High Field and Spin Echo: the Minnesota story

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High Field and Spin Echo the Minnesota story

• Preview fMRI decision tree
• Why image at 7T?

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Cheng et al. (2001)
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Harrison, Harel et al., Cerebral Cortex 12225
(2002)
100?m
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Duvernoy et al., (1981) Brain Res. Bull. 7518
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BOLD fMRI is differentially sensitive to large
and small vessels
Spin echo sequences refocus dephasing caused by
susceptibility-induced gradients near large veins
Dynamic averaging regime diffusion of water
molecule is large compared to field gradient

• In both cases magnitude of field perturbation
  depends on
• field strength
• deoxyhemoglobin concentration

Static averaging regime diffusion of water
molecule is small compared to field gradient
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Spin Echo
180 deg.
90 deg.
M?
T2
T2
time (ms)
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Signal contributions gradient echo (T2)
Harrison, Harel et al., Cerebral Cortex 12225
(2002)
Extravascular protons near large vessels
Extravascular protons near small vessels
Relative contribution
100?m
Blood signal
Large venuole
Field strength
Small venuole/capillary
Intravascular
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Signal contributions spin echo (T2)
Extravascular protons near small vessels
Relative contribution
100?m
Blood signal
Large venuole
Field strength
Small venuole/capillary
Intravascular
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Other advantages of spin echo

• Refocusing of signal loss due to through-slice
  dephasing
• T2 instead of T2 contrast

SE
GE