Principles of MRI Flashcards
What is MRI good for visualising?
Soft tissue detail
When is MRI inappropriate?
When an animal has a metal implant
Why do we used advanced imaging?
Allows us to view ‘slices’
How does MRI work?
- Magnets produce strong magnetic field
- Protons in the body align with the field
- RF pulses stimulate protons and they spin out of equilibrium
- When pulse is turned off, protons realign with magnetic field
- Energy is released when the protons return to equilibrium
What is a T1 Scan
Short repetition time
What is repetition time?
The gap between RF pulses
What is a T2 scan?
Longer repetition time
How does the type of scan affect the image?
T1 scan - shorter repetition time, hasn’t spun back before next RF pulse
* Therefore fluid appears dark on T1
How does fat appear?
Always bright
Quick to relax
How does bone appear?
Always dark (doesn’t have high water content)
How does fluid appear?
T1 - dark
T2 - bright (has time to relax before next pulse)
How does pathology appear?
T1 - dark
T2 - bright
Problems with MRI
- Very susceptible to movement
- Relatively poor bone detail
- Metallic artefacts
- Implanted medical devices (Metal)
+ve MRI contrast media
High signal material
* Gadolinium given IV
-ve MRI contrast media
Low signal material
* Air
