When to use MRI and CT Flashcards
Why do we need advanced images e.g., MRI or CT?
Use this case as an example
Allows for further and more detailed diagnosis
e.g.,
Radiograph - can identify vertebral bodies are not aligned (kyphosis) - distortion of ribs and dorsal spinal processes
CT - can see marked change in orientation of vertebral bodies has distorted vertebral canal
- can do curved reconstruction
what is curved reconstruction?
Using CT scans to obtain a dorsal slice of the spine to observe the relative shape of vertebral bodies
Identify the pathologies on this curved reconstruction CT scan
Gross malformation of vertebral bodies
Can see scoliosis of vertebral bodies
Compare CT vs MRI using this case as an example
Can see intervertebral disks and vertebral bodies in both
Can identify kyphosis on both
Can see spinal cord on MRI (outlined by white above and below = CSF + epidural fat)
Transverse MRIs used to see spinal cord (outlined in vertebral canal by CSF and epidural fat) - confirms no compression of the spinal cord.
CT much faster to obtain than MRI
Describe the difference between how a radiograph and CT image is taken
What are the disadvantages of radiography and CT scans?
Radiation dosing
Relatively poor soft tissue resolution
Describe the principles of how an MRI machine produces an image
What type of MRI is this?
T2
What type of MRI is this?
T1
What type of MRI is this?
T1 post contrast
What are the differences in contrast between T1 and T2 MRIs for these tissues?
High = white
Low = black
What are the disadvantages of MRIs?
Very susceptible to movement - not good for abdominal or thoracic cavities as they move
Relatively poor bone detail
Susceptible to metallic artefacts
Implanted medical devices
Much longer to get an image (takes 45 minutes)
What contrast media can be used in CT and radiography?
+ve contrast (Radiodense material) - Iodine/barium
-ve contrast (Radiolucent material) - air
What contrast media can be used in MRI?
+ve contrast (high signal material) - gadolinium (IV)
-ve contrast (low signal material) - air
When are CT scans used?
Need greater bone detail
Movement artefacts present
Patient incompatible with MRI
When are MRIs used?
For soft tissue detail
What is CT windowing?
The greyscale of CTs is changed to observe different tissues in greater detail
