Problem with vtkImageSlice and vtkPicker.js

Hi guys,
I am trying to add a mouse to world coordinates detection with vtkPicker, to get the pixel on reslice that the mouse is passing, to example:

but it detect the intersection around a margin outside of the slice, I think is that the camera generate is in perspective but I cannot force to parallel even using obj.renderer.getActiveCamera().setParallelProjection(true);

Any solution about this?

Thanks in advance for any suggestion.