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

High Field and Spin Echo: the Minnesota story

  • Preview: fMRI decision tree

  • Why image at 7T?

Spin Echo, high field


Cheng et al 2001

Cheng et al. (2001)

Spin Echo, high field


High field and spin echo the minnesota story

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

100m

Spin Echo, high field


High field and spin echo the minnesota story

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

Spin Echo, high field


Bold fmri is differentially sensitive to large and small vessels

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

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 t 2

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 t 2

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

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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