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What are the angles reported from 3dvolreg?

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Q31. What are the angles reported from 3dvolreg?
The names are chosen from the angles used in describing the motions of aircraft or ships. (Imagine lying down with your arms out, pretending that you are an airplane. It is not necessary to make zooming noises during this mental exercise.)
  • Roll is the angle about the Inferior-to-Superior (I-S) axis. It corresponds to the motion one makes when shaking the head "NO".
  • Pitch is the angle about the Right-to-Left (R-L) axis. It corresponds to the motion one makes when nodding the head "YES".
    (This is the motion my Chairman is supposed to make when I ask for a large raise.)
  • Yaw is the angle about the Anterior-to-Posterior (A-P) axis. It involves rocking the ear towards the shoulder.
You could use the program 3drotate to move some dataset in each direction (one at a time) in order to see these effects.

The new [12 Feb 1999] program 1dplot makes it possible to graph the "-dfile" output from 3dvolreg to the display, and thence to a PostScript file. It can also be used to graph arbitrary *.1D format files, but for better control over such graphs, you should use program xmgr, available here, or use some other dedicated graphing program.

By the way, the displacement estimates output by 3dvolreg are in millimeters, and the angles are in degrees. This fact is mentioned in the output of 3dvolreg -help, but some people seem not to notice. One reason for these choices is that the typical FMRI experiment (at least with experienced normal volunteers) results in motions of about 1 mm and/or 1 degree, in my experience.

If you would like short description of how 3dvolreg works, see the end of file README.registration. For a longer description, you can download a PostScript preprint of a paper recently published in Magnetic Resonance in Medicine [Dec 1999].

[Answer last changed 10 Dec 1999]

This FAQ applies to: Any version.

Created by Robert Cox
Last modified 2005-07-31 23:13
 

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