BASICS OF MRI Presented by:- Pranali. N. Kulkarni Ganesh M. Nair Aaditee S. Kulkarni Omkar Haldonkar
MAGNETIC RESONANCE IMAGING Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to visualize internal structures of the body in detail.
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 anµ : magnetic momentBo : 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.
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.
N N Z Z X,Y X,YS S
MRI can be explained as interaction of spins with three magnetic fields
BASIC STEPS OF MRI1) 2) 3)
Z STEP 1 Mz STEP 2 M(t) STEP 3 Y MxyX STEPS OF MRI
STEP 1 H Z MoMo= Equilibrium magnetization.Mz = Magnetization along z. Anytime themagnetization vector is displaced along z, it will becalled M.Mxy= Component of M that is in XY plane
STEP 2M 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
STEP 3RF pulse is turned offMxy diminishes towards zeroand Mz increases from zero.After the 90 RF pulse,theRF coil is switched to receivermode.
VOLTA FREE INDUCTION DECAY GE TIME
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