F mri

Functional Magnetic Resonance Imaging

Sources ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],[object Object]

fMRI technology is based on … ,[object Object],[object Object],[object Object]

The Physics of NMR Bloch (1946) and Hahn (1950) ,[object Object],[object Object],[object Object],= electron = neutron = proton

[object Object],[object Object],The Physics of NMR Bloch (1946) and Hahn (1950)

[object Object],[object Object],The Physics of NMR Bloch (1946) and Hahn (1950) proportionality constant for specific nuclear species (MHz/Tesla) strength of static magnetic field (typically about 1.5 Tesla) Nuclei Unpaired Protons Unpaired Neutrons Net Spin  MHz/T 1 H 1 0 1/2 42.58 2 H 1 1 1 6.54 31 P 0 1 1/2 17.25 23 Na 2 1 3/2 11.27 14 N 1 1 1 3.08 13 C 0 1 1/2 10.71 19 F 0 1 1/2 40.08

[object Object],The Physics of NMR Bloch (1946) and Hahn (1950) The precessing magnetization can be measured by a nearby coil.

[object Object],[object Object],[object Object],[object Object],[object Object],The Physics of NMR Bloch (1946) and Hahn (1950)

How does fMRI form an image of neural activity? How to form an image of neural activity using NMR? Need to measure: 1. Spatial Location 2. Neural Activity Magnitude

Spatial Location in 1-D ,[object Object],[object Object],[object Object],“ base” strength of the static magnetic field gradient strength of the static magnetic static field strength location in 1-D ,[object Object],[object Object]

[object Object],[object Object],Spatial Location in 1-D F [ s(t) ] measure s(t) frequency amplitude intensity

Spatial Location in 1-D Frequency Encoding in practice Phase Encoding

Spatial Location in 2-D Echo Planar Imaging (Mansfield 1977): use frequency encoding to determine the “ x” direction and echo encoding to determine the “ y ” direction. sampling windows

[object Object],Spatial Location in 3-D

How to measure neural activity? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Blood oxygen level dependent contrast (BOLD) (Ogawa et al. 1990) ,[object Object],[object Object],During periods of neuronal activity, local blood flow and volume increase with little or no change in oxygen consumption. As a consequence, the oxygen content of the venous blood is elevated, resulting in an increase in the MR signal.

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],so fMRI works like this …

Issues! There is not a one-to-one correspondence between T2 and the neural activity that we are trying to measure. There are pathways that might decrease the decay rate and hence results in a decreased MR signal!

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Issues!

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Dealing with the issues!

This figure relates the temporal and spatial resolution of methods for the study of brain function to the size scale of neuronal features and to the “invasiveness” of the methods. Comparison: temporal and spatial resolution; and invasiveness

How fMRI stacks up: ,[object Object],[object Object],[object Object],[object Object],[object Object]

F mri

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