Monte Carlo simulations of electron scattering in bone

Area of Science:

• Materials Science
• Biomaterials Science
• Microscopy Techniques

Background:

• Backscattered electron (BSE) imaging in scanning electron microscopy (SEM) is used to assess bone mineralization.
• Polymethylmethacrylate (PMMA)-embedded bone samples present challenges due to surface topography.
• Understanding the influence of surface features on BSE signals is crucial for accurate bone analysis.

Purpose of the Study:

• To determine the volume element size and shape for BSE imaging in PMMA-embedded bone.
• To investigate the effect of surface topography on BSE signal intensity.
• To explain the origin of contrast observed in bone lamellae during SEM imaging.

Main Methods:

• Modeling BSE signal collection for typical experimental conditions (20 kV, annular detector, 45-75 degree take-off angles).
• Simulating bone surface topography using a sinusoidal profile (wavelength 5.0 µm, amplitude 0.5 µm).
• Analyzing the impact of topographic relief on BSE signal intensity at different surface locations (troughs and crests).

Main Results:

• The collectable BSE signal intensity peaks for electrons leaving the specimen surface approximately 1 micron from the beam impact point.
• Surface topography significantly alters the BSE signal: troughs show a 14.4% reduction, while crests show a 17.2% increase.
• These topographic effects can constructively interfere to produce strong contrast correlated with bone lamellae.

Conclusions:

• The observed lamellar contrast in bone SEM images can be attributed solely to topographic effects.
• Changes in collagen orientation do not necessarily alter mineral packing density.
• Surface topography plays a critical role in interpreting BSE imaging data of bone.