MRI basics Flashcards
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In what is MRI based?
In nuclear magentic resonance phenomenon.
What is the advantage of MRI respect CT?
It achieves great contrast between tissues
CT is based in density and can’t distiguish similar tissues.
Does the magnet stops functioning during vacations?
It NEVER TURNS OFF
In waht type of atoms is MRI based?
In hydrogen atoms.
By which process do atoms return to the stable state?
Precession
Spiral/Helicoidal transition
What is the Larmor frequency?
It is a constant angular velocity by which atoms return to its stable state.
Specific for each atom.
After the emission of the RF wave the magnetization is purelly…
How is the magnetic moment vector orientes?
Transverse
T1 is the time needed for the Z component to reach —% of it’s maximum value.
Transversal
63%
T2 is the time need for transverse magnetization to fall to —% of its initial value.
37% (1/e)
What do gradients produce in MRI?
Sightly alterations of the B intensity at each point, which produces waves slightly different at each point.
Allows to make an image
Is the signal intensity measured in MRI allways the same?
No, it’s variable
Depends on the tissue, the equipment and the sequece used.
How long does it take in a MRI to acquire the different sequences?
Half an hour
What is the main risk in an MRI?
The presence of ferromagnetic materials (transplants..)
What does SAR measure?
The amount of energy absorved per mass unit
(W/kg)
