Raadiolo Flashcards
Def of MRI
Principle of MRI
- Works by magnetism (very high magnetic field).
what is Tesla?
Tesla (The unite of magnetic flux density)
- It represents the strength of a magnetic field.
1 Tesla = 20 thousand times earth’s magnetic field
Types of MRI machine
Magnetic field strength in MRI
CI of MRI
Contraindicated in patients with:
- Metallic prosthesis.
- Aneurysm clips.
- Cardiac pacemakers.
- Cochlear implants.
- Metallic foreign bodies in the orbits.
what are New implants (As pacemaker, Aneurysm clips, etc…) now made from?
- MRI compatible alloys possess no magnetic properties.
- So the patient can be safely introduced in the machine.
Advantages of MRI
Disadvantages of MRI
Clinical applications in MRI
Basic sequences in MRI
They are 3:
- T1 weighted (+Contrast).
- T2 weighted.
- Proton weighted.
what are other sequences in MRI?
Characters of basic sequences in MRI
- Very high resolution.
- Sometimes very slow (generally slower than CT), One sequence may take 2 minutes on the best machine.
- So not suitable for dynamic contrast exams because they take too long time.
To overcome this problem, we use gradient sequence
Acc to the mobility the amount of H+ in the tissue
(MRI)
How is fat Good & Bad in MRI? and How is thsi problem overcomed?
Def of Inversion Recovery Sequences
- Sequences used to null the signal from certain tissues.
what do Inversion Recovery Sequences include?
FLAIR: Used to null fluid (like T2 but with hypointense fluid).
STIR: Used to null Fat.
Characters of Gradient Echo
- Can be T1 or T2 weighted.
- Very fast
Uses of Gradient Echo
- Can be used in dynamic examinations.
- For example Dynamic liver exam → similar to Triphasic CT.
Importance of Heavy T2-Weighted Images
Examples of Heavy T2-Weighted Images
MRCP
What is Diffusion Weighted Imaging based on?
- based on: Measurement of the Random motion of water molecules in the inter cellular space “extracellular fluid” (Brownian movement).
Types of water motion
Directed motion
- Motion in certain direction as blood in blood vessel.
Random motion
- Motion in any direction as in extra & intra cellular fluid.
Findings in Diffusion Weighted Imaging
