Magnetic Resonance Imaging

Spin Packets

A group of spins experiencing the same magnetic field strength.

---

The magnetization vector for a spin packet is proportional to (N⁺ - N^-)

---

Net Magnetization

Sum of the magnetization from all the spin packets.

---

Conventional NMR Coordinate System

---

Let's stop drawing the pole pieces.

B_o = applied magnetic field
M_o = Equilibrium magnetization
M_z = Longitudinal magnetization
M_xy = Transverse magnetization

---

T₁ Processes

If M_Z is set to 0.

---

M_Z wants to return to equilibrium.

---

M_z = M_o ( 1 - e^-t/T1 )

---

Spin-lattice relaxation time (T₁)

Time constant which describes how M_Z returns to its equilibrium value.

The time to reduce the difference between the longitudinal magnetization (M_Z) and its equilibrium value by a factor of e.

---

When magnetization starts at -Z axis...

M_z = M_o ( 1 - 2e^-t/T1 )

---

Copyright © 2000 J.P. Hornak.
All Rights Reserved.