Hi Chris,

Thank you for your response. Just to be clear that I'm interpreting your response correctly, would the following two conditions be true:

*A subject with axial acquisition and a "PhaseEncodingDirection: j" should have a sform_yorient="Poster-to-Anterior"

*A subject with axial acquisition and a "PhaseEncodingDirection: j-" should similarly have a sform_yorient "Posterior-to-Anterior".

If so, this indicates that sform_yorient provides information about the acquisition plane and will change based on polarity.

Thank you,

Jenna

Originally posted by Chris Rorden:

The sform_yorient informs you that the row order of the image data as stored on disk is Posterior-to-Anterior: it tells you how to map voxels to world space. In contrast, the polarity tells you the direction of the phase encoding. One expects the data to be stored with the same spatial frome of reference, regardless of the order rows are acquired.