| MAGNETIC FIELD 4: |
| Change in MR Signal over
time |
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| Local
signal change of a single voxel |
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| over
time is due to change in |
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| proportions
of |
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| oxyhemoglobin/deoxyhemoglobin |
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| PHYSIOLOGY |
| PHYSICS |
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| DEOXY HGB IS PARAMAGNETIC |
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| (Linus
Pauling, 1936) |
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| NEURAL
ACTIVATION |
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| IS
ASSOCIATED WITH AN INCREASE IN |
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| BLOOD
FLOW (Roy & Sherrington, 1890) |
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| AND DISTORTS THE LOCAL MAGNETIC |
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| FIELD
CAUSING SIGNAL LOSS |
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| RESULT: |
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| REDUCTION
IN THE |
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| PROPORTION
OF DEOXY HGB |
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| IN
THE LOCAL VASCULATURE |
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| RESULT: |
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| LESS DISTORTION OF THE MAGNETIC |
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| FIELD RESULTS IN LOCAL MR SIGNAL |
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| INCREASE |
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| Columbia fMRI |