Hi Freesurfer users,

For the longitudinal stream in FS5.1, there are only 4 options of measures (do-avg, do-rate, do-pc1 and do-spc). However, if I need other measures, such as the difference between two time points (thick2-thick1), how should I do to get the values and still be able to do the voxel-wise analysis for regional difference in cortical thickness (with glmfit)?

Many thanks

Keith
Postdoc research fellow
Toronto Western Hospital

  1. The temporal average is simply the average thickness: avg = 0.5 * (thick1 + thick2)

  2. The rate of change is the difference per time unit, so rate = ( thick2 - thick1 ) / (time2 - time1). 

  3. The percent change (pc1) is the rate with respect to the thickness at the first time point: pc1 = rate / thick1. 

  4. The symmetrized percent change (spc) is the rate with respect to the average thickness: spc = rate / avg.