Dear FreeSurfers,
I'm trying to replicate some functional analyses that were originally done in SPM2, and am using mri_volcluster. Here's my command: mri_volcluster --in Old8/bold/taumax30_2_21/tal-ffx/RSF_v_NIF/sig --in_type bfloat --reg Old8/bold/taumax30_2_21/tal-ffx/register.dat --thmin 3 --minsizevox 8.
I've noticed that the size (in voxels) and number of clusters changes if I play with the -sign flag. I am confused by this.
Here's the output not using the -sign flag:
Cluster Size(n) Size(mm^3) TalX TalY TalZ Max
1 28 1792.0 -19.80 -96.70 8.53 5.28907
2 8 512.0 39.60 26.79 -8.07 4.15380
3 9 576.0 99.00 16.69 -54.67 4.09661
4 10 640.0 87.12 63.11 18.95 -3.82155
5 13 832.0 67.32 -42.44 5.81 3.79067
6 11 704.0 -39.60 -16.43 59.78 -3.62503
7 11 704.0 -87.12 -75.98 -43.30 -3.59305
8 73 4672.0 43.56 -22.33 19.54 -3.43893
9 18 1152.0 43.56 -44.81 -41.49 -3.16065
10 8 512.0 -51.48 -32.30 53.20 -3.09981
11 15 960.0 -63.36 -20.49 56.30 -3.00613
12 48 3072.0 -71.28 -7.20 11.41 -3.00547
And here's the output with sign set to positive:
Cluster Size(n) Size(mm^3) TalX TalY TalZ Max
1 35 2240.0 -19.80 -96.70 8.53 5.28907
2 21 1344.0 39.60 26.79 -8.07 4.15380
3 13 832.0 99.00 16.69 -54.67 4.09661
4 10 640.0 -71.28 33.20 -35.31 3.91335
5 21 1344.0 67.32 -42.44 5.81 3.79067
6 9 576.0 35.64 -88.58 15.49 3.63267
Why does the size of the first cluster change? Also, where is cluster 4 from the second output in the first output? Is there some re-calculation going on here?
Dan Dillon, Ph.D.
Post-doctoral Fellow
Affective Neuroscience Lab
Dept. of Psychology, Harvard University
Phone: (617) 496-5222
E-mail: dillon@wjh.harvard.edu