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Radiology > Radiology 12 - Extra-Oral Views > Flashcards

Radiology 12 - Extra-Oral Views Flashcards

1
Q

What are the most common extra-oral views?

A

Images relating to mandible: postero-anterior mandible, lateral oblique of mandible, DPT.

Images relating to maxilla and cranium: lateral cephalogram, occipito-mental views (0, 10, 30 degrees), sailography.

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2
Q

What do these acronyms stand for: AP, PA, OM?

A

Antero-posterior, postero-anterior (SPECIFY IT DOES NOT MEAN PERIAPICAL), occipito-mental.

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3
Q

What are the positioning landmarks used to help position a patient for extraoral radiography?

A

Radiographic base line: line from outer canthus of eye to EAM, represents base of skull.

Frankfort plane/ anthropological baseline: line from inferior orbital margin to upper border of EAM. USED FOR DPT.

Maxillary occlusal plane: line from ala of nose to tragus of ear. USED IN CONE BEAM CT.

(see slide 9)

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4
Q

What equipment do you need for extra-oral radiographs?

A

Skull unit (ex. satella) or cephalometric unit
High intensity/ highly penetrating beam
Image receptor (cassette with intensifying screens and film or digital system PSP cassette containing phosphor plate), anti-scatter grid.

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5
Q

What is Compton scattering?

A

When weaker x-ray photons are deviated off track as they do not possess enough radiation to pass all the way through to the receptor and make a useful interaction.

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6
Q

What can scattering cause?

A

Causes background fog (aka degrade the image), creating a greyer film which lacks contrast.

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7
Q

Why do we use an anti-scatter grid? What is it made of?

A

To stops photons scattered in the patient from reaching the film and hence prevent the degradation of the film. ONLY STRAIGHT HIGH E PHOTONS CAN PASS.

Made of alternating strips of lead and plastic. Can be fixed/ stationary (may be able to see it in final image) or moving/ oscillating (cant see on final image).

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8
Q

What do you need to consider when positioning a patient for EO radiography?

A
  1. Position of patient relative to film (facial views radiographic baseline 45 degrees, median sagittal line 90 degrees to film - skull radiography requires radiographic baseline to be 90 deg to film)
  2. Position of x-ray beam relative to patient (AP, PA, lateral).
  3. Position of x-ray beam relative to film (ex OM view at 10 deg to see orbits and at 30 deg to see zygomatic arches ad maxillae).
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9
Q

What are the indications/ why is a PA mandible useful?

A

Shows fracture of mandible (ex. mediolateral displacement at fracture site).

Also useful for cysts and malignancy causing expansion of bone destruction.

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10
Q

What structures can you see clearly in a PA mandible? Which ones not so much?

A

Can see posterior body of mandible and ramus clearly. Limited visualization of the condylar head and neck + midline obscured by spine.

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11
Q

What other view is a PA commonly requested with?

A

A DPT.

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12
Q

What are the benefits of taking a mandible film PA?

A
  1. reduces the magnification of the facial features on the receptor
  2. reduces dose to eyes (lens of eye is radiosensitive).
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13
Q

What is the correct patient positioning for a PA film?

A
  1. Patient faces film
  2. Nose and forehead touch film holder –> MAKES RADIOGRAPHIC BASE LINE HORIZONTAL/ 90 DEGREES TO THE FILM. (can tell this as mandible will appear long in radiograph - slide 31)
  3. Aim centre of beam to midline of patient at the height of mid ramus.

(see slide 29).

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14
Q

How do we find the midline of the patient?

A

Front: between the eyes (tip of nose unreliable as often deviates)

Back: external occipital protuberance.

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15
Q

Why do we need to have lateral OBLIQUE mandible?

A

(usually in radiography we do an AP or a PA and a lateral so that they are at 90 degrees)

Solely lateral image would superimpose the mandible. Must oblique mandible both in HORIZONTAL AND VERTICAL PLANES. Will only receive useful information from side closest to receptor.

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16
Q

What are the indications for a lateral oblique mandible?

A
  • Fractures of body, ramus, condyle.
  • Pathology (ex. cysts)
  • Assessment of wisdom teeth (although ideal is DPT)
  • dental assessment in special needs.
  • caries assessment in patients who cannot tolerate bitewing.
17
Q

What are the 2 methods for taking a lateral oblique mandible?

A
  1. Isocentric positioning using a skull unit or conventional x-ray unit (when investigating fracture in mandible)
  2. Dental tube with horizontal or vertical angulation (to visualize dental pathology).
18
Q

How do you take a lateral oblique radiograph in the isocentric position?

A
  1. position patient supine on the bed.
  2. rotate machine into the horizontal plane.
  3. angle x-ray tube 25 degrees towards the head.
  4. turn tip of patients head towards receptor/ the film.

CAN BE DIFFICULT FOR PATIENTS WITH BROAD SHOULDERS. VIEW NOT SUITABLE TO SEE TEETH. SEE SLIDE 58

19
Q

How do you take a lateral oblique radiograph in vertical angulation/ tube position?

A
  1. Patient holds cassette against and parallel to area of examination.
  2. Tube head is positioned beneath the lower border of the body of the mandible not under examination.
  3. Aim tube towards teeth to be examined. Angle tube slightly UPWARDS which will project the opposing body of mandible UP and away from the film.

(see slide 48)

20
Q

What are 2 disadvantages to vertical angulation lateral oblique radiograph?

A
  1. angulation can cause vertical distortion of teeth.
  2. maxillary teeth not always clearly shown.
21
Q

How do you take a lateral oblique radiograph in horizontal angulation/ tube position?

A
  1. patient holds cassette against and parallel to area of examination.
  2. tube is placed below the ear facing the RADIOGRAPHIC KEYHOLE (triangular space between the back of the ramus and the cervical spine - see slide 52) aiming along the occlusal plane towards the maxillary and mandibular teeth to be examined.
22
Q

What is the radiographic keyhole?

A

Triangular are between the back of the ramus and the cervical spine - see slide 52.

23
Q

What is the disadvantage of horizontal angulation lateral oblique radiograph?

A

X-ray beam may not directly pass between contact points, causing them to be overlapped on the image.

24
Q

What is cephalometric radiography?

A

Type of skull radiography in orthodontics to assess the relationship of the teeth to the jaws and the jaws to the rest of the facial skeleton.

25
Q

What are indications for cephalometric radiography?

A
  • Orthodontics assessment and pre-orthognathic surgery?
26
Q

What equipment is required to take a cephalometric radiograph?

A

can ONLY be taken using a CEPHALOSTAT UNIT.

ear rods are used to give standardized positioning and make the image reproducible.

27
Q

What are two must-haves for cephalometric radiographs?

A
  • must have means of calculating the amount of magnification of the image.
  • must be able to visualize soft and hard tissue.
28
Q

What are the 7 requirements for taking a lateral cephalogram?

A
  1. Mid sagittal plane parallel to receptor
  2. Frankfourt plane horizontal
  3. centre of beam aimed at the external acoustic meatus.
  4. teeth in occlusion.
  5. ear rods in situ
  6. ruler somewhere in the image (to help calculate magnification)
  7. Lead protection / Thyroid shield because the exposure factors/ dose required is high and hence thyroid gland should be protected.
29
Q

How can you reduce magnification? How can you calculate it on the final image?

A

Long source to patient distance/ focus to object distance (1.5 to 2m) and short patient to film distance.

To calculate magnification, you need a magnification rod or ruler in the image.

30
Q

Why can’t you normally see soft tissues in a lateral cephalogram?

A

Because the exposure required to penetrate lateral skull is so great than in normal circumstances it woudl not be attenuated at all by soft tissues and they would therefore not be visible on the image.

31
Q

What is done to ensure soft tissues are seen in a lateral cephalogram?

A

An aluminium filter is used

  • placed on anterior part of face, attenuates/ slightly absorbs the beam in the anterior facial region allowing for soft tissues and bone to be seen in one film.
  • in digital units this is done by software.
32
Q

How do you take a Postero-anterior cephalogram?

A

Same positioning as for a PA mandible (radiographic baseline parallel with floor) YET x-ray beam aimed at the middle at the level of the EAM.

Patient has rods in their ears.

33
Q

What are indications for occipito-mental views?

A
  • x-ray facial bones following trauma to rule out fracture.
  • most common fractures are of the zygoma, Le Fort fractures and orbital blowout.
  • can have a limited use in detecting pathology ex. sinus disease.
34
Q

How can you see all the bones in the face?

A

Different angulations are required. Standard is OM0, OM 10 and OM 30.

35
Q

How do you set up patient for occipito-mental views?

A
  • patient faces receptor
  • nose and chin touching receptor –> RADIOGRAPHIC BASELINE AT 45 DEGREES TO RECEPTOR
  • Aim centre of x-ray beam to midline of patient through base of nose.
  • Angle beam 10 or 30 degrees to feet (called CAUDAL ANGULATION - beam still exiting at the base of the nose in both views).

(see slide 77).

36
Q

What does increasing the angulation do?

A
  • Projects the dense bones of the skull base away from the facial structures.
  • improves the view of the zygomatic arches (PARTICULARLY IN OM 30).
  • Gives different perspective – may be useful for evaluation of bony displacement

OM10 AND OM30 ARE THE STANDARD FACIAL VIEWS.

37
Q

What does an OM 10 show clearly?

A

The orbits and the maxillary sinus walls. Can see body of zygoma. NOT useful for manidble.

38
Q

What does an OM 30 show clearly?

A

The zygomatic arches. Can also see the mandible but would not use this view to study the mandible.

39
Q

Can one view ever be considered in isolation?

A

No because a different view may show you a different injury as faces RARELY FRACTURE IN ONE PLACE!

Radiology (8 decks)

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