Discrete tomography of demanding samples based on a modified SIRT algorithm.

The 3D structure of three particularly challenging samples was reconstructed by electron tomography. Due to sample limitations resulting in a large missing wedge and large tilt increments respectively the 3D structure could not be reconstructed by standard iterative algorithms; even a recently developed discrete algorithm failed until the input parameters for discrete reconstruction were improved. These challenges were addressed by adding a mask in each step of the preceding standard iterative reconstruction, setting all voxels known to be vacuum as zero, thus improving the segmentation and the 3D starting model. The position of these vacuum voxels is obtained from TEM images or other measurement data.