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MAXIMUM-ENTROPY AN ELECTRON-TOMOGRAPHY PROGRAM KIT FOR SILICON GRAPHIC COMPUTERS

3D-RECONSTRUCTIONS WITH MAXIMUM-ENTROPY-METHOD

 

We have developed a set of new programs for electron tomography (ET), that works on Silicon Graphics machines. The procedures have been extensively automated. 3D-reconstruction with weighted back-projection (WBP) method of big volumes like human chromosomes at high resolution (Engelhardt and Ruokolainen, 1996), including alignment of electron microscopy tilt-series (41 pictures, 0 to + 60 degrees with a 3 degree increment), takes altogether hours or only minutes to complete in comparison to days with the earlier ET-program kit (Engelhardt et al., 1994a). Superior quality (i.e. practically noise free) 3D-reconstructions are achieved with our maximum-entropy-method (MEM). However, the MEM-program is very calculation intensive and usually takes over night to run also on high performance Silicon Graphics machines (Power Challenge). A very fast and easy method to pick the fiducial gold markers needed for aligning the digitized electron microscopy pictures of a tilt-series, has been achieved by introducing the tilt-series as a stack. Thus the pictures of a tilt-series can be arranged as an interactive film, i.e. pictures can consecutively be exposed, enlarged, moved and image processed, (e.g. contrast enhanced, unsharp filtered - temporarily or permanently) - to aid in the procedure. After running the alignment program, the aligned pictures are visualized as a film in stereo to evaluate the success of the alignment. If necessary, the aligned pictures can progressively be further aligned. The progressive-alignment-procedure has accomplished various initiative alignment difficulties. The selected aligned area is then automatically reconstructed with WBP and MEM programs. As earlier reported Engelhardt et al., 1994a, 1994b, reconstructed volumes are visualized in stereo and in colour with 3D-rendering programs FUNCS (J.R, CSC1) or BOB (freely available from University of Minnesota). With FUNCS we have the advantage to produce compressed (jpeg-formatted) but high quality stereo-films, in colour or in red-green (or blue), around selected axis (0-360 degree with e.g. increments of 10 degree) with different interpolation and light settings. Interpolated stereo-films are excellent substitutes for big volumes. Different regions can be enlarged, moved to suitable position and details can be measured with high precision.

References

Engelhardt P. and Ruokolainen J. (1996) This conference.
Engelhardt P. et al. (1994a) 3D Imaging Sciences in Microscopy, Munich
Engelhardt P. et al. (1994b) Electron Tomography of Chromosomes and Viruses. CSC News 6(4),14-20

1997 / Peter Engelhardt
peter.engelhardt@helsinki.fi