Lecture 6 - Extraoral Imaging Flashcards
When should a CBCT or a Pano be taken?
To evaluate the teeth when there is no need for high resolution and/or sharp detail
- Trauma
- Third molars
- Disease
- Anomalies
- TMJ
- Pt can’t tolerate intramural radiographs
- Sinuses
Advantages of panos vs FMX?
Broad coverage of facial bones and teeth
Low radiation dose - ~16 microSV vs 35-170 microSV
Quick and convenient
Disadvantages of panos.
Lower resolution
Magnification is unequal
Some image superimposition
What is the focal trough?
A zone of sharpness
- The nearer a structure is to the middle of the focal trough, the clearer the resulting image
- Structures outside the focal trough are blurred, magnified, reduced in size, or distorted
T/F - Pano images are inherently distorted in both size and shape, making measurements highly unreliable.
TRUE
- Influenced by
- Beam angulation
- X-ray source to object distance
- Path of rotational center
- Poistion of object w/in the focal trough
What are ghost images?
Objects that are located b/t X-ray source and center of rotation
*Typically blurred, magnified, located opposite the anatomic structure on the film
Tell me about pano positioning for a patient.
Incisal edges into notched positioning block
Center mid-sagittal plane
Upright, centered head
Infraorbital foramen line parallel to floor
Spine erect
Tongue to roof
Why take intraoral bitewings over extraoral bitewings?
The fine details are still hard to make out/resolution isn’t as good still
What is a cephalometric?
Lateral skull film
T/F - MRI has NO radiation.
TRUE
MRI?
PET?
CT?
MRI - Magnets - NO RADIATION
PET - Nuclear - Gamma rays emitted by a tracer
CT - A lot of radiation - X-ray moving on a fixed axis
CBCT. What is it?
Cone beam CT - X-ray beam shaped like a cone rather than a fan
What’s a voxel?
3D pixels
.4 voxel needs 1 photon to turn it to a latent image.
.2 voxel needs 8 photons to turn it to a latent image (resolution is better though)
.1 voxel needs _____ photons to turn it to a latent image.
64
T/F - You can change the size of the X-ray you are taking with CBCT
TRUE
T/F - Larger the volume, the higher the dose to the pt.
TRUE
T/F - The smaller the voxel size, the higher the dose t often pt.
TRUE
T/F - You should use the smallest volume and largest voxel size that will generate the diagnostic image you need in order to keep the radiation dose to the pt as low as possible.
TRUE
When do we use a cone beam?
Assessment of the jaws
Facial structures for ortho
TMJ
3rd molars
What is the effective dose from CBCT?
6 - 477 microSV
*On average ~200 microSV
