T1:

1
Lecture 15 SUMMARY
Longitudinal magnetisation

• T1
• - Time constant for recovery of longitudinal
  magnetisation
• arises from random fluctuating B-fields in sample
  due to molecular motion of the molecules (and so
  spin with a magnetic moment).
• Measure using saturation or inversion recovery

M
M

M
(1-
exp
(-
t/T
))
z
Saturation recovery
z
o
1
M
o
Time after pulse
M
M

M
(1-
exp
(-
t/T
))
z
z
o
1
M
o
Time after pulse
Use 2nd 900 pulse to knock longitudinal
magnetisation into transverse plane to be
detected by receive coil along My.
2
Lecture 15 SUMMARY
Transverse magnetisation

• Dephasing arises due to three processes
• (i) T2 relaxation Arises from random fluctuating
  B-fields in sample. Described by T2 time
  constant.
• (ii) Chemical shift
• (iii) Inhomogeneities in static B-field
• Three processes lead to transverse time constant
  T2

- (ii) and (iii) refocussed by SPIN ECHO.
3
CPMG sequence
1800y
1800y
1800y
1800y
900x
t
t
t
t
t
t
t
Mxy
900x
Mxy Mxy0exp(-t/T2)
T2
T2
time
2t
6t
4t
4

• Magnetic Resonance
• Lecture 16
• 10) Nuclear Spin Relaxation
• B) MICROSCOPIC PROPERTIES
• 10.3 Mechanisms and Origin of Nuclear Spin
  Relaxation
• Theory and calculation of T1
• transition probablities