Panoramic Radiography

Question 1

What is the panoramic radiograph designed to provide?

OPT, DPT

Answer 1

designed to provide a clear view of the entire maxillomandibular region

Question 2

What is superimposition?

Answer 2

Radiographs produced by passing X-ray beam through everything between X-ray source & receptor

All of these structures will be overlaid on the 2D image, potentially obscuring each other

Question 3

Why is superimposition less with intra-oral radiographs?

Answer 3

Less of an issue with intra-oral radiographs as X-ray source & receptor can both be placed close to area of interest (therefore fewer structures captured)

Question 4

What is tomography?

Answer 4

Tomography developed to allow “slices” of the subject to be viewed separately

solves superimposition

Question 5

What are the two types of tomography in medical imaging?

Answer 5

1. Conventional: one slice
   * Mostly obsolete in medicine except for panoramic radiographs
2. Computed: multiple slices

Question 6

What is panoramic radiography a type of?

Answer 6

Form of conventional tomography which was developed to capture a curved slice aligned with the “horseshoe” shape of the jaws

Question 7

Where does patient, x-ray and receptor stand?

Answer 7

Patient stands still in middle of machine
Controlled rotation of X-ray source & receptor around head during exposure
* Both remain opposite each other but point of rotation constantly shifts
* X-ray source remains primarily behind patient
* Receptor remains primarily in front of patient

Question 8

How is the area of interest exposed?

Answer 8

The area of interest is exposed sequentially from one side to the other over an extended time period (e.g. 14 seconds)
* This is in contrast to intra-oral radiographs for which the area of interest is exposed uniformly in a split second (e.g. 0.2 seconds)

Question 9

What type of tomography does panoramic use?

Answer 9

modified linear tomography

Question 10

What is linear tomography?

Answer 10

Linear tomography captures a single, flat slice by moving the X-ray source & receptor past the area of interest during the exposure

Question 11

How does slice formation occur?

Answer 11

X-ray source moves in one direction while receptor moves in opposite direction
Structures in a “focal” slice remain projected onto same point of receptor
Structures outside this slice are continually projected onto different points of receptor

Question 12

How will structures in the focal slice and structures outside the focal slice appear?

what is this called?

Answer 12

Structures in the “focal” slice will appear clearly distinguishable on image (focal trough)

Structures outside this slice will appear faint & spread out across image
* The further out, the worse the effect

Question 13

How does the focal trough appear?

Answer 13

Trough is essentially a thin band where images appear adequately sharp
No defined boundaries
* Sharpness continually decreases as you move further away (buccally or lingually) until objects eventually become imperceptible
Focal trough is thinner in the incisor region
* Related to the speed of rotation at this point
* One reason for why it’s not uncommon for incisors to appear blurry

Question 14

Which teeth may be far enough out of the focal trough so as to appear missing?

Answer 14

ectopic teeth

Question 15

What is the aim of a orthogonal program?

Answer 15

aims to provide an optimal view of the dentition

a clearer, full view of structures without distortion

Question 16

What is an orthogonal program?

Answer 16

X-ray beam angulation changed to be more orthogonal (i.e. closer to 90°) to the teeth

Question 17

What are the disadvantages and advantages of orthogonal program?

Answer 17

Advantages
* Reduces overlap of the teeth to aid assessment of approximal caries
* Particularly improves view of premolars (where dental arch curvature can be pronounced)
* Improves angulation to more accurately represent interdental periodontal bone levels

Disadvantage
* Distorts rest of skeleton to varying degrees (e.g. maxillary sinuses, mandibular rami)
* Typically a narrower field of view so may miss condyles at edge of image

Question 18

Where are orthogonal programs suitable?

Answer 18

Suitable for cases requiring only caries &/or periodontal bone loss assessment

Question 19

Within the focal trough, how much is the image magnified?

Answer 19

25%

Question 20

Magnification of structure lingual vs buccal to the focal trough?

Answer 20

• Structures lingual to the focal trough are magnified more
• Structures buccal to the focal trough are magnified less

Question 21

Due to distortion, what do teeth positioned buccal vs lingual to the focal trough appear?

Answer 21

Teeth positioned buccal to the focal trough appear narrower

Teeth positioned lingual to the focal trough appear broader

Question 22

Why are structures within the focal trough not distorted?

Answer 22

Structures within the focal trough are not distorted since the degree of horizontal magnification matches that vertically

Question 23

Why are teeth wider if lingual and narrower if buccal?

Answer 23

Relates to how close they are to the rotating X-ray source

Remember that the beam sweeps from one side of the jaws to the other but the X-ray source is always lingual to the focal trough

Question 24

What is vertical projection?

Answer 24

• The x-ray beam is not horizontal to the ground, it is tilted up slightly up, 8 degrees, as it passes from the back of the patient’s head to the front.
• This means structures positioned closer to the x-ray source will appear further up on the image.

Question 25

Why are panoramic better than periapicals?

Answer 25

• 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

Question 26

Why are panoramics worse than periapicals?

Answer 26

Worse clarity
* Lower spatial 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

Question 27

What are the main components of the panoramic machine?

Answer 27

• X-ray tubehead
• Receptor (usually digital)
• Control panel
• Patient-positioning apparatus

Question 28

What ar the common options on the control panel?

Answer 28

Field size
Arch size/shape
Position of machine (e.g. height) Position of patient-positioning apparatus
X-ray tube exposure factors
* Voltage (e.g. 60-90kV)
* Amperage (e.g. 4-12mA)
Specialised use cases
* “Bitewings”, TMJ assessment, etc.

Question 29

How to prepare before a OPT?

Answer 29

Remove metal foreign bodies from head & neck
* e.g. piercings, glasses, dentures, necklaces, hairclips

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

Advise patient
* Tongue to roof of mouth
* Stand still
* Do not talk or swallow

Question 30

What does the bite peg do?

Answer 30

• Forces patient into edge-to-edge occlusion
• Positions both arches in focal trough

Question 31

What do the light beam markers do?

Answer 31

• Horizontal line matches Frankfort plane (keeps chin level)
• Infraorbital margin→upper margin of EAM
• Vertical mid-line matches mid-sagittal plane
• Canine lines match maxillary canines

Question 32

What happens if the patient is slumped?

Answer 32

excessive cervical spine shadow

Question 33

What happens if the patient is too far forward?

into the machine

Answer 33

• Incisors now buccal to focal trough
• Incisors appear narrower

Question 34

What happens if the patient is too far backwards?

Answer 34

• Incisors now lingual to focal trough
• Incisors appear wider

Question 35

What happens during scan?

Answer 35

X-ray tube & receptor rotate part-way around head
“Full” panoramic radiograph typically takes 10-15s

Question 36

What must the patient do during the scan?

Answer 36

• Stay still
• Press tongue up against palate
• Not talk or swallow

Question 37

Is a lead apron necessary for patient?

Answer 37

There is no justification for the routine use of protective aprons for patients undergoing any form of dental radiography or dental CBCT imaging as the main X-ray beam should never be directed towards the abdomen. Doses to the patient or the foetus from scattered X-rays and leakage will then be negligible as will the associated risk.”
* Guidance Notes for Dental Practitioners on the Safe Use of Dental X-ray Equipment (2020