EM-tomography of section collapse, a non-linear phenomenon

Area of Science:

• Electron microscopy
• Structural biology
• Materials science

Background:

• Electron tomography (ET) is crucial for high-resolution 3D imaging of biological and material samples.
• Accurate reconstruction in ET depends on sample preparation and imaging conditions, particularly for plastic-embedded sections.
• Understanding section behavior under electron beams is vital for reliable structural analysis.

Purpose of the Study:

• To investigate the impact of electron beam exposure on the thickness and density of Epon and Lowicryl embedded sections.
• To assess the dimensional accuracy of reconstructed structures in plastic sections during ET.
• To determine optimal conditions for minimizing artifacts in ET of embedded materials.

Main Methods:

• Acquisition of tilt series from Epon and Lowicryl embedded sections.
• Reconstruction of 3D volumes using back projection algorithms.
• Analysis of section thickness and density distribution along the electron-optical axis.
• Parallax measurements at 150K to evaluate section collapse.

Main Results:

• Significant thickness reduction observed: 50% for Epon and 80% for Lowicryl sections.
• Non-uniform density distribution along the electron-optical axis, with higher density at vacuum-exposed surfaces.
• Electron exposure levels did not significantly alter reconstructed thickness or density distribution.
• Epon sections showed no collapse at 150K, confirmed by parallax measurements.

Conclusions:

• Plastic embedded sections undergo thickness reduction and density variations during ET.
• Reconstructed structure dimensions are distorted at the top and bottom of sections but accurate in the middle portion.
• Findings are critical for interpreting ET data from plastic embedded samples, especially in materials science and structural biology.