Magnetic resonance imaging (MRI) is a medical imaging technique that uses magnetic fields and radio waves to produce detailed images of the internal structures of the body. MRI works by aligning the spin of hydrogen atoms in the body using strong magnetic fields and radio waves. When the radio waves are turned off, the hydrogen atoms send out signals as they relax and return to equilibrium, and these signals can be used to build up a detailed image of tissues and organs in the body. The basic steps of MRI involve applying a magnetic field to align spins, using a radiofrequency pulse to excite the spins and produce a signal, and detecting the signal as spins relax back to equilibrium.

1. BASICS OF MRI
Presented by:-
Pranali. N. Kulkarni
Ganesh M. Nair
Aaditee S. Kulkarni
Omkar Haldonkar

2. MAGNETIC RESONANCE IMAGING
 Magnetic resonance imaging
(MRI) is a medical imaging
technique used in radiology to
visualize internal structures of
the body in detail.

3. WHAT IS A SPIN????
 Atomic nuclei with an odd number of
protons behave like spinning particles
which in turn create a small nuclear
spin angular momentum.
 This angular momentum of an
µ : magnetic moment
Bo : magnetic flux density
electrically charged particle such as
the nucleus of a proton leads to a
magnetic dipole moment.
 These magnetic moments are
referred to as SPINS.

4. PRECESSION AND LARMOR FREQUENCY
 Acc. To electromagnetic theory
, nucleus of H2 proton posses
magnetic moments to align itself
with the magnetic field in which it
is field.
 This results in precession or
wobbling of magnetic moment
about the magnetic field with an
angular frequency called Larmor
frequency.

5. N N
Z Z
X,Y X,Y
S S

6.  MRI can be explained as interaction of spins with three magnetic
fields

7. BASIC STEPS OF MRI
1) 2)
3)

8. Z
STEP 1
Mz
STEP 2
M(t)
STEP 3
Y
Mxy
X
STEPS OF MRI

9. STEP 1
H
Z Mo
Mo= Equilibrium magnetization.
Mz = Magnetization along z. Anytime the
magnetization vector is displaced along z, it will be
called M.
Mxy= Component of M that is in XY plane

10. STEP 2
M can be displaced by applying a magnetic field H1
(rotating at Larmor freq of hydrogen nuclei)
 RF pulse causes:
At the end of 90 pulse, M=Mxy and Mz=0

11. STEP 3
RF pulse is turned off
Mxy diminishes towards zero
and Mz increases from zero.
After the 90 RF pulse,the
RF coil is switched to receiver
mode.

12. VOLTA FREE INDUCTION DECAY
GE
TIME

13. FREE INDUCTION DECAY
 At room temp. more protons are in a low
energy state.
 The excited proton tends to return to low
energy state with a spontaneous decay.
 This decay is exponential in nature