[MURG] MRI resolution

[Eric Zilli]

A. with a 7T magnet you can get functional data at 1.2 x 1.2 x 3.0
mm^3 voxels.. with a 4T magnet you can get structural data at 0.9375 x
0.9375 x 4 mm^3 or functional data at 3.75 x 3.75 x 4 mm^3 (from 2
example studies I found)
the higher the magnet power, the higher the resolution you can get,
and structural (T1 weighted) is collected more slowly than functional
(T2*) so you get better resolution structurally (which is probably
what you're fater) at the same magnet strength

a 7T magnet like the one I mentioned above is very powerful and quite
rare.. most work is done with 1.5T or 3T magnets, but you asked for
the limit.. one problem may be that as magnets get more powerful, they
also get less safe.. I didn't even know humans could be used in a 7T
magnet until I found that study.. I thought it was considered too
unhealthy

B. someone else may have a better estimate, but I'd say if you can
image dendritic spines you're pretty close.. the smallest spine necks
can be as narrow as 40-50 nm, so we'd want a volume on that scale.. if
we use the 4T structural voxel size as standard, it'd mean we need an
improvement of about 18750 times to get to that scale (0.9375 mm / 50
nm)
remember that we can't use fmri at this scale: fmri is based on the
hemodynamic response, so it's really only meaningful on the scale of
blood vessels, much, much larger than this size
also keep in mind that mri improvements alone won't do.. to use this
route of noninvasive uploading probably also requires a high
resolution mr spectroscopy system because I think there's still a need
to extract information about receptor densities and such

C. this one I can't answer, I don't know enough to predict.. if
there's a moore's law sort of thing happening that cuts the volume of
a voxel down by 8 each year (i.e. each dimension halved), it'd take
about 15 years to get there.. but I very much doubt things are going
that quickly

keep in mind any of my answers could be wrong :)

On Sun, 28 Nov 2004 15:47:22 +0100, Giu1i0 Pri5c0 <pgptag at gmail.com> wrote:
> A) What is the current resolution limit that can be achieved by MRI on
> an object the size of a human brain (not on an extra-thin slice)?
> B) What is a realistic theoretical estimate of the MRI resolution
> required for mind backup applications?
> C) When do you guys think B) can be feasible?
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> MURG mailing list
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> http://minduploading.org/mailman/listinfo/murg
> 


-- 
Eric Zilli
Hasselmo Lab - Computational Neurophysiology
Center for Memory and Brain
Boston University
2 Cummington St.
Boston MA, 02215
digfarenough at gmail.com -- www.digfarenough.com