[Mristudio-users] Quantify the head motion using the 4x4 transformation matrices from AIR results

[Yuan, Weihong]

Dear Susumu and all,

After registering the DWIs to b0 with AIR,  all the transformation matrices are saved in a text file (please see attached as an example) . Each DWI frame has a 4x4 transformation matrix, say it's called matrix A.  Here are my questions and I appreciate if you can help me with this:

- I assume the first three rows in the fourth column (element A(1,4), A(2,4) and A(3,4)) are for translation at x-, y-, and z- plane.  Can you confirm, please? Are they in the unit of mm or voxel? If I want to quantify the displacement, say for the 1st DWI frame relative to b0, can I just do: displacement = sqrt((x1-x0)^2+(y1-y0)^2+(z1-z0)^2)?

- The 9 elements in the first three rows and first three columns should be the rotation matrix.  Is there a way to get the quantification of rotation in the three plane (x-, y-, z-) for each DWI frame? I am wondering if you have a script that can read the text file generated from the AIR (see attached) and generate a text file with rotation (in three different plane) and translation for all the DWI frames?

Thanks

Weihong

Weihong Yuan, PhD
PNRC/IRC, Radiology
Cincinnati Children's Hospital
Cincinnati, OH 45040



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