> i have a question about atrophy correction of PET studies in a population
> affected by neurodegenerative disease.
>
> I get for each subjects a binary mask of segmented GM from MR scan. May I
> corrects by multiplying each PET images the binary mask of the same
> subjects ???
I'm afraid it isn't that simple. There are a number of approaches for making
such corrections, all with different model assumptions, advantages and
disadvantages:
1) Smooth the GM to same point-spread function as the PET, and divide the
PET image by this smoothed GM. The result is a measure of PET signal
per unit volume of GM. It is a very noisy measure, with problems
where the smoothed GM intensity is very low.
Assumptions: all PET signal is from GM
Labbé, M. Koepp, J. Ashburner, T.J. Spinks, M. Richardson, J. Duncan
and V.J. Cunningham , Absolute PET quantification with correction for
partial volume effects within cerebral structures. In: R.E. Carson,
M.E. Daube-Witherspoon and P. Herscovitch, Editors, Quantitative
Functional Brain Imaging with Positron Emission Tomography,
Academic Press, San Diego, CA (1998), pp. 59-66.
2) Trace out different regions of the MR image, creating binary images of
ones and zeros. Smooth each of these as above. Create a linear model,
of the form A*x = b, and solve for "x". Each column of "A" would
contain values from the smoothed regions. "b" would be corresponding
values from your PET data. "x" is the solution, which will be the
concentration of PET tracer in each region.
Assumptions: PET signal is constant in each region.
Positron emission tomography partial volume correction: estimation and algorithms.
Aston JA, Cunningham VJ, Asselin MC, Hammers A, Evans AC, Gunn RN
J Cereb Blood Flow Metab 2002 Aug 22:1019-34
3) Smooth the GM. Use the general linear model in SPM to look for PET differences
between groups, that can not be explained by GM differences.
Assumptions: Differences in PET/GM can be approximated by differences in PET-GM.
Richardson MP, Friston KJ, Sisodiya SM, Koepp MJ, Ashburner J, Free SL, Brooks DJ
& Duncan JS (1997): "Cortical grey matter and benzodiazepine receptors in
malformations of cortical development. A voxel-based comparison of structural
and functional imaging data." Brain. 120:1961-1973
There are other approaches out there. See also:
Meltzer, C. C., Kinahan, P. E., Greer, P. J., Nichols, T. E., Comtat, C.,
Cantwell, M. N., Lin, M. P., and Price, J. C. 1999. Comparative evaluation
of MR-based partial-volume correction schemes for PET. J. Nucl. Med. 40: 2053 2065.
http://www.arclab.org/medlineupdates/abstract_10616886.html
Best regards,
-John
--
Dr John Ashburner.
Functional Imaging Lab., 12 Queen Square, London WC1N 3BG, UK.
tel: +44 (0)20 78337491 or +44 (0)20 78373611 x4381
fax: +44 (0)20 78131420 http://www.fil.ion.ucl.ac.uk/~john
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