Other Imaging

Question 1

how does a medical CT work?

Answer 1

X-ray source and detectors continually rotate around patient.. As this rotation occurs, the patient is moved as shown below…the combination of these movements produces what is called “helical” or “spiral” image.

Question 2

compared to CBCT, “medical” CT:…?

Answer 2

1. Uses more expensive equipment
2. Produces higher dose for the same “volume” imaged.
3. Provides better soft tissue resolution.
4. Does not have “isotropic” voxels.

Question 3

how is the image interpreted for CT?

Answer 3

Software interprets the degree of x ray absorption and sets up three-dimensional “volumetric” data that can be viewed as a 3D image, or in any anatomic plane that is desired.
2D elements are called “pixels”.
The 3D elements are called “voxels”

Question 4

What does the software do for each tissue?

Answer 4

Each tissue is assigned a
“number” by the software that indicates its x ray absorption characteristics..
Air -1000
Water (soft tissues) 0 Cortical bone +1000

By adjusting the range of densities that can be visualized, we can see image in “bone window” (left) to see bony structures better, or in “soft tissue window” (right) to see soft tissue structures better.

Question 5

how does CBCT (cone beam CT) work?

Answer 5

CBCT – Cone (or pyradmidal) -shaped x ray beam and flat sensor (detector).
300 + individual exposures are made around the anatomical area. Information reconstructed into “volumetric” data that can be viewed as a three-dimensional image, or in any anatomical plane.
Both medical and cone-beam CT data can be used to provide three- dimensional reconstructions, or reformatted images in any anatomical plane.
Bone windows look similar with both types of CT. However, soft tissue contrast is not as good with CBCT as with medical CT, so soft tissue windowed images are usually not produced with CBCT.

Question 6

MRI machines look like CT units, but the technique is quite different, how is it different?

Answer 6

• NO ionizing radiation used
• Imaging done by subjecting body to strong magnetic field, applying a radiofrequency pulse to the tissues, then reading the “signal” or energy emitted from the body

Question 7

how are CT, CBCT, and MRI at different things?

Answer 7

• CT good for bone imaging
• Medical CT can provide some soft tissue resolution
• CBCT images have poor soft tissue resolution
• MRI better for soft tissue imaging
• As with CT, MRI data can be reformatted into various anatomical planes