Radiology 14 Flashcards
Names for panoramic radiographs
DPT, OPT/OPG
Tomography
Tomos “slice” + Graph “write”
Allows views of ‘slices’ of the subject to be viewed separately. Prevents issues of superimposing.
Conventional tomography
- “one slice”
- Not commonly used anymore except in panoramic radiographs
Computed tomography
- “multiple slices”
- Used in CTs etc.
- Mostly used
Basics of taking a DPT
- Patient stands still in the middle of the machine.
- X-ray source behind the head, and a receptor in front.
- Partially rotate round the head (roughly 180 degrees)
- Takes the image similar to a pano on iPhone (i.e over a few seconds) roughly 14 seconds.
Linear tomography: the principle of slice formation
Structures in “focal” slice remain projected onto same point of receptor.
Focal trough
The area most in focus, which is the teeth. The other structures like the tongue and lips are slightly stretched.
Focal trough in panoramic radiography
The point of rotation is moving during the acquisition to help create a curved focal trough.
What does this image represent?
The intensity of the colour reflects the sharpness of the image produced of that particular area. This is representative of the focal trough.
Anteriorly the focal trough narrows due to the speed of the machine spinning round the curvature - not uncommon for the incisors to end up rather blurry.
Limitations of focal trough in DPTs
Ectopic teeth man be far enough out of focal trough, so as to appear “missing”.
Example: the first and second images fails to pick up the tooth sitting in the palate seen in the third image.
Orthogonal view
X-ray beam angulation changed to be 90 degrees (orthogonal) to the teeth (horizontally and vertically.
Advantages: Orthogonal view
- Alleviates superimposition of the teeth which aids approximal caries assessment (particularly in the premolar regions which can often be more crowded)
- More accurate interpretation of periodontal bone levels because the x-ray beam is not passing obliquely through the alveolar crest.
Disadvantages: Orthogonal view
- Other anatomy can get distorted particularly the mid face region.
- Image is restricted to a smaller field of view which may crop out peripheral anatomy like the condyles (which may be of interest)
Advantages: can see less overlap in premolars especially.
Disadvantages: Maxillary sinus is superimposed with other structures, can’t see condyles.
DPTs: magnification
- Always inherently magnified due to the divergence of the x-ray beam.
- Within the focal trough the image is magnified by roughly 25%.
- Structures lingual to the focal trough are magnified more.
- Structures buccal to the focal trough are magnified less.
DPTs: Distortion
Teeth positioned buccally to the focal trough appear narrower.
Teeth positioned lingually to the focal trough appear broader.
*More sensitive anteriorly where focal trough is thinner.
*Structures within the focal trough are no distorted since the degree of horizontal magnification matches that vertically.
Why are teeth wider the more lingually they sit and narrower the more buccally they sit?
Advantages of DPTs
- Can capture entire dentition in one image
- Able to image non-dental areas (e.g. rami, condyles, maxillary sinuses).
- Lack of intra-oral holders benefits some patients (e.g. gaggers, trauma cases, young children)
Disadvantages of DPTs
- Worse clarity
- Longer exposure time (increased risk of patient movement).
- Higher radiation dose per image (approx 5x more)
panoramic vs full mouth periapicals
How can radiation dose be reduced when taking DPTs?
Field limitation (cropping down image)
Panoramic machine components
X-ray tubehead, receptor (usually digital), control panel, patient-positioning apparatus.
Panoramic machine: control panel options
- Field size
- Arch size/shape
- Position of machine (e.g. height)
- Position of patient-positioning apparatus
- X-ray tube exposure factors (voltage, amperage etc)
- Specialised use cases (bitewings, TMJ assessment etc)
DPT set up
- Remove metal foreign bodies from head and neck.
- Position patient in machine (set machine to correct height, hold handles etc).
- Advise patient (stand still, tongue to roof of mouth etc).
