AFNI version info (`afni -ver`

): Version AFNI_23.1.07

Dear AFNI experts,

I tried to load a .nii file and convert to a physical size of array in python.

From what I checked, the size of the .nii file is (61,73,61) in (i,j,k) coordinate system, and the physical size of array should be (181, 217, 181).

1 <= i <= 61

1 <= j <= 73

1 <= k <= 61

-90 <= x <= 90

-90 <= y <= 126

-72 <= z <= 108

I thought there would be some matrix that maps the EPI data to a (i,j,k) coordinate system (.nii format), and if I multiply its inverse matrix to the .nii file, I could return the .nii file to the original size.

As Dr. Taylor mentioned in the post "ijk to xyz (voxel to mm) coordinate transformations", I ran the commands below and two 4*4 matrices were produced.

```
cat_matvec -4x4 pb08.s1.r01.scale+tlrc.::IJK_TO_DICOM_REAL (matrix A)
```

```
-3 0 0 90
0 -3 0 126
0 0 3 -72
0 0 0 1```
```

```
cat_matvec -4x4 pb08.s1.r01.scale+tlrc.::IJK_TO_DICOM_REAL -I (matrix B)
```

```
-0.333333 0 0 30
0 -0.333333 0 42
0 0 0.333333 24
0 0 0 1
```

So, I multiplied the matrix A to a vector (1, 1, 1, 1), but a vector (87, 123, -69, 1) was returned.

However, I am not sure about the result I got because I think that a vector (1,1,1) should be mapped to (-90, -90, -72).

I would appreciate it if you look into my question and answer it.

Jinsu Kim