Basic principles MR
How does MRI works (physics):
1. Give energy to the system → excite proton spin
2. Turn off the source of energy
3. Observe the energy you get back thanks to entropy (rate of relaxtion)
Differences in relaxation = contrast
Rules:
Rule 1: Only magnetization in the transverse plane is measured
Rule 2: Rotation frequency scales linearly with local magnetic field strength
Rule 3: Relaxation processes determine contrast
Rule 4: Spatial localization based on spatial variation of magnetic field strength
, Rule 1: Only magnetization in the transverse plane is measured
The Z-axis is the direction of the magnetic field = Longitudinal magnetization
Magnetization will always return to Z-direction, when you wait a few second → equilibrium.
Magnetization in x-y plane = transverse magnetization (this is what will be measured)!
Water molecules will exhibit a net magnetization (M0) (= netto)
The main magnetic field direction:
Rule 2: Rotation frequency scales linearly with local magnetic field strength
Tesla (unit of magnetic field strength)
3 Tesla staat gelijk aan 128 Mhz (main field strength for clinical scanners)
7 Tesla staat gelijk aan 300 Mhz (very advanced research scanners)
Mhz staat voor het aantal rondjes dat de protonen maakt per seconde.
MR parameters of tissue determined by 3 parameters:
T = timing parameter
Proton density: number of protons that are present → more protons = brighter on image
(CSF)
How does MRI works (physics):
1. Give energy to the system → excite proton spin
2. Turn off the source of energy
3. Observe the energy you get back thanks to entropy (rate of relaxtion)
Differences in relaxation = contrast
Rules:
Rule 1: Only magnetization in the transverse plane is measured
Rule 2: Rotation frequency scales linearly with local magnetic field strength
Rule 3: Relaxation processes determine contrast
Rule 4: Spatial localization based on spatial variation of magnetic field strength
, Rule 1: Only magnetization in the transverse plane is measured
The Z-axis is the direction of the magnetic field = Longitudinal magnetization
Magnetization will always return to Z-direction, when you wait a few second → equilibrium.
Magnetization in x-y plane = transverse magnetization (this is what will be measured)!
Water molecules will exhibit a net magnetization (M0) (= netto)
The main magnetic field direction:
Rule 2: Rotation frequency scales linearly with local magnetic field strength
Tesla (unit of magnetic field strength)
3 Tesla staat gelijk aan 128 Mhz (main field strength for clinical scanners)
7 Tesla staat gelijk aan 300 Mhz (very advanced research scanners)
Mhz staat voor het aantal rondjes dat de protonen maakt per seconde.
MR parameters of tissue determined by 3 parameters:
T = timing parameter
Proton density: number of protons that are present → more protons = brighter on image
(CSF)
