MRI Foundation Flashcards
Why is MR so different from other imaging modalities?
MR uses no radiation and does not work based on absorption/reflection
Protons have a _____ charge and spins.
positive
The Principle Quantum number:
n
The Angular quantum number:
l
The Magnetic quantum number:
m
The Spin quantum number:
s
1 Tesla = _____ G (Gauss)
10,000 G
What is the magnetic field intensity of most clinical MR scanners?
10,000G (1T) - 30,000 G (3T)
What is resonance?
when two or more frequencies perfectly match
they amplify each other
What is the SPIN in MRI?
angular momentum and magnetic movement
True or false. Spins align with magnetic field.
True
The alignment of the magnets (“in the body”) can have two states:
Parallel to the magnetic field & opposite (anti-parallel) to the magnetic field
There are slightly more/less spins parallel to the magnetic field than anti-parallel.
There are slightly more spins parallel to the magnetic field than anti-parallel
The difference in the two spins give rise to the ___________.
net magnetization
Net magnetization depends on:
magnetic field, spin density (# of proton or water molecules), and temperature
Net magnetization increases/decreases with magnetic field.
increases
magnetic field & net magnetization are directly proportional
Net magnetization increases/decreases with spin density
increases
Net magnetization increases/decreases with temperature
decreases
What is relaxation?
The return to original status and the approach of and the approach of a total chaos
T1-Relaxation occurs on what magnetization?
longitudinal magnetization (up & down)
T2-Relaxation occurs on what magnetization?
transverse magnetization (side to side)
The rotation of a transverse magnetization will lead to an induction of a voltage in a ____.
receiver coil
T2- Spin-Spin Relaxation is also known as ___________.
Transverse relaxation
T1 Spin-Lattice Interaction is also known as _ .
Longitudinal relaxation
True or false. Every tissue has its own relaxation curve.
True
What is the Bloch Equation?
The equation for motion (for the magnetization)
What happens during T2 relaxation?
The “vanishing” of the transverse magnetization back to its original state.
What happens during T1-Relaxation?
“Recovery” of longitudinal magnetization back to its original state.
What happens during excitation?
An RF pulse is emitted from the scanner. The longitudinal magnetization decreases and transverse magnetization appears. This makes the protons go to a higher energy state (parallel to anti-parallel)
True or false. Normally, protons in the body are oriented randomly. But, when in a MR scanner, they are aligned.
True
What occurs during recovery?
Protons return back to low energy state, restoring longitudinal magnetization
What happens during De-phasing?
The signal is sent back. T2-relaxation occurs.
What is precession?
The rotation of a spinning particle upon its axis in the presence of a magnetic field. The speed at which the proton is rotating.
Precession can be expressed by what equation?
Larmor frequency equation
What is Larmor Frequency?
The frequency at which a spin precesses about an external magnetic field (Larmor frequency = Precession frequency)
Larmor Frequency is dependent on type of ___ and ___.
nucleus; strength of magnetic field
What is the Larmor Equation?
v = y * Bo
Precession Frequency = gyromagnetic ratio * magnetic field
they are directly proportional
Why Hydrogen?
- Hydrogen has the highest gyro-magnetic (y) ratio among the nuclei (strong signal)
- it’s 99.9% abundant
- Our body constitutes of 60% water
- Present in nearly all other organic molecules in our body
