文档介绍：MRI - an introduction
Course: MR1 Biomedical Engineering (introduction)
Suggested reading: Haacke p. 1-15, hand-outs, J. Hornak’s
webpage: /htbooks/mri/
Author: Peter Vestergaard-Poulsen
Date: 2002
Version:
Sorry guys!!!
MRI = nonsense!
NMRI = nuclear ic resonance
imaging
..well, we’ll call it MR(I) anyway .........
An MR suite
RF-shielded
room
The - the ponent
Superconduc-
ting solenoide
in liquid helium
(ca. -269 ºC)
Strong static ic
field. 1-3 T (-
Gauss)
Radiofrequency coils (RF-coils)
RF-coils are used for
transmitting and
receiving signals to and
from the tissue.
Gradient system (ic field)
Linear ic
field gradients
are used retrieve
the signals from
their spatial
location.
Computer and control systems
Precessing of nuclear spins in a ic
field (Bloch & Purcell Nobel price, 1946)
Spinning nuclei acts like very small bar
s because they have a ic
momentum due the spinning charges (ic
dipole). When an external field is applied the
population of spins splits in two: parallel and
antiparallel to the applied field (the proton 1H
have spin ½ which gives two allowed energy
levels).
Net ic vector and phase coherence
The precessing
spins have no
phase coherence.
The sum of all
ic dipoles
gives
ization
vector M
The Larmor equation
The spins
Larmor frequency precess with the
Larmor
ù = ã B0 frequency.
ã is the gyro-
ic ratio
(isotope specific)
B0