·
Also called spin lattice
relaxation
·
Release of energy by the
excited spin/proton to the local tissue
·
Basically the longitudinal
re-growth of MZ (longitudinal magnetization – the component of the
proton’s magnetic moment parallel to the applied external magnetic field – at
maximum equilibrium = M0, with amplitude determined by excess number
of protons in the lower energy state)
·
The T1 constant of a
tissue is the time needed for protons/spins of a specific tissue to return to
63% of the M0 following a 90O RF pulse
·
After a time of 5x T1
the sample is considered to be back to full M0 (back to equilibrium)
·
Because only MXY (transverse
magnetization) can be measured, repeated 90O pulses with different
delay times data points that lie only the T1 recovery curve can be determined
·
T1 Depends on the
characteristics of the spin/proton interaction with the lattice (molecular
arrangement or structure) and the number of protons available for the
transition
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T1
|
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General time
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Long
|
|
Large; slowly vibrating;
bound molecules
|
Long
|
|
Intermediatly sized,
vibrating and bound molecules (Viscous materials – lipids/proteins/fats)
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Short
|
|
Small; fast vibrating;
free molecules
|
Long
|
|
Influence of magnetic
field strength (increase)
|
Increase
(Related
to dependence of Larmor frequency on mag. Field strength and degree of
overlap with molecular vibration spectrum (decreases with increased mag.
field)
|
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Paramagnetic blood
degredation products; gadolinium; ferromagnetic materials
|
In
situations when macromolecule binds free water in a hydration layer –
++ Shorter
|
