Info requested on Neuroimaging

Harm-Jan Wieringa wieringa at compuserve.com
Tue Nov 3 10:38:00 EST 1998


Hello Luke,


> A neuroradiologist told me once that sometime in the next few years,
>fMRI is going to be done by imaging intracellular vs. extracellular
>sodium ions, which will remove this time lag.  It's a lot easier to get
>a strong signal from protons, and it is probably very difficult to
>distinguish intra- and extra-cellular from chemical shift (when it's
>chemical shift coming from atoms that aren't even in the same molecule),
>so my uninformed speculation is that the techniques they come up with
>might require high-budget specialized magnets, not the kind you find in
>most hospitals.  One thing of interest is that this technique would
>directly image neural activity, not blood oxygenation levels or
>something thought to correlate with neural activity...
>

If you can image those directly then, naturally, the hemodynamic time delay
is out of the picture. But you need high-resolution functional imaging, and
that takes time and probably a high-field. I know that in Japan they have 8T
scanners and will get a 14T one.
Normal ones can do anatomical scans up to about 1 mm. resolution (NOT
functional).

>> There are efforts on the way to combine both techniques. They may
supplement
>> each other. Some go even so far as to measure the EEG in the MRI scanner,
>> during an fMRI experiment.
>
> I've heard of that, but I didn't realize they did them both at the same
>time.  I wonder how they keep the two from interfering with each other?
>
See for instance http://www.neuro.com/neuroscan/prod06.htm

Duringt the RF pulse you do have distortion of the EEG, but that is usually
no problem. For instance for Epilepsy, you see the spike-wave in the EEG,
then start the fMRI scan and catch that brain activity in the fMRI (thanks
to the delay of the hemodynamic response).

Regards,
 Harm-Jan






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