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?. Cheng et al . (2001). Harrison, Harel et al., Cerebral Cortex 12:225 (2002). 100  m. Duvernoy et al., (1981) Brain Res. Bull. 7:518.

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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?

Spin Echo, high field


Cheng et al. (2001)

Spin Echo, high field


Harrison, Harel et al., Cerebral Cortex 12:225 (2002)

100m

Spin Echo, high field


Duvernoy et al., (1981) Brain Res. Bull. 7:518

Spin Echo, high field


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

Spin Echo, high field


Spin echo does not form – BOLD contrast is measured

Spin echo forms – BOLD

contrast is erased

Spin Echo

180 deg.

90 deg.

M

T2

T2*

time (ms)

Spin Echo, high field


Signal contributions: gradient echo (T2*)

Harrison, Harel et al., Cerebral Cortex 12:225 (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

Spin Echo, high field


Signal contributions: spin echo (T2)

Extravascular protons near small vessels

Relative contribution

100m

Blood signal

Large venuole

Field strength

Small venuole/capillary

Intravascular

Spin Echo, high field


Other advantages of spin echo

  • Refocusing of signal loss due to through-slice dephasing

  • T2 instead of T2* contrast

SE

GE

Spin Echo, high field


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