How was that missed? (Mandibular Fracture)

This how was that missed post is showing a case of a mandibular fracture missed on a 2D image but easily seen on a CT scan.

Initial interpretation: Obvious radiolucent line extending from mandibular left premolar region to the inferior border of the mandible.  There is a discontinuity of the inferior border at this spot. The radiograph shows a single mandibular fracture of the left body.

Scout view for CT

Axial view showing two fractures of the mandible (white dotted and orange arrows)

Final Interpretation: (after reviewing CT scan) There is not just one but two fractures of the mandible creating a segmental fracture of the mandible.  While the left fracture (orange arrow above) was easily seen on the pantomograph, the right fracture (white dotted arrow) was not as obvious.

Lesson learned: The second fracture (right) shows the least common way fractures present on radiographs – increased radiopacity due to overlapping of the two segments.  This case was good in reminding me of that specific radiographic finding of fractures.  After seeing the CT scan and going back to look at the pantomograph, you will note there is a radiopaque U shaped entity near the right antegonial notch region.  This is where the two segments of the mandible overlapped.  Go here for a reminder of the 4 radiographic findings of fractures.

If you have any questions about this case or radiographic findings of fractures, please let me know. Thanks and enjoy!


SLOB rule (Same-Lingual, Opposite-Buccal) using vertical angle changes

This post was in request to an example of how to use the SLOB rule with vertical angle changes.  So here we go.

SLOB rule with vertical angle changes

When referring to vertical angle changes, the images are described as inferior (shows more inferior objects) or superior (shows more superior objects).  For example, using two radiographs, a mandibular molar periapical radiograph and a molar bitewing radiograph, the mandibular molar periapical radiograph would be to the inferior and the molar bitewing radiograph would be to the superior.  Below is an example with a metallic restoration (marked with a blue star) on the mandibular first molar and the steps used for this rule.

1) Using the two images above identify one as image 1 (mandibular molar periapical radiograph) and one as image 2 (molar bitewing radiograph).

2) Select two things that are visible on both images – 1) a fixed or known object (occlusal metallic restoration on mandibular first molar) and 2) the unknown object (metallic restoration with blue star).

3) Determine which direction the images appear to move from image 1 to image 2 (superior).

4) Next determine where the image of the unknown object (blue star) moves in relation to the fixed object (occlusal metallic restoration) from image 1 to image 2 – the metallic restoration moves inferior (image 1 to image 2) compared to the occlusal metallic restoration.

5) Using the SLOB rule (same-lingual, opposite-buccal) this shows that the unknown object image moves in the OPPOSITE direction as the images (1 to 2) and therefore it is to the buccal of the occlusal metallic restoration.

Using vertical angle changes with the SLOB rule takes practice (as does any image shift exercise).  Keep an eye out for each Monday in November as I will be posting practice examples for you to try out and test yourself.

Should you have any questions or thoughts on this topic, please let me know.

Thanks and enjoy!

Attenuation: Photoelectric Effect

This is the last post on attenuation methods.

Photoelectric effect

There are three main steps in photoelectric effect.

1. A high energy incoming x ray photon knocks out an orbital electron (diagrams show K shell electron being knocked out). The energy of the x ray photon must be equal to or greater than the binding energy of the orbital electron.

2. The electron knocked out of it’s orbit is called a photoelectron.  The photoelectron loses its energy as heat in the object being imaged.

3. The atom now has an empty orbital electron.  The electrons from other orbitals will jump the shells (i.e. L shell to K shell or M shell to K shell, etc.).  This produces characteristic radiation within the object being imaged.  This cascade of electrons continues until the atom has filled all it’s empty shells.

Incoming x ray photon knocks out K shell orbital electron.

K shell orbital electron is now a photoelectron.

L shell orbital electron ‘jumping orbitals’ and filling in K shell.  Produces characteristic radiation when ‘jumping orbitals’.

M shell orbital electron ‘jumping orbitals’ and filling in L shell.  Produces characteristic radiation when ‘jumping orbitals’.

The quantity of photoelectric effect occurring within an object is determined by the third power of the atomic number of the absorber. This method of attenuation accounts for approximately 30% of all attenuation.

Should you have any questions about this, please let me know.  Thanks and enjoy!

Next week: How was that missed – TRAUMA!