Download data acquisition in 2D-3D: MRI

data acquisition in 2D-3D:
MRI
MRI: Magnetic Resonance Imaging
CT and MRI
Visible Human
MRI: magnetic resonance imaging
(NMR: nuclear magnetic resonance)
Kernspintomographie
strong magnet
RF pulse generator
receiver coil
• 
change in direction of magnetization induces electric current in external coil
Spin
•  spin: fundamental phyiscal property of elementary
particles (electrons, protons, neutrons) with states
-1/2 or +1/2
•  electron spin:
–  orbital model
–  Pauli principle
–  ions
•  nuclear spin: nuclear orbital models
–  e.g. H-atom:
•  net spin = 1/2
•  abundant in biological tissues --> MRI signal generation
Spin and magnetic field
N
N
S
-
S
+
+
-
+
-
-
state transition and energy
energy
N
S
N
N
S
ΔE=hν
resonance
frequency
(Larmor frequ.)
S
RF: radio frequency
spins at the macroscopic level
•  without external magnetic field: total spin=0
•  with external magnetic field: nr. of antiparallel
spins > nr. of parallel spins
–  → net magnetization of the system
•  energy injection with radio frequency (RF)
pulse
–  → facilitates state transition
–  → results in deflection of magnetization direction
changing the magnetization
+
+
RF pulse
-
-
MRI signal
RF pulse
external magnetic field
inductive
coil
+
+
-
-
current
excitation - relaxation
T1 and T2 signals
•  T1: longitudinal magnetization time constant
•  T2: transversal magnetization time constant
MRI
T1
T2
recovering spatial information
•  application of magnetic field gradients in x,y,z
MRI signal
•  change in direction of magnetization induces
electric current in external coil
image reconstruction
•  via back-projection (in Fourier space)
CT
MRI