OPG Positioning Errors

Question 1

What is this positioning error?

Answer 1

Teeth in front of focal trough

• Artefact where anterior teeth or the hall arch is placed in front of the focal trough so you can see a lot of narrowing of teeth & a lot of spine is visible – should only be able to see anterior aspect of spine not entire spine
• When structures are in front of focal trough they look narrower

Question 2

What is this positioning error?

Answer 2

Teeth behind focal trough

• When teeth are behind focal trough they look more enlarged – magnified horizontally
• Cant see the spine at all because its out of the focal trough

Question 3

What is this positioning error?

Answer 3

Spine not straight

• no bite peg used (overlapping of teeth)
• Kyphosis of the spine or theyre not positioned correctly + neck is extended forwardly
• See a big white image right in the middle = ghost image of the spine
• Spine blocked the xray
• Teeth are also overlapped

Question 4

What is this positioning error (3 things)?

Answer 4

• Head tilting to the right
  
  • Incorrect midsagittal
  • Causes right side to be more inferiorly positioned compared to the left
• Chin down
  
  • Incorrect Frankfort plane
  • “Exaggerated smile” = Joker smile
  • Superiorly positioned hyoid bone
  • Condyles not visible (too high)
• Neck extension
  
  • Too much spine in the middle

Question 5

What is this positioning error (3 things)?

Answer 5

• Chin up
  
  • Incorrect Frankfort plane
  • “Reverse smile”
  • Condyles not visible – more posterior
• Neck extension
  
  • Too much spine in the middle – so get opacity
• Tongue not touching the palate
  
  • Palatoglossal airspace over the maxillary roots = lucency

Question 6

What is this positioning error?

Answer 6

Rotated to the right (incorrect midsagittal)

• Right-sided posterior teeth are behind the focal trough à horizontal magnification
• Asymmetry of the hemimandibles
• Opaque appearance of the left maxillary sinus
• Only right side structures are magnified
• Greater superimposition of turbinates over maxillary sinus
• When you see asymmetric maxillary sinuses, check if there was rotational error first
• If not then maybe pathology

Question 7

What is this positioning error?

Answer 7

Rotation to the right

RHS structures are more enlarged

Question 8

What is this positioning error?

Answer 8

Shoulder hit

Question 9

What is this positioning error?

Answer 9

Patient moved horizontally - deletion & doubling

• Deletion = When patient moves opposite direction to the x-ray beam
• Doubling = when patient moves towards the direction of the xray beam
• There is both deletion and doubling in this radiograph - 16 is doubled

Question 10

What is this positioning error?

Answer 10

Doubling of 74 & 34

due to movement towards the direction of x-ray beam

Question 11

Due to rotational nature of OPG, images can appear twice.

Depending on the locations, 3 different types of objects can appear, what are they?

Answer 11

Real, ghost & double

Question 12

What is a real image on an OPG?

Answer 12

• Object is between centre of rotation and receptor
• Sharper if closer to focal trough

Question 13

What is a ghost image on an OPG?

Answer 13

• Object between x-ray source and centre of rotation
• Usually outside of focal trough: appears blurred and magnified
• Appears on opposite side of image (L↔R) and higher on the image (due to upward beam) than their anatomical location
• Mandibular ramus, hyoid bone, cervical spine, earrings, etc.

Question 14

What is a double image on an OPG?

Answer 14

• Object is posterior to centre of rotation (the red diamond area) and intercepted by beam twice
• Structures in the centre eg. Hyoid bone, epiglottis, cervical spine, palate
• Double images are mirror images, appearing on the same location but opposite sides

Objects that lie posterior to the centre of the xray beam go through the centre of the beam twice and form a double image or mirror image appearing on the same location but on both right and left sides