3dLocalBistat

AFNI Message Board
1

Hi,

I’m using 3dLocalBistat to generate a correlation (pearson) map between two 3D datasets. But I can’t find the corresponding t or p-value. Do you know where I can dig it up?

Thanks,
Phoebe.

2

Phoebe, could you show the output of the following command?

3dinfo -verb outputFrom3dLocalBistat

3

Hi Gang,

Thanks for your reply. There’s only one sub-brick with pearson coef (below ****).
Any suggestions?

Phoebe.

Identifier Code: XYZ_juIS0my9AELnTRN2fa1AeA Creation Date: Wed Jan 10 18:38:35 2018
Template Space: ORIG
Dataset Type: Anat Bucket (-abuc)
Byte Order: LSB_FIRST [this CPU native = LSB_FIRST]
Storage Mode: BRIK
Storage Space: 35,913,728 (36 million [mega]) bytes
Geometry String: “MATRIX(1,0,0,-129.6659,0,1,0,-162.3414,0,0,1,-54.31122):256,256,137”
Data Axes Tilt: Plumb
Data Axes Orientation:
first (x) = Right-to-Left
second (y) = Anterior-to-Posterior
third (z) = Inferior-to-Superior [-orient RAI]
R-to-L extent: -129.666 [R] -to- 125.334 [L] -step- 1.000 mm [256 voxels]
A-to-P extent: -162.341 [A] -to- 92.659 [P] -step- 1.000 mm [256 voxels]
I-to-S extent: -54.311 [I] -to- 81.689 [S] -step- 1.000 mm [137 voxels]
Number of values stored at each pixel = 1
– At sub-brick #0 ‘Pear cor’ datum type is float: -1 to 0.999583

----- HISTORY -----

4

Phoebe,

Try the following command:

3drefit -substatpar 0 fico X 1 0 YourFile

Replace X with the number of data points you used to compute the correlation at each voxel with 3dLocalBistat.

5

Hi Gang,

Thanks for your reply.

Unfortunately the '3drefit ’ command couldn’t append the fico parameters in the header of the dataset. But I have another question with this approach. I used the following 3dLocalBistat to output the dataset with Pearson correlation,

3dLocalBistat -nbhd ‘RHDD(6)’ -stat pearson -mask MASK+orig -prefix OUT A+orig B+orig

Since the volume of the rhombic dodecahedron with radius of 6mm is 432mm3 and the voxel size of A+orig and B+orig is 1x1x1mm3, the number of voxel pairs used in correlation analysis at the edge of the mask will be <432. Using a universal number of voxel pairs to derive the p-values may have a problem.

Any suggestions?

Phoebe.

6

Unfortunately the '3drefit ’ command couldn’t append the fico parameters in the header of the dataset.

What happened with the 3drefit command?

the number of voxel pairs used in correlation analysis at the edge of the mask will be <432

That’s true, but I would not worry it too much. When the number is large (e.g., greater than 100), the difference is negligible.