CART: a controlled algebraic reconstruction technique for electron microscope tomography of embedded, sectioned specimen

Reconstruction of thick, embedded, sectioned material has to cope with the restricted tilt view of the electron microscope, with information not stemm ing from the object of interest in the projections, with aberrations of the objective lens and with a distorted relationship between the projected den sities in the micrographs and the specimen mass densities due to incoherent electron interactions within the specimen. Micrograph densities over a ful l tilt-range show in general an averaged mass increase which is more than s hould be expected from the cosine dependency of the tilt-angles of the proj ections. The hereby presented reconstruction technique finds a solution for the under-determined system by a controlled algebraic iteration procedure. For this solution the procedure stabilises the region of interest by dynam ically scaling the input data during the procedure. A model for the electro n transport through thick specimens is proposed and microscope projection s imulations are carried out to test the algorithms. (C) 1999 Elsevier Scienc e B.V. All rights reserved.