Respect for Tissue Representation Using Photoelastic Stress Analysis for Endovascular Surgery Simulation - Microsurgery: Advances, Simulations, and Applications - page 128

4.2 Vasculature Modeling for Stress Analysis

Silicone elastomer is a photoelastic material, with excellent
mechanical properties for blood vessel modeling; however,
its photoelastic coeficient is too low for enabling a practical
measurement of stress produced by endovascular tools with blood
vessel models. On the other hand, urethane elastomer has enough
sensitivity to visualize stress produced by human blood pressure
ranges or by micro-coil deployment. Single-layer models of urethane
elastomer with low wall thickness are the best selection for
measuring low-magnitude stress ields; however, single-layer models
of urethane elastomer suffer plastic deformation for pressures in
the range of 60-200 mmHg. This plastic deformation is drastically
reduced by shielding the urethane layer with silicone elastomer
layers. Transmittance of light for silicone elastomer is above 88%
for 10 mm thickness and its photoelastic coeficient is several times
smaller than that of urethane elastomer. Shielding layers of silicone
layer are about 60 μ m thick and colorless; the urethane elastomer
layer is about 250 μ m thick and dyed yellow [6]. Therefore, at the
studied pressure ranges, the contribution of silicone elastomer
layers to retardation and transmittance may be neglected.

4.3 Blue Light Transmiance Equation

The measurement of the optical path length is achieved relying on
light attenuation while passing through the photoelastic material.
Blue light is more sensitive to attenuation than red or green light
when passing through yellow-dyed materials. For that reason, and its
high photoelastic coeficient, we selected NIPPOLAN5120 urethane
elastomer dyed yellow with I-01-001Y of Epoch Co. at 0.1w% as
preferred modeling material. Thus, transmittance of blue light was
used to calculate the optical path length in multilayered models of
silicone and urethane elastomer.
For constructing a mathematical model of the blue light
transmittance in urethane elastomer, a urethane elastomer
membrane with variable thickness was built using a stair-case
shaped casting mold. The depth difference between neighbor levels
of the casting mold was 0.2 mm. A blue ilter was placed over a white
light source; an image of the model was captured. The thickness