Panoramic Radiology

Question 1

What type of radiograph is a panoramic radiograph (exta vs intra) and what is it designed to show?

Answer 1

Extraoral. Show the ENTIRE maxillomandibular region.

Question 2

What are other names for panoramic radiograph?

Answer 2

DPT, pantomogram,

orthopantomogram, panorex

Question 3

Do extra or intra oral radiographs have less of an issue with superimposition? Why

Answer 3

Intraoral because x-ray source and receptor can both be placed close to area of interest, hence less structures captured.

Question 4

What is the solution for superimposition?

Answer 4

Tomography which allows us to view “slices” of the subject separately.

Question 5

What are the two types of tomography? Which is used for panoramic radiographs?

Answer 5

There is conventional and computed. CONVENTIONAL used for panoramic radiographs.

Question 6

What are different types of tomography (other than panoramic radiographs) and what particle makes them?

Answer 6

• xrays: DPT, CT, CBCT
• radio waves: MRI
• gamma rays: SPECT (nuclear medicine)
• positrons: Pet (nuclear medicine)

Question 7

what is panoramic tomography

Answer 7

• form of CONVENTIONAL radiography developed to capture a curved slice aligned with the horse shoe shape of the jaws

Question 8

What is the shape of the x-ray beam of a DPT?

Answer 8

narrow, vertical, fan shaped.

Question 9

how does the receptor get exposed during a DPT

Answer 9

a different part of receptor is exposed at any one time.

Question 10

How is the area of interest exposed in a DPT vs intra-oral radiographs?

Answer 10

• DPT: area exposed SEQUENTIALLY from one side to the other over an extended time period (ex. 14 seconds).
• Intra-oral: area of interest exposed UNIFORMLY in a split second (ex. 0.2 seconds).

Question 11

What is a focal trough?

Answer 11

Structures in the focal trough will appear CLEARLY DISTINGUISHABLE/ in focus on image.

structures in focal slice remain projected onto the SAME point of receptor.

Structures outside this slice (more Ling or Bucc) will appear faint and spread out across the image.

Question 12

What is another name for “focal trough” in DPT?

Answer 12

tomographic slice of interest.

Question 13

What are the boundaries of the focal trough?

Answer 13

Focal trough a thin band where images appear adequately sharp.

NO DEFINED BOUNDARIES, sharpness progressively decreases as you move away (L or B).

Focal trough thinner in INCISOR region due to speed of rotation at this point, one of reasons whyINCISORS appear blurry.

Question 14

What is a limitation of using a focal trough to capture a slice?

Answer 14

ECTOPIC TEETH may be far enough out of the trough that they appear “missing”/ you wouldn’t know they are there unless other imaging is taken.

Question 15

What is the orthogonal program/ view? What examinations is it suitable for?

Answer 15

Aims to provide an optimal view of the dentition.

X-ray beam angulation changed to be more orthogonal/ 90 degrees to the teeth.

Only suitable for assessment of CARIES AND/OR PERIODONTAL BONE LEVELS.

Question 16

What are advantages of the orthogonal program?

Answer 16

• Less overlap between teeth (esp in PREMOLAR region) –> ASSESS APPROXIMAL CARIES.
• more accurately represents INTERDENTAL PERIODONTAL BONE LEVELS.

Question 17

What are disadvantages of the orthogonal program?

Answer 17

• distorts rest of skeleton
• typically narrower field of view so may miss condyles

Question 18

Why are panoramic radiographs magnified?

Answer 18

Because the x-ray beam is divergent.

Question 19

by how much are structures in the focal trough magnified? What about outwith?

Answer 19

In focal trough, structures magnified by 25%.

more BUCCALLY (to focal trough): magnified LESS
more LINGUALLY: magnified MORE

EFFECT IS EMPHASIZED AS DISTANCE FROM FOCAL TROUGH INCREASES.

Question 20

Which plane (horizontal vs vertical is more sensitive to DISTORTION)? What is the effect on the teeth?

Answer 20

Horizontal plane much more sensitive to changes in position due to continuous rotation of the machine.

more BUCCALY (to focal trough): teeth appear narrower
more LINGUALLY: teeth appear broader. (ex. when patient standing too far back in machine aka LINGUAL/BEHIND focal trough).

Question 21

Are teeth in the focal trough distorted? why/ why not?

Answer 21

No because the degree of horizontal magnification matches the vertical magnification.

Question 22

Which area is the MOST sensitive to distortion?

Answer 22

The anterior area as the focal trough is thinner.

Question 23

Why do teeth appear broader vs narrower?

Answer 23

Relates to how CLOSE they are to X-RAY SOURCE.

Appear broader when the tooth is LINGUAL/ CLOSER TO X-RAY SOURCE because x-ray source scans it for longer.

Narrower when the tooth is BUCCAL/ FARTHER FROM X-RAY SOURCE because x-ray source scans it for a shorter time.

Question 24

What is the position of the beam relative to the focal trough?

Answer 24

always LINGUAL to focal trough.

Question 25

What causes vertical projection? What is the effect of vertical projection?

Answer 25

Caused as the angulation of the beam is always angled slightly upwards, around 8 degrees above horizontal. Effect is that structures closer to the x-ray source. further from the receptor will be projected further UP ON THE IMAGE.

Question 26

3 benefits of DPT (compared to periapical)?

Answer 26

- Can capture entire dentition in one image - can image non dental areas (ex. rami, condyles, maxillary sinuses) - no need for intra-oral holders (gaggers, trauma cases, young children)

Question 27

3 disadvantages of DPT (compared to periapical)?

Answer 27

- worse quality (lower resolution, more superimposition, more artefacts) - longer exposure time (increased risk of patient movement) - higher radiation dose per image (approximately 5x more for a full panoramic radiograph compared to periapical).

Question 28

What criteria do you consider to decide between DPT vs periapical?

Answer 28

radiation dose, time taken, information obtained, technical difficulty. CHOICE DEPENDS ON WHICH GIVES BEST "CLINICAL BENEFIT TO RADIATION HARM" RATIO.

Question 29

what if field limitation?

Answer 29

Changing/ reducing the side of the area that is being irradiated.

Question 30

What must you do to position patient for DPT?

Answer 30

1. Remove metal foreign bodies from head and neck, ex. piercing, glasses, dentures, necklaces, hairclips 2. Position patient in machine - set machine at correct height - keep neck as upright as possible - position head using positioning apparatus - patient holds handles for stability. 3. Advise patient - do not swallow - stand still - keep tongue at roof of mouth

Question 31

What is the function of the bite peg?

Answer 31

Brings teeth into the same plane, aka into the focal trough.

Question 32

What are the 3 light beam markers used in DPT?

Answer 32

- Horizontal line must match FRANKFORT PLANE (infraorbital margin to upper margin of EAM). - Vertical mid-line must match MID-SAGGITAL-PLANE. - Canine lines must match MAXILLARY CANINES.