Dear  FreeSurfers,<br><br>I am looking for a little help comparing longitudinal data. I have three timepoints on each patient and have been able to get individual spc-thickness maps using the long_mris_slopes command where my table included all three time points. I would however like to compare different timepoints with each other: tp3-tp2 and tp2-tp1. <br>
<br>I was hoping it would be as simple as specifying a new qdec table including (for example) only tp3 and tp2, and giving new output names using the following command <br><br>long_mris_slopes --qdec ./qdec/long.qdec.tableTP23.dat --meas thickness --hemi lh --do-avg --do-rate --do-pc1 --do-spc --do-stack --do-label --out-avg=long23.thickness-avg.mgh --out-rate=long23.thickness-rate.mgh --out-pc1=long23.thickness-pc1.mgh  --out-spc=long23.thickness-spc.mgh  --out-stack=long23.thickness-stack.mgh --out-label=long23.cortex  --time scan --qcache fsaverage<br>
<br>but I get the following error:<br><br>mris_calc:<br>    Sorry, but I seem to have encountered an error.<br>    While making backup of internal data arrays,<br>    it seems that some of the backups already exist.<br><br>
I&#39;m not really sure what the internal data arrays are, and would greatly appreciate any help.<br><br>Many thanks in advance and all the best,<br><br>Seán<br><br>