient positioning problems that can occur when taking an OPG?
- Midsagittal plane not vertical (Head Tilted)
- Patient leaning forward (Neck not vertical)
- Head not centred (Rotated)
- Frankfurt Horizontal not horizontal (Chin Up/Down)
If interpretting an OPG via zones, what is the order to view the image?
Zone 1 - Nose and Sinus Mandibular Canal, Mental Foramen, Genial Tubercles Zone 2 - Mandibular Body Zone 3 - Upper Corners Condyles, Articular Eminence, Coronoid Notch, Mandibular Notch Zone 4 - Lower Corners Thyroid Cartilage Hyoid Bone Zone 5 - Mandibular Ramus and spine Zone 6 - Dentition
What terms would you describe an abnormality or pathology on an OPG?
Site Size Shape Border Centre Density - Radiolucent, Radiopaque, Mixed Impact on adjacent structure
What is a stafne bone defect?
Normal anatomical variant, the void in the mandible is created by ectopic salivary gland tissue associated with the submandibular gland
Not a pathologic lesion
