Hi Martin, Many thanks for your reply!
I did follow all the steps as described in the wiki. I'm not sure i understand your suggestion though.. Are you proposing that, instead of using the cross.qdec.table, i should use the longitudinal table to see the difference between two time points? My long.qdec.table looks like this: fsid fsid-base years M_b01_pre template_M_b01 0 M_b01_post template_M_b01 1.33 M_b02_pre template_M_b02 0 M_b02_post template_M_b02 1.33 M_b03_pre template_b03 0 M_b03_post template_b03 1.42 M_b04_pre template_b04 0 M_b04_post template_b04 1.58 M_b05_pre template_b05 0 M_b05_post template_b05 1.83 M_b07_pre template_b07 0 M_b07_post template_b07 1.33 M_b09_pre template_b09 0 M_b09_post template_b09 1.25 M_b10_pre template_b10 0 M_b10_post template_b10 1.25 M_b11_pre template_b11 0 M_b11_post template_b11 1.42 M_b13_pre template_b13 0 M_b13_post template_b13 2.08 M_b14_pre template_b14 0 M_b14_post template_b14 1.42 M_b15_pre template_b15 0 M_b15_post template_b15 1.33 M_b16_pre template_b16 0 M_b16_post template_b16 1.67 M_b17_pre template_b17 0 M_b17_post template_b17 1.33 M_b18_pre template_b18 0 M_b18_post template_b18 1.25 M_b19_pre template_M_b19 0 M_b19_post template_M_b19 1.42 M_b20_pre template_M_b20 0 M_b20_post template_M_b20 1.25 M_b21_pre template_b21 0 M_b21_post template_b21 1.42 M_b22_pre template_b22 0 M_b22_post template_b22 1.17 If i did that, qdec won't find long.thickness-rate...This measure as well as the other longitudinal measures (pc1, spc, etc) can only be found in the surf subfolders of the templates (fsid-base). What did i miss? Thanks for your patience, Joana 2011/9/23 Martin Reuter <mreu...@nmr.mgh.harvard.edu> > Hi Joana, > > actually it is possible, when using long_mris_slopes after running your > longitudinal data (I think that is what you did). > > I cannot judge if your table is correct. You did create that table from > the longitudinal qdec table as described on the wiki (longitudinal > tutorial) right? > So each line should be a template/base name and in the longitudinal > table there should be two entries for each of these templates. > > I notice that the years (here the average, so probably the distance in > time between your two time points) differs a lot (half a year to a year) > between subjects, that is of course not optimal. > > You can look at different things: > > difference per year (rate) > percent change per year with respect to baseline (pc1) > or percent change per year with respect to average thickness (spc, > called symmetrized percent change as it is symmetric). > > If you are interested in the change per year, long_thickness_rate is > correct. It accounts for the different time intervals. > You can then (in qdec) check if this is measure is different from zero. > > So everything you describe looks good. > > Best, Martin > > > On Fri, 2011-09-23 at 11:25 -0400, Douglas N Greve wrote: > > This is actually something that you cannot currently do in QDEC. Try > > doing a search for "paired" on our wiki for instructions on how to do > > this type of analysis. > > doug > > > > Joana Braga Pereira wrote: > > > Dear Freesurfers, > > > > > > I'm doing a longitudinal analysis of cortical thickness using the > > > newest version of Freesurfer and there is something i would like to > > > ask you all. > > > > > > I have two time points and only one group of patients. > > > > > > I've finished the pre-processing and am now searching for differences > > > between the two time points using Qdec. > > > > > > Since i only have one group my cross.qdec.table.dat file looks pretty > > > much like this: > > > > > > fsid years > > > template_M_b01 0.665 > > > template_M_b02 0.665 > > > template_b03 0.71 > > > template_b04 0.79 > > > template_b05 0.915 > > > template_b07 0.665 > > > template_b09 0.625 > > > template_b10 0.625 > > > template_b11 0.71 > > > template_b13 1.04 > > > template_b14 0.71 > > > template_b15 0.665 > > > template_b16 0.835 > > > template_b17 0.665 > > > template_b18 0.625 > > > template_M_b19 0.71 > > > template_M_b20 0.625 > > > template_b21 0.71 > > > template_b22 0.585 > > > > > > I selected the long.thickness.rate in Qdec interface and years as > > > continuous covariate since it is the only variable that i have in > > > my cross.qdec.table.dat (no groups or other covariates of interest). > > > > > > My question is: Is this the analysis i should be doing given that i > > > want to know the differences between time point 1 - time point 2? > > > > > > Many thanks, > > > > > > Joana > > > > ------------------------------------------------------------------------ > > > > > > _______________________________________________ > > > Freesurfer mailing list > > > Freesurfer@nmr.mgh.harvard.edu > > > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer > > > > > > The information in this e-mail is intended only for the person to whom it > is > addressed. If you believe this e-mail was sent to you in error and the > e-mail > contains patient information, please contact the Partners Compliance > HelpLine at > http://www.partners.org/complianceline . If the e-mail was sent to you in > error > but does not contain patient information, please contact the sender and > properly > dispose of the e-mail. > >
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