Alignment of tilt series

Alignment of images tilt series used in 3D tomographic reconstruction
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Alignment of images tilt series used in 3D tomographic reconstruction


Tomography is a method in which a 3-D structure is reconstructed from a series of 2-D projections (images) acquired at successive tilts (Radon 1917).
Involves similar principles to those used in light microscopy, electrons are used for illumination instead of photons.
Electron microscopy (EM) reveals basic specimen structures in details, reaching a better resolution than light microscopy, however Electron Microscopy provides only 2D projection views of the specimen.
Electron microscopes record projection images, a single image is information from all heights of the specimen collapsed onto a single plane, then a series of images is acquired, by varying the orientation of the specimen relative to the incident beam, such series contain all the information required to describe the 3D structure of the imaged object. For each angle, the projection images are saved, the 3D reconstruction is done by backprojecting the projection views.
The rotation of specimen is not ideal, because of mechanical inaccuracies of the specimen holder, this causes a misaligned set of images.
It's necessary to have a set well aligned in order to obtaind a good result in the reconstruction phase.
To align the tilt series, first maximize a “similarity” function(i.e. cross correlation, mutual information), then shift the images according to the position of the peak value of the similarity function.