[Insight-users] deformation field interpretation, motion extraction

[c23562]

Dear All, 

I’m working on a project dealing with motion extraction from 4D- CT data of
human heart. 
After registration of two consecutive volumes I try to get the motion of
interesting points from deformation field. Therefore I fetch the deformation
vector out of the first field on the interesting position. With the result i
make a trilinear interpolation with the neigbouring deformation vectors of
the next field. And so on. The motion vector I write to a new field. But at
the end the optical flow doesn’t look like a possible motion of my
seedpoint.  What is going wrong? 
May I take the deformation vector [e.g. 0.3432 0.9387 0.6202] and interpret
it as a motion in x,y,z-direction? What is the right unit, pixel or
millimeters? At this time I assume that the unit is pixel and my seedpoint
moved 0.3432 to the next x-index, 0.9387 to the next y-index and 0.6202 to
the next 0.6202 z-index. Adding the the start position to the received
displacement I get the new position for the next deformation field pointing
to a non-grid position. Therefore I use trilinear interpolation between
displacement vectors of the neighbouring grid-notes to get the next motion
vector. 
Is it right to use the deformation field in this way or is there any
conversion of deformation field entries needed (negation, normalizing,
scaling, …) ? 
(For registration and creating the deformation field I used
DeformableRegistration5, DeformableRegistration15 and
DeformableRegistration16 .)

Best regards, 
Christian

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