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High Field and Spin Echo: the Minnesota story PowerPoint Presentation
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High Field and Spin Echo: the Minnesota story

High Field and Spin Echo: the Minnesota story

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High Field and Spin Echo: the Minnesota story

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  1. High Field and Spin Echo: the Minnesota story • Preview: fMRI decision tree • Why image at 7T? Spin Echo, high field

  2. Cheng et al. (2001) Spin Echo, high field

  3. Harrison, Harel et al., Cerebral Cortex 12:225 (2002) 100m Spin Echo, high field

  4. Duvernoy et al., (1981) Brain Res. Bull. 7:518 Spin Echo, high field

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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