Navigation in 3D slicer

Hello, I’m trying for weeks to do registration to a heart model… and its never seems to be accurate enough.
here is the process in which Im doing the registration:

  1. Im making a pivot and spin caliberation, usually Im not able to get a RMS smaller than 1, I apply the transformation to the needle
  2. I move the needle to a specific points on the model or making a route with the sensor on a specific vein then those point I collected is a point list called NP1
  3. then im making a new point list called LA(left artium) and put the point on the same locations that the needle was on the model
  4. Im using registration=> fiducial registration to make a transformation and choosing a linear transformation.
  5. I apply the linear transformation to the needle…

after this the needle is closed to where it suppost to be but there are some error- for instance - sometimes it goes out of the model when it is still suppost to be in the model
our model is elastic so we think this may be an issue - the model is moving sometimes - we are thinking of printing a harden model.
before we do that- is the process I describe seems ok? how can I improve it?

thank you for reading this and for all your help
Maya